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EE2401 POWER SYSTEM OPERATION AND CONTROL
UNIT-I - INTRODUCTION
1. What is meant by load curve?
The curve drawn between the variations of load on the power station with reference
to time is known as load curve. There are three types namely d aily load curve,
m onthly load curve and yearly load curve.
2. What is meant by daily load curve?
The curve drawn between the variations of load with reference to various time
period of day is known as daily load curve.
3. What is meant by monthly load curve?
It is obtained from daily load curve. Average value of the power at a month for
different time periods are calculated and plotted in the graph which is known as monthly
load curve.
4. What is meant by yearly load curve?
It is obtained from monthly load curve which is used to find annual load factor.
5. What is meant by connected load?
It is the sum of continuous ratings of all the equipments connected to supply
systems.
6. What is meant by maximum demand?
It is the greatest demand of load on the power station during a given period.
7. What is meant by demand factor?
It is the ratio of maximum demand to connected load.
Demand factor = (max demand)/ (connected load)
8. What is meant by average demand?
The average of loads occurring on the power station in a given period (day or month
or year) is known as average demand.
Daily avg. demand = (no. of units generated per day)/ (24 hours)
Monthly avg. demand = (no. of units generated in month)/ (no. of hours in a month)
Yearly avg. demand = (no. of units generated in a year)/ (no. of hours in a year)
9. What is meant by load factor?
The ratio of average load to the maximum demand during a given period is known
as load factor.
Load factor = (average load) / (maximum demand)
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10. What is meant by diversity factor?
The ratio of the sum of individual maximum demand on power station is known as
diversity factor.
Diversity factor = (sum of individual maximum demand)/(maximum demand).
11. What is meant by capacity factor?
This is the ratio of actual energy produced to the maximum possible energy that
could have been produced during a given period.
Capacity factor= (actual energy produced) / (maximum energy)
12. What is meant by plant use factor?
It is the ratio of units generated to the product of plant capacity and the number of
hours for which the plant was in operation.
Units generated per annum= average load * hours in a year
13. What is meant by load duration curve?
When the load elements of a load curve are arranged in the order of descending
magnitudes, the curve then obtained is called load duration curve.
UNIT-II – REAL POWER FREQUENCY CONTROL
1. What are the major control loops used in large generators?
The major control loops used in large generators are
1. Automatic Voltage Regulator (AVR)
2. Automatic Load Frequency Control (ALFC)
2. What is the use of secondary loop?
A slower secondary loop maintains the fine adjustment of the frequency, and also
by reset action maintains proper MW interchange with other pool members. This loop is
insensitive to rapid load and frequency changes but focuses instead on drift like changes
which take place over periods of minutes.
3. What is the advantage of AVR loop over ALFC loop?
AVR loop is much faster than the ALFC loop and therefore there is a tendency for
the VR dynamics to settle down before they can make themselves felt in the slower load
frequency control channel.
4. What is the difference between large and small signal analysis?
Large signal analysis is used where voltage and power may undergo sudden changes
of magnitude that may approach 100 percent of operating values. Usually this type of
analysis leads to differential equations of non-linear type. Small signal analysis is used when
variable excursions are relatively small, typically at the most a few percent of normal
operating values.
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5. What is meant by exciter?
The exciter is the main component in AVR loop. It delivers the DC power to the
generator field. It must have adequate power capacity and sufficient speed of response (rise
time less than 0.1 sec).
6. What is the function of AVR?
The basic role of the AVR is to provide constancy of the generator terminal voltage
during normal, small and slow changes in the load.
7. What is meant by static AVR loop?
In a static AVR loop, the execution power is obtained directly from the generator
terminals or from the station service bus. The AC power is rectified by thyristor bridges and
fed into the main generator field via slip rings. Static exciters are very fast and contribute to
provide transient stability.
8. Write the static performance of AVR loop?
The AVR loop must regulate the terminal |V| within the required static accuracy
limit. It must have sufficient speed of response and be stable.
9. What is the disadvantage of high loop gain? How is it to be eliminated?
High loop gain is needed for static accuracy but this causes undesirable dynamic
response, possibly instability. By adding series AND/OR feedback stability compensation
to the AVR loop, this conflicting situation can be resolved.
10. What are the effects of generator loading in AVR loop?
Added load does not change the basic features of the AVR loop, it will however
affect the values of both gain factor Kf and the field constant. High loading will make the
generator work at higher magnetic saturation levels. This means smaller changes in |E| for
incremental increases in, if translating into the reduction of KF. The field time constant will
decrease when the generator loading closing the armature current paths. This circumstance
permits the formation of transient stator currents the existence of which yields a lower
effective field induction.
11. What are the functions of ALFC?
The basic role of ALFC is to maintain desired MW output of a generator unit and
assist in controlling the frequency of large interconnection. The ALFC also helps to keep
the net interchange of power between pool members at predetermined values. Control should
be applied in such a fashion that highly differing response characteristics of units of various
types are recognized.
12. Write the disadvantage of ALFC loop?
The ALFC loop will main control only during normal changes in load and
frequency. It is typically unable to provide adequate control during emergency situations,
when large MW imbalances occur.
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13. 13. How is the real power in a power system controlled?
The real power in a power system is being controlled by controlling the driving
torque of the individual turbines of the system.
14. What is the need for large mechanical forces in speed-governing system?
Very large mechanical forces are needed to position the main valve against the high
steam pressure and these forces are obtained via several stages of hydraulic amplifiers
UNIT-III - REACTIVE POWER -VOLTAGE CONTROL
1. What are the sources of reactive power? How is it controlled?
The sources of reactive power are generators, capacitors, and reactors.
These are controlled by field excitation.
2. What are the characteristics of line compensators?
The characteristics of line compensators are,
1. Ferranti effect is minimized.
2. Under excited operation of synchronous generator is not required
3. What is known as bank of capacitors?
When a number of capacitors are connected in parallel to get the desired
capacitance, it is known as bank of capacitors. These can be adjusted in steps by switching
(mechanical).
4. What is the disadvantage of switched capacitors employed for compensation?
When switched capacitors are employed for compensation, these should be
disconnected immediately under light load conditions to avoid excessive voltage rise and
Ferro resonance in presence of transformers.
5. What are the effects of capacitor in series compensation circuit?
The effects of capacitor in series compensation circuit are,
1. Voltage drop in the line reduces
2. Prevents voltage collapse
3. Steady state power transfer increases
4. Transient stability limit increases
6. What is meant by synchronous condenser?
It is a synchronous motor running at no-load and having excitation adjustable over a
wide range. It feeds positive VARs into the line under overexcited conditions and negative
VARs when under excited.
7. Write about Static VAR Compensator (SVC).
These comprise capacitor bank fixed or switched or fixed capacitor bank and
switched reactor bank in parallel. These compensators draw reactive power from the line
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thereby regulating voltage, improve stability (steady state and dynamic), control
overvoltage and reduce voltage and current unbalances. In HVDC application these
compensators provide the required reactive power and damp out sub harmonic oscillations.
8. What is meant by Static VAR Switches or Systems?
Static VAR compensators use switching for VAR control. These are also called
static VAR switches or systems. It means that terminology wise SVC=SVS. And we
will use these interchangeably.
9. List out some of the Static compensators schemes.
1. Saturated reactor
2. Thyristor- Controlled Reactor (TCR)
3. Thyristor Switched capacitor (TSC)
4. Combined TCR and TSC compensator.
10. What is meant by tap changing transformers?
All power transformers and many distribution transformers have taps in one or more
windings for changing the turns ratio. It is called tap changing transformers.
11. Write the types of tape changing transformers.
1. Off- load tap changing transformers.
2. Tap changing under load transformers.
UNIT-IV – COMMITMENT AND ECONOMIC DISPATCH
1. What is the objective of economic dispatch problem?
The objective of economic dispatch problem is to minimize the operating cost of
active power generation.
2. What is meant by incremental cost?
The rate of change of fuel cost with active power generation is called incremental
cost.
3. What is meant by base point?
The present operating point of the system is called base point.
4. What is meant by participation factor?
The change in generation required to meet power demand is called participation
factor.
5. What is meant by hydrothermal scheduling problem?
The objective is to minimize the thermal generation cost with the constraints of
water availability.
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6. What is meant by unit commitment?
Commitment of minimum generator to meet the required demand
7. What is meant by spinning reserve?
It is the term that describes the total amount of generation availability from all units
synchronized on the system.
8. What is meant by scheduled reserve?
These include quick start diesel turbine units as well as most hydro units and
pumped storage hydro units that can be brought online, synchronized and brought up to full
capacity quickly.
9. What is the thermal unit constraint?
Minimum up time, minimum down time and crew constraints. Once the unit is
running, it should not be turned off immediately.
10. What is meant by minimum down time?
Once the unit is recommitted, there is a minimum time before it can be
recommended.
11. What is meant by crew constraints?
If a plant consists of two (or) more units, all the units cannot be turned on at the same
time since there are not enough crew members to attend both units while starting up.
12. What are the two approaches to treat a thermal unit to operating temperature?
The first is to allow the unit boiler to cool down and then heat backup to operating
temperature in time for a scheduled turn on. The second requires that sufficient energy be
given as input to the boiler to just maintain operating temperature.
13. What are the techniques for the solution of the unit commitment problem?
The techniques for the solution of the unit commitment problem are
1. Priority list method
2. Dynamic programming
3. Lagrange relation
14. What are the assumptions made in dynamic programming problem?
A state consists of an array of units with specified units operating. The startup cost of
a unit is independent of the time it has been offline. There are no costs for shutting down the
units.
15. What is meant by long range hydro scheduling problem?
The problem involves the long range of water availability and scheduling of
reservoir water releases, for an interval of time that depends on the reservoir capacities.
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16. What is the optimization technique for long range hydro scheduling problem?
The optimization technique for long range hydro scheduling problem is the Dynamic
programming with hydraulic simulation methods of statistical production cost.
17. What is meant by short range hydro scheduling problem?
It involves the hour by hour scheduling of all generators on a system to achieve
minimum production condition for the given time period.
18. What is meant by system blackout problem?
If any event occurs on a system that leaves it operating with limits violated, the
event may be followed by a series of further actions that switch other equipment out of
service. If the process of cascading failures continues, the entire system of it may
completely collapse. This is referred as system blackout.
19. What is meant by cascading outages?
If one of the remaining lines is now too heavily loaded, it may open due to relay
action, thereby causing even more load on the remaining lines. This type of process is often
termed as cascading outage.
UNIT-V – COMPUTER CONTROL OF POWER SYSTEMS
1. What are the functions of control center?
The functions of control center are as follows:
1. System monitoring
2. Contingency analysis
3. Security constrained optimal power flow
2. What is the function of system monitoring?
System monitoring provides up to date information about the power system.
3. What is meant by SCADA system?
It stands for supervisory control and data acquisition system, allow a few operators to
monitor the generation and high voltage transmission systems and to take action to
correct overloads.
4. What are the states of power system?
The states of power system are normal state, alert mode, contingency mode and
emergency mode.
5. What is meant by alert mode?
In the occurrence of all possible outages when the system does not remain secure it is
called alert mode.
6. What are the distribution factors?
The distribution factors are line outage distribution factor and generation outage
distribution factor.
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7. What is meant by state estimation?
State estimation is the process of assigning a value to an unknown system state
variable based on measurements from that system according to some criteria.
8. What is meant by maximum likelihood criterion?
The objective is to maximize the probability that the estimation of the state variable
x, is the true value of the state variable vector (i.e, to maximize the P(x) = x).
9. What is meant by weighted least-squares criterion?
The objective is to minimize the sum of the squares of the weighted deviations of
the estimated measurements z, from the actual measurement.
10. What is the objective of minimum variance criterion?
The objective is to minimize the expected value of the squares of the deviations of
the estimated components of the state variable vector from the corresponding components
of the true state variable vector.
11. What is meant by must run constraint?
Some units are given a must run status during certain times of the year for reason of
voltage support on the transmission network.
12. What is meant by fuel constraints?
A system in which some units have limited fuel or else have constraints that require
them to burn a specified amount of fuel in a given time.
13. What are the assumptions made in priority list method?
No load cost or zero unit input-output characteristics are linear between zero output
and full load. There are no other restrictions. Startup cost is fixed amount.
14. Write the advantages of forward DP approach.
If the startup cost of a unit is a function of the time it has been offline, then a forward
dynamic program approach is more suitable since the previous history of the unit can be
computed at each stage.
15. Write the disadvantages of dynamic programming method.
It has the necessity of forcing the dynamic programming solution to search over a
small number of commitment states to reduce the number of combinations that must be
tested in each period.
16. What are the known values in short term hydro scheduling problem?
The load, hydraulic inflows & unit availabilities are assumed to be known.
17. What are the functions of security constraints optimal power flow?
In this function, contingency analysis is combined with an optimal power flow
which seeks to make changes to the optimal dispatch of generation, as well as other
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adjustments, so that when a security analysis is run, then no contingency will result in
violations.
18. What is meant by the state of optimal dispatch?
This is the state that the power system is in prior to any contingency. It is optimal
with respect to economic operation but may not be secure.
19. What is meant by post contingency?
Post contingency is the state of the power system after a contingency has
occurred.
20. What are the priorities for operation of modern power system?
Operate the system in such a way that power is delivered reliably. Within the
constraints placed on the system operation by reliability considerations, the system will be
operated most economically.
21. What is meant by linear sensitivity factor?
Many outages become very difficult to solve if it is desired to present the results
quickly. Easiest way to provide quick calculation of possible overloads is linear sensitivity
factors.
22. What are linear sensitivity factors?
Linear sensitivity factors are generation shift factors and line outage distribution
factors.
23. What is the use of line distribution factor?
It is used to apply to the testing for overloads when transmission circuits are lost.
24. What is meant by external equvalencing?
In order to simplify the calculations and memory storage the system is sub divided
into 3 sub-systems called external equvalencing.
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EE2402 PROTECTION AND SWITCHGEAR
UNIT-I
INTRODUCTION
Importance of protective schemes for electrical apparatus and power system
1. What is meant by switchgear? (M/J-06)
Switchgear is a general term covering switching devices and their combinations with
associated control, measuring and protective equipments.
2. What are the consequences of a short circuit?
The consequences of a short circuit are
1. A reduction in the line voltage over a major part of the power system.
2. Damage to the equipments due to overheating.
3. A single line to ground fault in an ungrounded system gives rise to arching
grounds and also the voltages of the other lines are increased by 3 times the
original value which may stress the insulation of the equipments.
4. The stability of the power system is affected.
3. Define – Protective Zone
Protective zone is defined as a part of the system protected by a certain protective scheme.
The entire power system is covered by several protective zones and no part of the system is
left unprotected. Neighbouring zones are overlapped so that no dead spots are left in the
protected system. The boundary of the protective zone is determined by the location of current
transformers which detects and isolates the system by the circuit breakers during abnormal
operation.
4. What are unit system and non-unit system?
A unit protective system is one in which the protection scheme responds to faults in the
protected zone alone whereas non-unit system does not have exact zone boundaries. Each zone
has certain protective scheme and each protective scheme has several protective systems.
5. What is primary protection?
Primary protection is the main protection provided for protecting the equipments. The
primary protection is the first to act and if the primary protection fails, then the backup
protection comes into action and removes the faulty part from the healthy system.
6. What is backup protection?
Secondary protection is the second line of defence which operates if the primary
protection fails to activate within a definite time period. The methods of backup are classified
as relay backup, breaker backup and remote backup.
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7. Distinguish between primary protection scheme and secondary protection scheme.
Main or primary protection can fail due to non-functioning of one of its components in the
protective scheme such as relay, CT, PT, trip circuit or circuit breaker. If the primary protection
fails, then there must be an additional protection, otherwise the fault may remain uncleared
which may result into a disaster. The backup protection is provided either by time grading
principle or by duplication principle to protect the power system.
Relay terminology - Definitions
8. Define – Energizing Quantity
Energizing quantity is defined as the current, voltage or frequency which is used to operate
the relay under abnormal condition.
9. Define – Operating Time of a relay
Operating Time of a relay is defined as the time interval between the occurrence of
fault and closure of relay contact .
10. Define – Resetting Time of a relay
Resetting Time of a relay is defined as the time which elapses between the instant
when the actuating quantity becomes less than the reset value to the instant when
the relay contact returns to its normal position.
11. What is meant by time setting multiplier in protective relaying?
The operating time of the relay depends upon the distance between the moving contact and
the fixed contact of the relay. The distance between the contacts is adjusted by the movement
of the disc back stop which is controlled by rotating a knurled moulded wheel at the base of the
graduated time multiplier scale. This is known as time multiplier setting.
Essential qualities of protection.
12. What are the various essential qualities of protective relaying?
The various essential qualities of protective relaying are
1. Speed
2. Stability
3. Selectivity
4. Sensitivity
5. Simplicity
6. Reliability
7. Economy
13. What are the functions of protective relaying? (A/M-07)
A fault in the equipment in the supply system leads to disconnection of supply to a large portion
of the system. If the faulty part is quickly disconnected, the damage caused by the fault is minimum
and the faulty part can be repaired quickly and the service can be restored without further delay.
Better service continuity has its own merits. Thus the protective relaying helps in improving service
continuity.
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Protection against over voltages due to lightning and switching
14. What are the causes of over voltage?
The causes of over voltage are
1. Lightning
2. Switching
3. Power frequency
15. What are the protective measures that taken against lightning over voltage?
The protective measures taken that against lightning over voltage are,
1. Use of overhead ground wires
2. Low tower footing resistance
3. Use of lightning arresters
16. State the difference between the nominal system voltage and highest system voltage.
The sinusoidal rms voltage is represented for single phase voltage supply as
V = Vmax sin
where V = Nominal system voltage
Vmax = Highest system voltage
Ground wires
17. What is shielding angle of an overhead ground wire? What are the values as per
American and European practices?
The shielding angle of the ground wire is defined as the angle between the vertical line
passing through the ground wire and the line passing through the outermost power conductor.
The shielding angle should be 30º on plain areas whereas the angle decreases on hilly areas
according to the slope of the hill.
American standard - 30º
European standard - 45º
Surge absorber and diverters
18. What is surge absorber? How do they differ from surge diverter? (N/D-11)
The surge absorber acts like an air cored transformer which has a primary low value
inductor and the dissipater acts as a single turn short circuit secondary. Whenever the
travelling wave is incident on the surge absorber, a part of the energy contained in the wave is
dissipated as heat due to transformer action and eddy current flows. Because of this series
inductance, the steepness of the wave gets reduced. It is claimed that the stress in the end
turns is reduced by 15% with the help of the surge absorber.
Lightning arrester or surge diverter limits the duration and amplitude of the flow current
while a surge absorber reduces the steepness of the wave front for a particular surge
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19. What is the significance of the coefficient of earthing in the selection of voltage rating of a
surge arrester?
The coefficient of earthing is given as
The rated voltage of the surge arrester should be more than the phase to ground voltage on
unfaulted phase during a single line to ground fault on any other phase. During a single phase
to earth fault on one phase, the phase to ground voltage of other two healthy phases rises to
(Vm * Ce). The rated voltage of the surge arrester should be more than (Vm * Ce) kV rms
continuous across the terminals.
Va > Vm * Ce kV
where Va = Rated voltage of the surge arrester
Vm = Highest phase to phase voltage
Ce = Coefficient of earthing
Power system earthing
20. Define – Earthing
Earthing is defined as the non current carrying parts of equipment connected to earth.
21. Define – Coefficient of Earthing
Coefficient of Earthing is defined as the ratio of healthy phase to ground voltage to the phase
to phase voltage measured during a single phase to ground fault.
Neutral Earthing
22. What is the difference between equipment earthing and neutral earthing?
Equipment earthing refers to the grounding of non-current carrying metal parts to earth. It is
used for safety of personnel.
Neutral earthing refers to the grounding of current carrying conductor to the earth. It is used
for the safety of equipment and to eliminate arching grounds.
23. List out the advantages of neutral grounding of an electrical system.
The advantages of neutral grounding of an electrical power system are
1. Arching grounds are reduced or eliminated. The system is not subjected to overvoltage
surge due to arching grounds.
2. The voltage of healthy phase lines with respect to earth remains at normal value. They
do not increase to 3 time normal value as in the case of ungrounded system.
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3. The life of insulation is long due to prevention of voltage surges caused by arching
grounds. Thereby it has reduced maintenance, repairs, and breakdowns. It improves
continuity.
4. Stable neutral point.
5. The earth fault relaying is relatively simple. Sufficient quantity of earth fault current is
available to operate the earth fault relay.
6. The over voltages due to lightning are discharged to earth.
7. By employing resistance or reactance in earth connection, the earth fault current can be
controlled.
8. Improved service reliability due to limitation of arching grounds and prevention of
unnecessary tripping of the circuit breaker.
9. Greater safety to personnel and equipment due to operation of fuses or relays on earth
fault and limitation of voltages.
10. Life of equipments, machines, installation is improved due to limitation of voltage.
Hence overall economy increases.
Basic ideas of insulation coordination.
24. Define – Insulation Coordination (N/D-11)
Insulation Coordination is defined as the coordination between the withstand levels of
equipment, protective levels of protective devices with adequate protective margin so that the
overall economy is obtained and least damage is caused to the electrical installation during
overvoltage surges. The insulation level of an apparatus is defined as the combination of
voltage value (both power frequency and impulse) which characterised its insulation with
regard to its capability of withstanding the dielectric stresses.
25. Define – Rated Voltage of Surge Arrester
Rated voltage of surge arrester is defined as the maximum permissible rms voltage between
the line terminal and the earth terminal of the arrester.
UNIT-II
OPERATING PRINCIPLES AND RELAY CHARACTERISTICS
Electromagnetic relays
1. State any two applications of electromagnetic relay. (M/J-08)
The applications of electromagnetic relay are
1. Over/ Under current relays
2. Over/ Under voltage relays
3. Earth fault protection relays
4. Differential protection
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2. What are the fundamental requirements of a relay?
The fundamental requirements of a relay are
1. Speed
2. Stability
3. Selectivity
4. Sensitivity
5. Simplicity
6. Reliability
3. What is the need for relay coordination?
The operation of a relay should be fast and selective. It should isolate the fault in the
shortest possible time causing minimum disturbance to the system. Also, if a relay fails to
operate, there should be sufficiently quick backup protection so that the rest of the system is
protected. By relay coordination, faults can always be isolated quickly without serious
disturbance to the power system.
4. Explain the following:
1. Sensitivity of a relay
Sensitivity of a relay refers to the smallest value of actuating quantity at which the
relay starts operating in relation with the minimum value of fault current in the protected
zone.
2. Stability of a protective system
Stability is defined as the quality of protective system by the virtue of which, the
protective system remains inoperative and stable under certain specified conditions such as
system disturbance through faults and transients.
5. List out the applications of electromagnetic relay.
The applications of electromagnetic relay are
1. Protection of various components
2. It can be used for differential protection
3. Used as auxiliary relays in protective relaying schemes
Over current, directional and non-directional, distance, negative sequence, differential and
under frequency relays
6. What is the purpose of distance relay? (A/M-07)
Distance relays are double actuating quantity relays with one coil energized by voltage
and the other energized by current. The torque is produced in such a way that when V/I
reduce below a set value, the relay operates. Distance relays are widely used protective
devices for the protection of high and extra high voltage transmission line. They can be used
for primary as well as backup protection. Distance relays can be used in carrier aided distance
schemes and also in auto-reclosing schemes.
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7. A relay is connected to 400/5 ratio current transformer with a current setting of 150%.
Calculate the plug setting multiplier when the circuit carries a fault current of 4000 A.
(N/D-11)
Given:
Current transformer turns ratio = 400/5
Current setting = 150%
Primary fault current = 4000 A
To find:
Plug setting multiplier (PSM)
Formula:
Solution:
PSM = 4000/(1.5*(400/5)) = 33.33.
8. Define – Pickup (M/J-06)
Pickup is defined as the operation of a relay. The pickup value is the minimum value of
operating quantity at which the relay operates and closes its contacts.
9. Define – Plug Setting Multiplier (M/J-06)
The plug setting multiplier is given as
10. Define – Over Current Relay
Over current relay is defined as the relay that operates when the current in a line exceeds
its predetermined value. e.g. Induction type non-directional/directional over-current relay,
differential over-current relay.
11. Define – Undercurrent Relay
Undercurrent relay is defined as the relay which operates whenever the current in a circuit
or transmission line drops below its predetermined value. e.g. differential over-voltage relay.
12. What are the different types of over current relays?
The different types of over current relays are
1. Instantaneous Over-current Relay
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2. Time Over-current Relay
3. Inverse Time Over-current Relay
4. Directional Over-current Relay
13. What is directional relay?
The relay which responds to a fault current in a particular direction is called the
directional relay.
Three conditions must be satisfied for its operation. They are current magnitude, time
delay and directionality. The directionality of the current flow can be identified using the
voltage as a reference vector.
14. What are the features of a directional relay?
The features of a directional relay are
1. High speed operation
2. High sensitivity
3. Ability to operate at low voltages
4. Adequate short-time thermal ratio
5. Burden must not be excessive.
15. What is the use of distance relay?
Distance relays respond to the voltage and current, i.e., the impedance, at the relay
location. These are widely used protective devices for the protection of high and extra high
voltage transmission line. It can be used for primary as well as for backup protection.
Distance relays can be used in carrier aided distance schemes and also in auto-reclosing
schemes.
16. Explain the significance of the following terms in the distance protection:
Reach of a distance relay
The limiting distance covered by the relay. The faults beyond this distance are not
covered within the reach of the protection and it will be covered by other protective relay.
Under reach of a distance relay
Under reach of a distance relay is the failure of distance relay to operate within the set
protected transmission line distance.
17. Distinguish between circulating current differential protection and balanced voltage
differential protection with reference to the behaviour of CT.
In circulating current differential protection the principle of circulating current is used
where the balanced voltage differential protection works on the principle of balanced
opposing voltages.
18. List out any two applications of differential relay.
The applications of differential relay are
1. Protection of generator & transformer unit
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2. Protection of large motors
3. Bus bars.
19. What is biased differential bus zone protection?
In biased differential protection, the relay element has a restraining coil in addition to
the operating coil. The circulating current flows through the restraining coil and the spill
current flows through the operating coil. For external faults, the restraining current is more
and the relay does not operate.
20. What is an under frequency relay?
An under frequency relay is one which operates when the frequency of the system
(usually an alternator or transformer) falls below 5 to 10% of its original value.
Introduction to static relays.
21. What are the advantages of static relay? (M/J-06)
The advantages of static relay are
1. No moving contacts (no erosion on contacts)
2. Consumes less power
3. Burdens on CTs and PTs are low
22. State any two advantages of static relay over electromagnetic relay.
The advantages of static relay over electromagnetic relay are
1. In static relays, there are no moving contacts and hence associated problems of
arising, erosion of contacts, replacement of contacts, as in the case of
electromagnetic relays, do not exist.
2. Static relays consume lesser power than the electromagnetic relays. i.e., static
relays have fewer burdens on CT’s and PT’s compared to electromagnetic relays.
Static relays power consumption is one mill watt whereas in electromagnetic
relay, the power consumption is 2 watts.
23. Draw the block diagram of a static relay indicating its basic elements.
Block diagram of a Static relay
19
24. Distinguish between static relay and electromagnetic relay.
For simple protective functions and for protection of simple low power equipment,
electromechanical relays are preferred.
For complex protective functions requiring accurate characteristics for various protective
functions and for protection of costly and large equipments, static relays are preferred. These
may be hard wired or programmable.
25. What is meant by static relay?
A static relay is an electric relay in which the response is developed by
electronic/magnetic/optical or other components, without mechanical motion of its
components. This relay is designed to give an output signal when a threshold condition is
achieved to operate a tripping device.
26. What are the merits and the demerits of a static relay over electromagnetic relay?
Merits and demerits of a static relay over electromagnetic relay are
1. Low power consumption as low as 1mW
2. No moving contacts; hence associated problems of arcing, contact bounce,
erosion, replacement of contacts are avoided.
3. No gravity effect on operation of static relays. Hence it can be used in ships,
aircrafts etc.
4. A single relay can perform several functions like over current, under voltage,
single phasing protection by incorporating respective functional blocks. This is
not possible in electromagnetic relays.
5. Static relay is compact.
6. Superior operating characteristics and its accuracy is more.
7. Programmable operation is possible with static relay.
8. Effect of vibration is negligible; hence it can be used in earthquake-prone areas.
9. Simplified testing and servicing. It can convert even non-electrical quantities to
electrical in conjunction with transducers.
27. List out the applications of static relay.
The applications of static relay are
1. Bus bar protection
2. Transformer protection
3. Transmission line protection
4. Sequential operation tap changing and voltage control
5. Load shedding system restoration etc.,
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UNIT – III
APPARATUS PROTECTION
PART – A
Main considerations in apparatus protection
1. What is meant by time-graded system of protection? (N/D-11)
Time-graded system of protection is a non-unit type of protection which is used when
a time-lag can be permitted and instantaneous operation is not necessary. This is also called a
backup protection to the primary main protection.
2. What are the main safety devices used for a transformer protection?
The main safety devices used for a transformer protection are
1. Buchholz relay
2. Pressure relief value
3. HRC fuses
4. Horn gaps
5. R-C surge suppressors
6. Surge arresters
7. Percentage differential protection
8. Over fluxing and over voltage protection
9. Over current protection
10. Earth fault protection
11. Thermal overload relay
Transformer, generator and motor protection
3. What are the various types of transformer faults? (M/J-08)
The various types of transformer faults are
1. Incipient fault
2. Internal fault
3. Phase-to-phase and phase-to-ground fault
4. Saturation of magnetic circuit
5. Earth fault
6. Through fault
7. Overloading
8. High voltage surges due to lightning
4. Why is the protection of a generator complex? (MJ-08)
The protection of a generator is complex because of the following reasons
1. Generator is connected to the transmission grid through bus bars, transformers and
circuit breakers. The protection requires to ascertain the overload, over/under
voltage, over/under frequency at each instance during its operation. In addition,
21
the stator/rotor faults along with the operating range within the specified
temperature rise of the generator need to be accessed as per standard.
2. The excitation system, prime mover status, automatic voltage regulator status and
its cooling system is not single equipment but comprises of several equipments.
Therefore the protection of generator should be co-ordinated with these
equipments.
3. The continuity of power is the basic requirement since the sudden shut down of
the generator would result in power shortage and would affect the stability of the
power system.
5. What are the limitations of Buchholz relay?
The limitations of Buchholz relay are
1. Incipient faults below oil levels are detected.
2. Setting the mercury switch cannot be too accurate as there can be a false operation
due to its sensitivity during vibrations, earthquakes, mechanical shocks to the pipe
etc.
3. The minimum operating time is 0.1 second and average time is 0.2 second. Such a
slow relay is unsatisfactory for detecting faults in the transformer quickly.
4. These are not provided for transformers below 500 kVA, since it is costly.
5. This protection needs conservator, otherwise the relay cannot be installed.
6. What are the problems that arise in differential protection of a power transformer and
how are they overcome?
The problems that arise in differential protection of a power transformer are
1. Difference in lengths of pilot wires on either side of relays. This difficulty is
overcome by connecting adjustable resistors in the pilot wires.
2. Difference in CT ratios due to ratio and phase angle errors causes the relay
operation during through faults. This difficulty can be overcome by using biased
differential relay or percentage differential relay.
3. Tap changing alters the ratio of voltage between H.V. side and L.V. side in a
transformer. Differential protection should be provided with bias which prevents
the effect of variation in secondary current due to tap changing.
4. Magnetizing inrush current takes place during switching on the transformer. To
avoid this effect, the relay will be provided with a time lag of 0.2 second.
7. What is an over fluxing protection in a transformer?
Power transformers are designed to withstand the ratio of its applied voltage with
respect to frequency (V/f) continuously, where V is the normal highest rms voltage applied
and fn is its frequency. High V/f can occur in a transformer if full excitation is applied to
generator before reaching its full synchronous speed. Over fluxing protection in a transformer
blocks increasing excitation current of a generator before it reaches its full speed.
22
8. State the short comings of Merz-Price protection scheme applied to a power
transformer.
The short comings of Merz-price protection scheme applied to a power transformer are
1. Magnetizing current inrush in a transformer during switching on.
2. Fixed current transformer ratios on a variable ratio power transformers due to its
tap changers.
3. Unavoidably different characteristics of CTs on the high and low voltages sides of
the transformer during through faults.
9. What are the uses of Buchholz relay?
The uses of Buchholz relay are
1. To protect the transformer from incipient faults below the oil level, which results
in the decomposition of oil
2. To give advance warning and prevent the transformer from short circuit condition
and subsequent damage
10. What are the various faults to which a turbo alternator is likely to be subjected?
The various faults to which a turbo alternator is likely to be subjected are
1. Thermal overloading
2. Unbalanced loading
3. Stator winding faults
4. Field winding faults
5. Over voltages
6. Loss of synchronism
7. Over speeding
8. Vibration
9. Excessive bearing temperature
10. Wrong synchronization
11. What are the causes of over speed in an alternator and how is it prevented?
The causes of over speed in an alternator are
1. Sudden loss of electrical load
2. Tripping of circuit breaker before disconnection of prime mover
3. This can be prevented by over speed protection provided along with governing
mechanism.
12. What are the main types of stator winding faults?
The main types of stator winding faults are
1. Phase-to-phase faults
2. Phase-to-earth faults
3. Stator inter-turn faults
4. Three phase fault.
23
13. What is the purpose of adding a neutral resistor between neutral and earth of an
alternator?
The capacitance ground current may not be large enough to demand reactance
grounding and also the ground fault current for solid grounding becomes excessive in 3.3 kV
and 33 kV transmission lines,. Hence it is needed to connect the neutral point through
resistance to ground to reduce its fault current.
14. Why is the backup protection used for an alternator?
If the primary protection fails in an alternator due to failure in CT, PT, trip circuit,
circuit breaker, etc., the backup protection comes into action and removes the faulty part from
the healthy system. When the main protection is made inoperative for the purpose of
maintenance, testing, etc., backup protection acts as the main protection. As a measure of
economy, backup protection is provided with primary protection against short circuits.
Protection of busbars
15. What is the importance of bus bar protection? (M/J-06)
The busbar protection is important because of the following reasons
1. Fault level at busbar is very high
2. The stability of the system is affected by fault in bus zone.
3. The fault in a busbar causes discontinuation of power to a large portion of the
system.
16. What are the types of protections used for bus-bars? (A/M-07)
The types of protections used for bus-bars are
1. Over current protection
2. Differential protection
3. Earth fault protection
4. Over voltage protection
5. Surge voltage protection
Transmission line protection
17. What are the common methods used for line protection? (M/J-06)
The common methods used for line protection are
1. Over current protection
a) Time graded
b) Current graded
2. Distance protection
3. Earth fault protection
4. Differential protection
5. Carrier current protection
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18. Define – Power Line Protection
Power line protection is the protection of transmission lines under fault conditions
using power line as a medium. The use of channels to compare conditions at the terminals of
a power line provides selective means of high speed clearing of end zone faults. This type of
protection includes carrier current protection.
19. What is meant by auto reclosing?
The process of automatic closing of circuit breaker after its opening during temporary
outage of a transmission line is called auto reclosing.
20. List out any two disadvantages of carrier current protection scheme for transmission
line.
The disadvantages of carrier current protection scheme for transmission line are
1. In order to avoid operation due to spurious signals, the carrier and receiver signals
should be set at a higher power level.
2. Amplifier and oscillator are continuously energized and the stability and response
time of these units are constraints.
Zones of protection
21. What are the causes of bus zone faults?
The causes of bus zone faults are
1. Failure of support insulator resulting in earth faults.
2. Flashover across support insulator during over voltages.
3. Heavily polluted insulator causes flashover.
4. Earthquake
5. Mechanical damage etc.
22. What are the problems in bus zone differential protection?
The problems in bus zone differential protection are
1. Large number of circuits.
2. Saturation of CT core during short circuit which introduces ratio error.
3. Sectionalising of bus makes the circuit complicated.
4. Setting of relays needs to be changed with large changes in loads.
CTs and PTs and their applications in protection schemes
23. What is meant by burden on C.T.? (A-07)
The circuit connected to the secondary winding of CT is termed as burden of the
current transformer. Burden is expressed preferably in terms of impedance of the circuit
connected to the secondary. It is specified in volt-ampere at rated secondary current at
specified power factor.
25
24. Why should not the secondary of a current transformer be open? (N/D-11)
If the secondary of a current transformer is opened, then the voltage across the
secondary rises to a high value since there is no back emf. This may cause danger to working
personnel. Also the flux increases and results in the saturation of the transformer core.
Therefore, the secondary of the current transformer should never be opened.
25. What are the merits of carrier current protection?
The merits of carrier current protection are
1. It protects the transmission line if the length of the transmission line is long and
also when the simultaneous opening of circuit breakers at both ends is desirable.
2. Fast clearing prevents shocks to systems .
3. For simultaneous faults, it provides easy discrimination.
4. Tripping due to synchronizing power surges does not occur and it increases
stability of transmission system.
26. What are the various errors of CT?
The various errors of CT are
1. Current error or ratio error
2. Phase angle error
3. Composite error
27. What is meant by a power swing?
During switching of lines, larger loads or generators, surges of real power and
reactive power flow through the transmission lines causing oscillations in the voltage and
current waves. These oscillations are called power swings.
28. What is a programmable relay?
A relay in which the characteristics and behaviour are programmed is called
programmable relay. It has a microprocessor in its circuit. The programme can take care of on
line computation for relay operation and protection purpose.
29. What is a REF relay?
In the absence of earth fault, the vector sum of the line currents Ias + Ibs + Ics is zero.
During earth fault the vector sum of these currents will flow which is called residual current.
The earth fault relay is connected in such a way that the residual current flows through it. If
earth fault occurs, residual current flows through the earth fault relay. If the residual current
is set above pick up value, the earth fault relay operates. In the absence of earth fault, the
residual current is zero and the residually connected earth fault relay does not operate
30. What is meant by field suppression?
When a fault develops in an alternator winding even though the generator circuit
breaker is tripped, the fault continues to be fed because of emf is induced in the generator
itself. Hence the field circuit breaker must be opened and the stored energy in the field
winding is discharged through a resistor. This method is known as field suppression.
26
UNIT – IV
THEORY OF CIRCUIT INTERRUPTION
Physics of arc phenomena and arc interruption
1. What are the factors on which the arc resistance depends? (M/J-06)
The factors on which the arc resistance depends are
1. Length of the arc
2. Voltage across the arc
2. What are the two theories used to describe the arc extinction phenomena?
(M/J-08)
The two theories used to describe the arc extinction phenomenon are
1. Slepian’s theory
2. Energy balance theory
3. Write the different methods of high resistance arc interruption.(MAY/JUNE-2008)
The different methods of high resistance arc interruption are
1. Lengthening the arc by means of arc runners
2. Splitting of arc
3. Cooling of arc
4. What is an arc?
An electric arc is a self-sustained discharge of electricity between electrodes in
a gas or a vapour.
5. What is an arcing ground?
A temporary fault caused by falling of a line creates an arc between phase conductor
and ground. The arc extinguishes and restrikes in a repeated and regular manner. This
phenomenon is called an arching ground which is commonly experienced with ungrounded
systems due to charging and discharging of capacitance between line and earth.
6. What is an arc suppression coil?
Arc suppression coil is provided with tappings. This permits selection of reaction of
the coil depending upon the length of the transmission line and the capacitance of line to
ground to be neutralized. The arc suppression coil is connected between neutral and ground.
7. List out any two methods used for arc interruption.
The methods used for arc interruption are
1. High resistance interruption
2. Low resistance or zero point interruption
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Restriking voltage, Recovery voltage, Rate of rise of recovery voltage, Resistance
switching, Current chopping, Interruption of capacitive current
8. Define – Rate of Rise of Restriking Voltage (A/M-07)
The restriking voltage is the recovery voltage having significant transients which
appears across the terminals of a pole of a circuit breaker after the breaking of current. This
may last for hundreds of microseconds. It may be oscillatory or non oscillatory or
combination of both depending upon the characteristic of the circuit and the type of breaker.
Rate of rise of restriking voltage is expressed in volts per micro-second.
9.-Distinguish between recovery voltage and restriking voltage. (N/D-11)
Sl. No. Recovery voltage Restriking voltage
1
It is the normal frequency r.m.s. voltage
which appears across the terminals of a
circuit breaker after the final current zero.
The restriking voltage is the
voltage having significant
transients which appears
across the breaker poles of a
circuit breaker after the
breaking of current.
2
The instantaneous voltage of the recovery
voltage at the instant of arc extinction is
called active recovery voltage.
The transient voltage that
appears across the contacts at
the instant of arc extinction is
called restriking voltage.
3 It does not restrike after the arc extinction
It appears and immediately
restrikes after the arc
extinction.
10. Which are the factors affecting the transient recovery voltage. (N/D-11)
The factors affecting the transient recovery voltage are
1. Effects of natural frequency of transient recovery voltage
2. Effect of Power factor on transient recovery voltage
3. Effect of Reactance drop on power frequency recovery voltage
4. Effect of Armature reaction on recovery voltage
5. Effect of circuit condition
11. What is restriking voltage?
Restriking voltage is the transient voltage across the breaker poles immediately after
the arc extinction. It lasts for hundreds of micro-second. It may be oscillatory or non-
oscillatory in nature depending upon the characteristics of the circuit and the type of circuit
breaker.
Restrike is defined as the reappearance of an arc after one-fourth cycle from the arc
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extinction at current zero. In capacitor current breaking, a single restrike gives an overvoltage
of about 4 times and a second restrike gives an overvoltage of about 6 times of the normal
power frequency voltage resulting in internal and external flashovers between phase to phase
as well as phase to ground.
12. Explain, “successive restrikes” and current chopping as applied to the interruption
of capacitive and low inductive currents.
The energy stores in inductance during current interruption are diverted to the
capacitance at the moment of current interruption.
Also capacitor banks are connected in the network to provide reactive power at
leading power factor. The voltage across a capacitor cannot change instantaneously. The
currents supplied to the capacitor are generally of small order and the circuit breaker can
interrupt such currents invariably at the first current zero. Due to the 90º phase difference, the
voltage across the capacitor is at maximum value (ec) at this instant (t1) and the capacitor
remains charged at this voltage (ec). After half cycle (t2) the recovery voltage of approximate
magnitude of (ermax) appears across the circuit breakers and the total voltage across the circuit
breaker is the sum of the two voltages.
eTmax = ermax + ec
where eTmax = maximum voltage across breaker
ermax = maximum value of power frequency recovery voltage
ec = voltage across the capacitor
Thus the recovery voltage of the order of 2Emax, appears across the circuit breaker
pole at the instant t2, after ½ cycle of current zero. Therefore, a restrike is possible.
If a restrike occurs, the LC circuit will oscillate at a frequency given by fn = ½ (LC).
This current tries to maintain the arc. The voltage across the interrupter rises up to 4 times the
normal voltage due to one restrike and up to 6 times with second restrike. The energy to be
dissipated during such arcs is quite large and the interrupters may get damaged in the process
after a restrike.
13. How can restriking transients be damped by connecting a resistance across the
contacts of a circuit breaker?
In resistance switching, a resistance is connected in parallel with the contacts of the
circuit breaker. With the arc so shunted by the resistance a part of an arc current flows
through the resistance. This results in a decrease in arc current and an increase in the rate of
deionization of the arc path and the resistance of the arc. This leads to a further increase in
the current through the shunt resistances. This built up process continues until the current
path through the arc is substituted by that through the resistance either wholly or in greater
part. In the later case, the small value of the current remaining in the arc path becomes so
instable that it gets easily extinguished.
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14. Explain the following terms:
a. Symmetrical breaking capacity
b. Asymmetrical breaking capacity
c. Making capacity
Symmetrical breaking capacity
Symmetrical breaking capacity is the product of symmetric breaking current and
recovery voltage.
Asymmetrical breaking capacity
The Asymmetrical breaking capacity is the product of an asymmetrical breaking
current and the recovery voltage.
Making capacity
Making capacity is the peak value of the maximum current loop including DC
component in a phase during the first cycle of current when the circuit breaker is closed. The
making capacity is specified by the product of making current it can make and carry
instantaneously at the rated service voltage without increasing the temperature rise of its
current carrying parts.
15. An OCB is rated for 1000 MVA, 2 kA, 66 kV, 3 phase, 3 second. Determine the
following:
a. Rated operating voltage
b. Rated operating current
c. Rated symmetrical breaking current
Given data:
Rating of OCB = 1000 MVA
Rated current = 2 kA
Rated voltage = 66 kV
No. of phase = 3
Time period = 3 second
To find:
a) Rated operating voltage
b) Rated operating current
c) Rated symmetrical breaking current
Formula required:
Rated symmetrical breaking current = Rating of the circuit breaker / ( 3 x
Rated voltage)
Solution:
Rated operating voltage = Rated voltage = 66 kV
Rated operating current = Rated current = 2 kA
Rated symmetrical breaking current = (1000 x 106) / ( 3 x 66 x 10
3)
= 8750 A
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UNIT-V CIRCUIT BREAKERS
Types of circuit breaker
1. What is a circuit breaker?
A circuit breaker is an automatic switch which can interrupt fault currents.
2. List out the classification of circuit breakers based on the medium used for arc
extinction.
The classifications of circuit breakers based on the medium used for arc extinction are
1. Air break circuit breaker or Miniature circuit breaker
2. Oil circuit breaker
3. Minimum oil circuit breaker
4. Air blast circuit breaker
5. Sulphur hexafluoride circuit breaker
6. Vacuum circuit breaker
3. List out any two applications of a differential relay.
The applications of a differential relay are
1. Protection of generator
2. Protection of generator-transformer unit
3. Protection of transformer
4. Protection of transmission line
5. Protection of bus zone
4. List out all the three symmetrical components.
The three symmetrical components are
1. Positive sequence component
2. Negative sequence component
3. Zero sequence component
5. Define – Positive Sequence Component
Positive sequence component is defined as a component which has three vectors of
equal magnitude but displaced in phase from each other by 120º and has the same phase
sequence as the original vectors.
6. Define – Zero Sequence Component
Zero sequence component is defined as a component which has three vectors of equal
magnitude and also are in phase with each other.
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7. Define – Negative Sequence Component
Negative sequence component is defined as a component which has three vectors of
equal magnitude but displaced in phase from each other by 120º and has the phase sequence
opposite to the original vectors.
8. What is resistance switching?
Resistance switching is the deliberate connection of a resistance in parallel with the
contact space (arc). It is used in circuit breakers having high post zero resistance of contact
space (air blast circuit breaker).
9. What is meant by current chopping? (M/J-06)
When interrupting low inductive currents such as magnetizing currents of transformer
or shunt reactor, the rapid deionization of contact space due to air blast may cause the current
to be interrupted before its natural zero. This phenomenon of the interruption of current
before its natural zero is called current chopping.
10. Which is the method used for capacitive switching?
The problems faced in transmission line during following events are
1. Switching of capacitor banks
2. Switching of unloaded transmission lines
3. Switching of unloaded cables
4. Opening of long transmission line on no load
5. Disconnection of capacitor banks
This can be avoided by resistance switching whereby a resistance is connected in
parallel with the contacts of the circuit breaker. With the arc so shunted by the resistance a
part of an arc current flows through the resistance. This results in a decrease in arc current
and an increase in the rate of deionization of the arc path and the resistance of the arc. This
leads to a further increase in the current through the shunt resistances. This built up process
continues until the current path through the arc is substituted by that through the resistance
either wholly or in greater part. In the later case, the small value of the current remaining in
the arc path becomes so unstable that it gets easily extinguished.
11. A circuit breaker is rated at 1500 amps, 2000 MVA, 33 kV, 3 sec, 3-phase, oil circuit
breaker. Determine the rated normal current, breaking current, making current and
short time rating (current).
Given data:
Rated current of circuit breaker = 1500 A
Rating of the circuit breaker = 2000 MVA
Rated voltage = 33 kV
No. of phase = 3
Time = 3 second
To find:
Rated normal current
32
Breaking current
Making current
Short time rating
Formula required:
Rated normal current = Rated current of the circuit breaker
Breaking current = Rating of the circuit breaker / ( 3 x Rated voltage)
Making current = 2.55 x Breaking current
Short time rating = Breaking current
Solution:
The rated normal current is 1500 amps.
Breaking current =2000/ ( 3 33) =34.99kA
Making current =2.55 34.99 =89.22kA
Short time rating =34.99 kA for 3 sec.
12. A circuit breaker is rated at 1200 amps, 1500 MVA, 33 kV, 3 sec, 3-phase, oil circuit
breaker. Determine the rated normal current, breaking current, making current and
short time rating (current).
Given data:
Rated current of circuit breaker = 1200 A
Rating of the circuit breaker = 1500 MVA
Rated voltage = 33 kV
No. of phase = 3
Time = 3 second
To find:
Rated normal current
Breaking current
Making current
Short time rating
Formula required:
Rated normal current = Rated current of the circuit breaker
Breaking current = Rating of the circuit breaker / ( 3 x Rated voltage)
Making current = 2.55 x Breaking current
Short time rating = Breaking current
Solution:
The rated normal current is 1200 amps.
Breaking current =1500/ ( 3 33) = 26.25 kA
Making current =2.55 26.25 = 67 kA
Short time rating = 26.25 kA for 3 sec
33
EE2403 SPECIAL ELECTRICAL MACHINES
UNIT-I - SYNCHRONOUS RELUCTANCE MOTOR
1. What is meant by synchronous reluctance motor?
A reluctance motor is a type of synchronous electric motor which induces
non- permanent magnetic poles on the ferromagnetic rotor. Torque is generated through
the phenomenon of magnetic reluctance. The stator consists of multiple salient (ie.
projecting) electromagnet poles, similar to a wound field brushed DC motor. The rotor
consists of soft magnetic material, such as laminated silicon steel, which has multiple
projections acting as salient magnetic poles through magnetic reluctance. The number of
rotor poles is typically less than the number of stator poles, which minimizes torque ripple
and prevents the poles from all aligning simultaneously - a position which cannot
generate torque.
2. Write the characteristics of synchronous reluctance motor.
The synchronous reluctance motor is not self starting without the squirrel cage.
During run up it behaves as an induction motor but as it approaches synchronous speed, the
reluctance torque takes over and the motor locks into synchronous speed.
3. Write the applications of synchronous reluctance motor.
Synchronous reluctance motor is used where regulated speed control is required in
applications such as metering pumps and industrial process equipment.
4. What are the classifications of synchronous reluctance motor?
The classifications of synchronous reluctance motor are as follows: 1. Axially laminated
2. Radially laminated
5. What are the primary design considerations of SYRM?
The primary design considerations of SYRM are
1. High output power capability
2. Ability of the rotor to withstand high speed
3. High reliability
4. Low cost
5. High efficiency
6. Define – Power Factor
PFmax = (Ld/Lq-1) / (Ld/Lq+1)
Higher Ld/Lq ratios yield higher power factors, which corresponds to reduced I2R
losses and reduce volt ampere ratings of the inverter driving the machine.
7. What are the applications of the torque-speed characteristics of SYRM?
The applications of the torque-speed characteristics of SYRM are
1. Comparable power density but better efficiency than induction motor
2. Slightly lower power factor
34
8. What are advantages of SYRM over pm machine?
The advantages of SYRM over pm machine are
1. More reliable than PM machine
2. There need not be any excitation field as torque is zero
3. Eliminated electromagnetic spinning losses.
9. What are applications of SYRM?
The applications of SYRM are
1. Synthetic fiber manufacturing equipment
2. Wrapping and folding machine
3. Auxiliary time mechanism
4. Synchronized conveyors
5. Metering pumps
10. What is meant by vernier motor?
It is an unexcited reluctance type synchronous motor. The peculiar feature of this
motor is that a small displacement of the rotor produces a large displacement of the axis of
maximum and minimum permeance.
11. What are the advantages of SYRM?
The advantages of SYRM are
1. Freedom from pm
2. Ability to maintain full load torque at zero speed
3. A wide speed range at constant power
12. What are the classifications of SYRM?
The classifications of SYRM are
1. Rotor configuration i)cage rotor for line start
2. Cageless-rotors for variable speed
3. Stator windings
4. Stator current controlled mode
13. What are the rotor configurations of SYRM?
The rotor configurations of SYRM are
1. Rotor configuration
2. Cage rotor for line start
3. Cageless-rotors for variable speed
14. What is meant by slow-speed synchronous timing motors?
An aluminum cup supports the magnet. The stator has one coil, coaxial with the shaft.
At each end of the coil is a pair of circular plates with rectangular teeth on their edges, formed
so that they are parallel with the shaft. They are the stator poles. One of the pair of discs
distributes the coil's flux directly, while the other receives flux that has passed through a
common shading coil.
35
15. What is meant by Watthour-meter motors?
These are essentially two-phase induction motors with permanent magnets that retard
rotor speed, so their speed is quite accurately proportional to wattage of the power passing
through the meter. The rotor is an aluminum-alloy disc, and currents induced into it react with
the field from the stator. One phase of the stator is a coil with many turns and a high
inductance, which causes its magnetic field to lag almost 90 degrees with respect to the
applied (line/mains) voltage. The other phase of the stator is a pair of coils with very few turns
of heavy-gauge wire, hence quite-low inductance. These coils are in series with the load.
16. How does the Watthour meter motors look like?
The core structure, seen face-on, is akin to a cartoon mouth with one tooth above and
two below. Surrounding the poles ("teeth") is the common flux return path. The upper pole
(high-inductance winding) is centered, and the lower ones equidistant. Because the lower coils
are wound in opposition, the three poles cooperate to create a "sidewise" traveling flux.
The disc is between the upper and lower poles, but with its shaft definitely in front of the field;
so the tangential flux movement makes it rotate.
17. What are electronically commutated motors?
Such motors have an external rotor with a cup-shaped housing and a radially
magnetized permanent magnet connected in the cup-shaped housing. An interior stator is
positioned in the cup-shaped housing. The interior stator has a laminated core having grooves.
Windings are provided within the grooves. The windings have first end turns proximal to a
bottom of the cup-shaped housing and second end turns positioned distal to the bottom. The
first and second end turns electrically connect the windings to one another. The permanent
magnet has an end and face the bottom of the cup-shaped housing. At least one galvano-
magnetic rotor position sensor is arranged opposite the end face of the permanent magnet so as
to be located within a magnetic leakage of the permanent magnet and within a magnetic
leakage of the interior stator. The at least one rotor position sensor is designed to control
current within at least a portion of the windings. A magnetic leakage flux concentrator is
arranged at the interior stator at the second end turns at a side of the second end turns facing
away from the laminated core and positioned at least within an angular area of the interior
stator in which the at least one rotor position sensor is located
18. What is a repulsion motor?
Repulsion motors are wound-rotor single-phase AC motors that are similar to universal
motors. In a repulsion motor, the armature brushes are shorted together rather than
connected in series with the field. By transformer action, the stator induces currents in the
rotor, which create torque by repulsion instead of attraction as in other motors. Several
types of repulsion motors have been manufactured, but the repulsion-start induction-run (RS-
IR) motor has been used most frequently. The RS-IR motor has a centrifugal switch that
shorts all segments of the commutator so that the motor operates as an induction motor once it
has been accelerated to full speed. Some of these motors also lift the brushes out of contact
with the commutator once the commutator is shorted. RS-IR motors have been used to provide
high starting torque per ampere under conditions of cold operating temperatures and poor
source voltage regulation
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19. What is meant by slip?
If the rotor of a squirrel runs at high speed, the flux in the rotor at any given place
on the rotor would not change, and no current would be created in the squirrel cage. For this
reason, ordinary squirrel-cage motors run at some tens of rpm slower than synchronous speed,
even at no load. Because the rotating field (or equivalent pulsating field) actually or
effectively rotates faster than the rotor, it could be said to slip past the surface of the rotor. The
difference between synchronous speed and actual speed is called slip, and loading the motor
increases the amount of slip as the motor slows down slightly.
20. Write the formula for the speed of the AC motor.
The speed of the AC motor is determined primarily by the frequency of the AC supply
and the number of poles in the stator winding, according to the relation:
Ns = 120F / p
where,
Ns = Synchronous speed, in revolutions per minute
F = AC power frequency
p = Number of poles per phase winding
UNIT – II - STEPPER MOTORS
1. What is meant by stepper motor?
A stepper motor is a digital actuator whose input is in the form of programmed
energization of the stator windings and whose output is in the form of discrete angular
rotation.
2. Define – Step Angle
Step angle is defined as the angle through which the motor rotates for each
command pulse. It is denoted as β.
Β = (Ns-Nr/Ns.Nr) 360 (or) 360/(mNr)
3. Define – Slewing Slewing is defined as the angle at which the stepper motor operates at very high speed.
i.e. (25000 steps per sec).
4. Define – Resolution
Resolution is defined as the no. of steps needed to complete one revolution of the shaft.
Resolution = no. of steps /revolution
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5. List out the applications of stepper motor. The applications of stepper motor are
1. Floppy disc drives
2. Qurtz watch
3. Camera shutter operation
4. Dot matrix and line printers
5. Small tool application
6. Robotics
6. What are the advantages and disadvantages of stepper motor?
Advantages:
1. It can be driven in open loop without feedback
2. It is mechanically simple
3. It requires little or no maintenance.
Disadvantages:
1. Low efficiency
2. Fixed step angle
7. Define – Holding Torque
Holding torque is defined as the maximum load torque which the energized stepper
motor can withstand without slipping from equilibrium position
8. Define – Detent Torque Detent torque is defined as the maximum torque which the unenergised stepper
motor can withstand without slipping. It is also known as cogging torque.
9. What is meant by full step operation?
Full step operation or single phase on mode is the one in which at a time only one
phase winding is energized, due to which one stator winding is energized and causes the rotor
to rotate some angle.
10. What is meant by two phase mode of operation?
Two phase on mode is the one in which two phase windings are energized at a time,
due to which two stator windings are energized and causes the rotor to rotate through some
angle.
11. Define – Pull-in Torque
It is defined as the maximum torque the stepper motor can develop in start – stop mode
at a given stepping rate Fs (step/sec) without losing synchronism.
12. Define – Pull-out Torque
It is the maximum torque the stepper motor can develop in slewing mode at a given
stepping rate Fs (step/sec) without losing synchronism.
13. What is meant by synchronism in stepper motor?
It is the one to one correspondence between the number of pulses applied to the stepper
motor and the number of steps through which the motor has actually moved.
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14. Define – Mid Frequency Resonance in stepper motor
Mid frequency resonance in stepper motor is defined as the phenomenon at which the
motor torque drops to a low value at certain input pulse frequencies.
15. Define – Static Stiffness
It is defined as a measure of ability of the actuator to resist disturbing torques and
forces and thereby to maintain position. It is defined as, S=torque / rad
16. Write the types of driver circuits.
The types of driver circuits are
1. Resistance or L/R drive
2. Dual voltage or bi-level drive
3. Chopper drive
17. What is meant by multi stack VR motor?
Multi stack VR motor is the one in which the stepper motor has three separate
magnetically isolated sections or stacks. Here the rotor and stator teeth are equal.
18. What is meant by micro stepping, in stepper motor?
The methods of modulating currents through stator windings so as to obtain rotation of
stator magnetic field through a small angle to obtain micro stepping action is known as micro
stepping.
19. What are the advantages of micro stepping?
The advantages of micro stepping are as follows: 1. Improvement in resolution.
2. Dc motor like performance
3. Elimination of mid frequency resonance
4. Rapid motion at micro stepping rate.
20. Define – Bandwidth in stepper motor
It is defined as a measure of the frequencies upto which the actuator or servo motor
system can respond.
UNIT-III
SWITCHED RELUCTANCE MOTOR
1. What is switched reluctance motor?
It is a doubly salient, single excited motor. This means that it has salient poles on both
rotor and the stator. But only one member carries the winding. The rotor has no windings,
magnets or case windings.
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2. What are the advantages of SRM? 1. The advantages of SRM are
Construction is very simple
2. Rotor carries no winding
3. No brushes and requires less maintenance
3. What are the disadvantages of SRM?
The disadvantages of SRM are
1. It requires a position sensor
2. Stator phase winding should be capable of carrying magnetizing currents
4. Why i s rotor position sensor essential for the operation of switched reluctance
motor?
It is necessary to use a rotor position sensor for commutation and speed feedback. The
turning on and off operation of the various devices of power semiconductor switching
circuit is influenced by signals obtained from rotor position sensor.
5. What are the different power controllers used for the control of SRM?
The different power controllers used for the control of SRM are
1. Using two power semi conductors and two diodes per phase
2. Phase windings and bifilar wires
3. Dump – C converter
4. Split power supply converter
6. What are the applications of SRM?
The applications of SRM are
1. Washing machines
2. Fans
3. Robotic control applications
4. Vacuum cleaner
5. Future auto mobile applications
7. What are the two types of current control techniques?
The two types of current control techniques are
1. Hysteresis type control
2. PWM type control
8. What is meant by energy ratio?
Energy ratio = Wm / (Wm + R) = 0.45
Wm = mechanical energy transformed
This energy cannot be called efficiency as the stored energy R is not wasted as a
loss but it is feedback to the source through feedback diodes.
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9. Write the characteristics of SRM.
The characteristics of SRM are
1. Lowest construction complexity, many stamped metal elements
2. Like a BLDC or stepper without the magnets
3. High reliability (no brush wear), failsafe for Inverter but...acoustically noisy
4. High efficiency
10. Write the voltage, power range of SRM.
Industrial
Voltage Motor Power Speed Range
100 - 240 Vac 50W - 10'sKW
0 - 60,000 RPM
Automotive
Voltage Motor Power Speed Range
12 - 42Vdc 50W -1kW 0 - 20,000 RPM
11. What is called control system of SRM?
The control system is the responsible for giving the required sequential pulses to the
power circuitry in order to activate the phases as required. There are two options for producing
the sequence including a microcontroller to produce the signal or a timer circuit which could
also produce the desired signal
12. What is meant by timer circuit of SRM?
The use of a timer circuit would be very effective in producing the necessary signal in
which to control the circuit. As the required signal is very simple it could easily be
implemented by digital timer, such as the 555 timer. A digital timer is more precise than
any other form of timer, such as a mechanical timer. With the widespread use of digital
logic within integrated circuits the cost of these timers has reduced considerably. The latest
controllers in use incorporate programmable logic controllers (PLC’s) rather than
electromechanical components in its implementation. Within PLC’s, the timers are normally
simulated by the software incorporated in the controller; the timer is therefore controlled by
the software. There are obvious advantages to this system, although the control of a soft
start could be hard to implement in this way.
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13. Write the soft starters of SRM.
Mechanical – come in the form of torque limiters utilizing clutches and various couplings,
Electrical – these soft starters alter the power supply to the motor to reduce the torque and
current demand. This is normally performed either by reducing the supply voltage, or
controlling the frequency of excitation. Since switched reluctance motors are driven by a
controlled pulsed supply, frequency control is an obvious choice in this case.
14. What are the goals to control soft starting? Fixed start-up time - the start up will be controlled to achieve full speed within a fixed time
Current limit - the motor current can be monitored and the start up controlled to keep it below a specified limit
Torque limit - an intelligent starter can calculate the motor torque based on the current and voltage demand and control the start up to provide a constant starting torque
15. What are the major advantages of frequency control of SRM?
This has a major advantage of being easily controlled and changed at any point by
simply altering the programming. By using this method the development time is reduced
and the number of modules to implement is also reduced.
16. What is meant by isolation of SRM?
The electrical isolation of the control and power circuitry modules is defined as a very
important and is used so that the control electronics are protected from any voltage
fluctuations in the power circuitry. The major method of isolation used today are opto-
isolators, these isolators use short optical transmission paths to transfer a signal from one part
of a circuit to another. The isolator incorporates a transmitter and a receiver, the signal
therefore converts fromelectrical to optical before converting back to electrical thereby
breaking any electrical connection between input and output.
17. What are the current control schemes?
The current control schemes are
1. Hysteresis type current regulator
2. PWM type current regulator
UNIT -IV
PERMANENT MAGNETS AND BRUSHLESS DC MOTORS
1. What are the advantages of brushless dc motors drives?
The advantages of brushless dc motors drives are
1. Regenerative braking is possible
2. Speed can be easily controllable
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2. W hat are the disadvantages of brushless dc motors drives?
The disadvantages of brushless dc motors drives are
1. It requires a rotor position sensor
2. It requires a power semiconductor switching circuits.
3. Define – Mechanical Commutator
Mechanical commutator is defined as an arrangement is located in the rotor. No. of
commutator segments are very high .
4. List out the applications of PMBL DC motor.
The applications of PMBL DC motor are
1. Power alternators
2. Automotive applications
3. Computer and Robotics applications
4. Textile and Glass industries
5. What are the disadvantages of conventional DC motor?
The disadvantages of conventional Dc motor are
1. Field magnets on the stator
2. Maintenance is high
6. Why is the PMBLDC motor called electronically commutated motor?
The PMBL DC motor is also called electronically commutated motor because the
phase windings of PLMBL DC motor is energized by using power semiconductor
switching circuits. Here the power semiconductor switching circuits act as a commutator.
7. What are the classifications of BLPM DC motor?
The classifications of BLPM DC motor are
1. BLPM square wave motor
2. BLPM sine wave motor
8. What are the two types of BLPM SQW DC motor?
The two types of BLPM DC motor are
1. 180 pole arc BLPM SQW motor
2. 120 pole arc BLPM SQW motor
9. What are the two types of rotor position sensors?
The two types of rotor position sensors are
1. Optical position sensor
2. Hall-effect position sensor
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UNIT -V
PERMANENT MAGNETS AND SYNCHRONOUS MOTORS
1. What is meant by stator?
Stator is made up of silicon steel stampings. Stator slots carry a balanced 3phase
armature winding, wound for a specified even number of poles. The ends of the armature
windings are connected to the terminals of the motor.
2. What is meant by rotor?
Rotor is made up of forged steel with outward projected poles. The number of
rotor poles must be same as that of stator. These rotor poles carry field coils. They are
suitably connected to form a field winding. The ends of the field windings are connected
to the two slip rings which are also mounted on to the same shaft.
3. What are the merits of a 3 phase BLPM synchronous motor?
The merits of a 3 phase BLPM synchronous motor are
1. It runs at a constant speed.
2. No sliding contacts so it requires less maintenance.
4. What is the demerit of 3 phase BLMP synchronous motor?
Power factor of operation cannot be controlled as field current cannot be
controlled.
5. What are the rotor configurations? 1. Peripheral
2. Interior
3. Claw-pole or Lundell
6. What are the advantages of load commutation?
The advantages of load commutation are
1. It does not require commutation circuits
2. Frequency of operation can be higher
7. What are the applications of load commutation?
Some prominent applications of this drive are high speed and high power drives
for compressors, blowers, conveyers and steel rolling.
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8. What are advantages of synchronous motor?
The advantages of synchronous motor are
1. Four quadrant operation with regenerative braking is possible
2. High power ratings(up to 100MW)and run at high speeds(6000rpm)
9. What are the applications of synchronous drive?
The applications of synchronous drive are
1. High speed and high power drives
2. Compressors
3. Blowers
4. Fans
5. Pumps
6. Aircraft test facilities
10. What are the features of permanent magnet synchronous motor?
The features of permanent magnet synchronous motor are
1. Robust
2. Compact
3. Less weight
4. High efficiency
11. What are the advantages of load commutation?
The advantages of load commutation are
1. It does not require commutation circuits
2. Frequency of operation can be higher
12. What are the applications of PMSM?
The applications of PMSM are
1. Used as a direct drive traction motor
2. Used as high speed and high power drives for compressors, blowers, conveyors,
etc.
13. What are features of closed-loop speed control of load commutated inverter fed
synchronous motor drive? 1. High efficiency
2. Four quadrant operation with regeneration braking is possible
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MG2351 – PRINCIPLES OF MANAGEMENT
UNIT I - OVERVIEW OF MANAGEMENT
1. What is Management? Management is the process of giving direction and controlling the various
activities of the people to achieve the objectives of an organization.
2. Define – Management According to knootz & Weihrich ―management is the process of designing and
maintaining of an environment in which individuals working together in groups
efficiently accomplished selected aims‖.
3. What is Time study? The movements which takes minimum time is the best one .
4. What is motion study? Taylor suggested that eliminating wasteful movements and performing only
necessary movements.
5. Write Henry fayol’s fourteen principles of management. 1. Division of work. 2. Authority and Responsibility.
3. Discipline
4. Unity of command
5. Unity of direction
6. Individual interest to general interest.
7. Remuneration.
6. What is authority? It is the power given to a person to get work from his subordinates.
7. What is responsibility? It is the amount of work expected of forma man by his superior.
8. What is centralization? The organization is centralized when the power is concentrated with one person.
9. What is scalar chain? The instruction and orders should be sent from the top management to the lower management.
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10. What are management levels? 1. Top-level management. 2. Middle level management
3. Lower level management
11. Write some important functions of top management.
1. To formulate goals and policies of the company
2. To formulate budgets
3. To appoint top executives
12. What is social responsibility? Society is the part of the management to initiate actions either to protect social
interest of the society.
13. What is ethics?
All individuals in business or non-business activities are concerned with some standardized form of behaviour are known as ethics.
UNIT II - PLANNING
1. What is planning? Planning is the process of selecting the objectives and determining the course of
action required achieving these objectives.
2. List out the features of planning. 1. Planning – a primary function 2. Planning - a dynamic process
3. Planning – based on objectives and policies
4. Planning – a selective process
5. Planning – an intellectual process
6. Planning is based on facts
3. Define – Mission Mission is defined as a statement which defines the role that an organization plays in the society.
4. What is meant by strategies? Strategy of an organization is the programme of action and deployment of resources to attain its objectives.
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5. What is procedure? A procedure is a chronological order of actions required to implement a policy and to achieve an objectives.
6. What is objective? Objectives are the aims, purposes or goals that an organization wants to achieve over varying periods of time.
7. What is MBO? MBO is a process whereby, the superior and the subordinate managers of an enterprise jointly identify its common goals, define each individual’s major areas of responsibility in terms of results expected of him, and use these measures as guides for operating the unit and assessing the contribution of its members.
8. What is planning premises? The assumptions about future derived from forecasting and used in planning are known as planning premises.
9. What are the techniques useful while evaluating alternatives? The techniques useful while evaluating alternatives are:
1. Quantitative and Qualitative analysis 2. Marginal analysis 3. Cost effectiveness analysis
UNIT III - ORGANIZING
1. List out the steps involved in organization process. 1. Determination of activities 2. Grouping of activities
3. Assignment of Duties
4. Delegation of authority
2. Write the three categories of span of management. 1. Direct single relationship 2. Direct group relationships
3. Cross relation
3. What are the various types of departmentation?
The various types of departmentation are:
1. Departmentation by numbers 2. Departmentation by time
3. Departmentation by Enterprise function
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4. Departmentation by Territory or Geography
5. Departmentation by customers
6. Departmentation by Equipment or process
7. Departmentation by Product or service
4. List out the sources of authority. 1. Formal authority theory 2. Acceptance authority theory
3. Competence theory
5. What is line authority? Line authority is the direct authority which a superior exercises over a number of subordinates to carry out orders and instructions. In organization process, authority is delegated to the individuals to perform the activities.
6. What is staff authority? The relationship between a staff manager and the line manager with whom he works depends in part on the staff duties.
7. What is job analysis? Job analysis is a detailed study of a job to identify the skills, experience and aptitude required for the job.
8. What is job design? The job design is usually broad enough to accommodate people’s need and desires.
9. What is job rotation?
Job rotation refers in the movement of an employee from the job to another .
10. What is selection? Selection is the process of finding out the most suitable candidate to the job out of the candidates attracted.
11. What is orientation? Orientation refers to the activities involved in introducing the new employees to the organization and its policies, procedures, rules, and regulations.
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UNIT IV - DIRECTING
1. What is job enrichment? Job enrichment is therefore based on the assumption that in order to motivate personnel, the job itself must provide opportunities for achievement, recognition, responsibility, advancement and growth.
2. What is communication? Communication is passing of information from one person to another person.
3. List out the different types of communication flow.
The different types of communication flow are:
1. Downward communication 2. Upward communication
3. Horizontal or lateral communication
4. What are the barriers involved in effective communication? 1. Physical barriers 2. Socio-psychological or personal barriers.
3. Organizational barriers.
4. Semantic barriers.
5. Mechanical barriers.
5. What are the important assumptions made in X theory? 1. The average human dislikes to work. He will avoid work if it is possible. 2. Therefore people must be controlled, directed and threatened with punishment.
6. What is Laissez-faire? Complete freedom is given to the subordinates so that they plan, motivate, control, and otherwise be responsible for their own actions.
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UNIT V - CONTROLLING
1. What are the characteristics of control? 1. Control process is universal 2. Control is continuous process
3. Control is action based
4. Control is forward looking.
2. What are the disadvantages of control? 1. Control is expensive and time-consuming process. 2. Human behaviour and employee morale also cannot be measured.
3. What is feedback control? Feedback control is the process of adjusting future action on basis of information about past performance.
4. What are the requirements for effective control? 1. The control should be economical 2. It must be simple
3. It should be flexible
4. It should be clear objectives
5. What are the modern techniques of control? 1. Management audit 2. Return on investment
3. PERT and CPM
6. What are the limitations of Budgeting? 1. Inaccuracy 2. Expenditure
3. Distortion of goals
7. What is Zero Base Budgets? Initially the budget is designed from a Zero base the main element is ZBB is future objective orientation.
8. What is Internal Audit? Internal audit is done by an internal auditor who is an employee of the organisation. He examines the objectives, policies, plans, procedures and performance of the management.
9. What are MIS Resources? 1. To provide the information up to date 2. To take effective decision making
3. To provide the right information available in the right form at the right time
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CS2411 OPERATING SYSTEMS
UNIT- I
Part A
1. What is an operating system?
An operating system is a program that manages the computer hardware. It acts as an
intermediate between users of a computer and the computer hardware. It controls and coordinates
the use of the hardware among the various application programs for the various users.
2. What is kernel?
The kernel is the central module of an Operating System (OS). It is the part of the operating
system that loads first, and it remains in main memory. It is important for the kernel to be as small as
possible while still providing all the essential services required by other parts of the operating system
and applications.
3. Define - Bootstrap Program (D-12)
Bootstrap program is used to start a computer. When powered up or rebooted the computer
needs to have an initial program to run. This bootstrap program finds the operating system on the
disk and loads that kernel into memory and jumps to an initial address to begin the operating system
execution. The full bootstrap program is stored in a partition called the boot blocks, at fixed location
on the disk. A disk that has boot partition is called boot disk or system disk.
4. What is meant by system calls? (D-11)
System calls provide the interface between a process and the operating system. When a
system call is executed, it is treated as software interrupt.
5. What is a process?
A process is a program in execution. It is an active entity and it includes the process stack,
containing temporary data and the data section contains global variables.
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6. What are schedulers?
A process migrates between the various scheduling queues throughout its life time. The OS
must select processes from these queues in some fashion. This selection process is carried out by a
scheduler.
7. What are the uses of queues, ready queues and device queues?
As a process enters a system they are put into a job queue. These queues consist of all jobs in
the system. When the processes that are residing in main memory are ready and waiting to execute
that are kept on a list called ready queue. The list of processes waiting for particular I/O devices kept
in the device queue.
8. What is meant by context switch? (D-12)
Switching the CPU to another process requires saving the state of the old process and loading
the saved state for the new process. This task is known as context switch.
9. What is co-operative process? (D-11)
A process is co-operating if it can affect or be affected by the other processes executing in the
system. Any process that share data with other process is a co-operating process.
10. Define - Thread Cancellation & Target Thread.
The thread cancellation is the task of terminating a thread before it is completed. A thread
that is to be cancelled is often referred to as the target thread. For example, if multiple threads are
concurrently searching through a database and one thread returns the result, the remaining threads
might be cancelled.
11. What is the use of inter process communication.
Inter process communication provides a mechanism to allow the co-operating process to
communicate with each other and synchronous their actions without sharing the same address space.
It provides a message passing system.
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12. What is a thread?
A thread otherwise called a Light Weight Process (LWP) is a basic unit of CPU utilization. It
comprises of a thread id, a program counter, a register set and a stack. It shares with other threads,
that are belonging to the same process its code section, data section, and operating system resources
such as open files and signals.
13. What are the benefits of multithreaded programming?
The benefits of multithreaded programming can be broken down into four major categories:
• Responsiveness
• Resource sharing
• Economy
• Utilization of multiprocessor architectures
14. Compare user threads with kernel threads.
User threads:
User threads are supported above the kernel and are implemented by a thread library
at the user level. Thread creation & scheduling are done in the user space, without kernel
intervention. Therefore they are fast to create and manage blocking system call which will cause
the entire process to block.
Kernel threads:
Kernel threads are supported directly by the operating system. Thread creations, scheduling
and management are done by the operating system. Therefore, they are slower to create &
manage compared to user threads. If the thread performs a blocking system call, the kernel can
schedule another thread in the application for execution.
15. What is the use of fork and exec system calls?
Fork is a system call by which a new process is created. Exec() will replace the contents of
the currently running process with the information from a program binary.
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UNIT II
1. Define − CPU Scheduling
CPU scheduling is the process of switching the CPU among various processes. CPU
scheduling is the basis of multi programming operating systems. By switching the CPU among
processes, the operating system can make the computer more productive.
2. What is preemptive and non preemptive scheduling? (D-12)
Under non preemptive scheduling once the CPU has been allocated to a process, the process
keeps the CPU until it releases the CPU either by terminating or switching to the waiting state. The
preemptive scheduling is prioritized. The highest priority process should always be the process that
is currently utilized.
3. What is a dispatcher?
A dispatcher is the module that gives the control of the CPU to the process selected by the short-term
scheduler.
This function involves:
• Switching context
• Switching to user mode
• Jumping to the proper location in the user program to restart that program
4. What is dispatch latency?
The time taken by the dispatcher to stop one process and start another running is known as
dispatch latency.
5. What are the various scheduling criteria for CPU scheduling?
The various scheduling criteria are:
• CPU utilization
• Throughput
• Turnaround time
• Waiting time
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6. Define - Throughput
Throughput in CPU scheduling is the number of processes that are completed per unit time.
For long processes, this rate may be one process per hour; for short transactions, throughput might be
10 processes per second.
7. What is turnaround time?
Turnaround time is the interval from the time of submission to the time of a process. It is the sum of
the periods spent waiting to get into memory, waiting in the ready queue, executing on the CPU, and
doing I/O.
8. What is critical section problem?
Consider a system consists of 'n' processes. Each process has segment of code called a critical
section, in which the process may be changing common variables, updating a table, writing a file.
When one process is executing in its critical section, no other process can be allowed to execute in its
critical section.
9. Define-Entry Section and Exit Section.
The critical section problem is to design a protocol that the processes can use to cooperate.
Each process must request permission to enter its critical section. The section of the code
implementing this request is the entry section. The critical section is followed by an exit section. The
remaining code is the remainder section.
10. What are semaphores? (M-10)
A semaphore 'S' is a synchronization tool which is an integer value that, apart from
initialization, is accessed only through two standard atomic operations; wait and signal. Semaphores
can be used to deal with the n-process critical section problem. It can also be used to solve various
synchronization problems.
11. Define- Busy Waiting and Spinlock
When a process is in its critical section, any other process that tries to enter its critical section
must loop continuously in the entry code. This is called as busy waiting and this type of semaphore is
also called a spinlock.
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12. Define Deadlock (M-10)
A process requests resources; if the resources are not available at that time, the process enters a wait
state. Waiting processes may never again change state, because the resources they have requested are
held by other waiting processes. This situation is called a deadlock.
13. Define Request Edge and Assignment Edge
A directed edge from process Pi to resource type Rj is denoted by PiàRj; it signifies that
process Pi requested an instance of resource type Rj and is currently waiting for that resource. A
directed edge from resource type Rj to process Pi is denoted by RjàPi, it signifies that an instance of
resource type has been allocated to a process Pi. A directed edge PiàRj is called a request edge. A
directed edge RjàPi is called an assignment edge.
14. What are the methods for handling deadlocks?
The deadlock problem can be dealt with in one of the three ways: a. Use a protocol to prevent
or avoid deadlocks, ensuring that the system will never enter a deadlock state. b. Allow the system to
enter the deadlock state, detect it and then recover. c. Ignore the problems to tally all together and
pretend that deadlocks never occur in the system.
15. Define Deadlock Prevention and Deadlock Avoidance
Deadlock prevention:
Deadlock prevention is a set of methods for ensuring that one of the four necessary
conditions like mutual exclusion, hold and wait, no preemption and circular wait cannot hold. By
ensuring that at least one of these conditions cannot hold, the occurrence of a deadlock can be
prevented.
Deadlock avoidance:
An alternative method for avoiding deadlocks is to require additional information about how
resources are to be requested. Each request requires the system to consider the resources currently
available. The resources currently allocated to each process, the future requests and releases of each
process to decide whether that could be satisfied or must wait to avoid a possible future deadlock.
16. What is banker’s algorithm?
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Banker’s algorithm is a deadlock avoidance algorithm that is applicable to a resource-allocation
system with multiple instances of each resource type.
The two algorithms used for its implementation are:
a. Safety algorithm: The algorithm for finding out whether or not a system is in a safe state.
b. Resource-request algorithm: if the resulting resource allocation is safe, the transaction is
completed and process Pi is allocated to its resources. If the new state is unsafe, Pi must wait
and the old resource-allocation state is restored.
UNIT-III
1. What is the main function of the memory-management unit?
The runtime mapping from virtual to physical addresses is done by a hardware device called a
Memory Management Unit (MMU).
2. Define - Dynamic Loading
Dynamic Loading is to obtain better memory-space utilization dynamic loading is used. With
dynamic loading, a routine is not loaded until it is called. All routines are kept on disk in a
relocatable load format. The main program is loaded into memory and executed. If the routine needs
another routine, the calling routine checks whether the routine has been loaded. If not, the relocatable
linking loader is called to load the program into memory.
3. Define - Dynamic Linking
Dynamic linking is similar to dynamic loading, rather than loading being postponed until
execution time, linking is postponed. This feature is usually used with system libraries, such as
language subroutine libraries. A stub is included in the image for each library-routine reference. The
stub is a small piece of code that indicates way to locate the appropriate memory-resident library
routine, or the wayS to load the library if the routine is not already present.
4. What are overlays? (M-10)
To enable a process to be larger than the amount of memory allocated to it, overlays are used.
The idea of overlays is to keep in memory only those instructions and data that are needed at a given
time. When other instructions are needed, they are loaded into space occupied previously by
instructions that are no longer needed.
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5. Define - Swapping.
A process needs to be in memory to be executed. However a process can be swapped
temporarily out of memory to a backing store and then brought back into memory for continued
execution. This process is called swapping.
6. What is virtual memory?
Virtual memory is a technique that allows the execution of processes that may not be
completely in memory. It is the separation of user logical memory from physical memory. This
separation provides an extremely large virtual memory, when only a smaller physical memory is
available.
7. What is Demand paging? (D-12)
Virtual memory is commonly implemented by demand paging. In demand paging, the pager
brings only those necessary pages into memory instead of swapping in a whole process. Thus, it
avoids reading into memory pages that will not be used anyway, decreasing the swap time and the
amount of physical memory needed.
8. Define – Lazy Swapper
Rather than swapping the entire process into main memory, a lazy swapper is used. A lazy
swapper never swaps a page into memory unless that page will be needed.
9. What is a pure demand paging? (M-10)
When starting execution of a process with no pages in memory, the operating system sets the
instruction pointer to the first instruction of the process, which is on a non-memory resident page, the
process immediately faults for the page. After this page is brought into memory, the process
continues to execute, faulting as necessary until every page that it needs is in memory. At that point,
it can execute with no more faults. This schema is pure demand paging.
10. Define - Effective Access Time
Let p be the probability of a page fault (0£p£1). The value of p is expected to be close to 0;
that is, there will be only a few page faults. The effective access time is effective access time = (1-p)
* ma + p* page fault time.ma: memory-access time
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11. What is the basic approach of page replacement? (D-11)
If no frame is free, find one that is not currently being used and free it. A frame can be freed
by writing its contents to swap space, and changing the page table to indicate that the page is no
longer in memory. Now the freed frame can be used to hold the page for which the process faulted.
12. What are the various page replacement algorithms used for page replacement?
The various page replacement algorithms used for page replacement are:
• FIFO page replacement
• Optimal page replacement
• LRU page replacement
• LRU approximation page replacement
• Counting based page replacement
• Page buffering algorithm.
13. What are the major problems to implement demand paging?
The major problems to implement demand paging are:
* Individual programs face extra latency when they access a page for the first time. So demand
paging may have lower performance than anticipatory paging algorithms such as prepaging.
* Programs running on low-cost, low-power embedded systems may not have a memory
management unit that supports page replacement.
* Memory management with page replacement algorithms becomes slightly more complex.
* Possible security risks, including vulnerability to timing attacks
14. What is a reference string?
An algorithm is evaluated by running it on a particular string of memory references and
computing the number of page faults. The string of memory reference is called a reference string.
15. Define - Secondary Memory
This memory holds those pages that are not present in main memory. The secondary memory is
usually a high speed disk. It is known as the swap evice, and the section of the disk used for this
purpose is known as swap space.
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UNIT-IV
PART-A
1. What is a file?
A file is a named collection of related information that is recorded on secondary storage. A
file contains either programs or data. A file has certain "structure" based on its type.
2. List out the various file attributes. (D-11)
A file has certain other attributes, which vary from one operating system to another, but
typically consist of these: Name, identifier, type, location, size, protection, time, date and user
identification.
3. What are the different accessing methods of a file?
The different types of accessing a file are:
• Sequential access: Information in the file is accessed sequentially
• Direct access: Information in the file can be accessed without any particular order.
• Other access methods: Creating index for the file, indexed sequential access method
(ISAM) etc.
4. What is directory? (M-10)
The directory records information-such as name, location, size, and type for all files on that
particular partition. The directory can be viewed as a symbol table that translates file names into their
directory entries.
5. What are the most common schemes for defining the logical structure of a directory?
The most common schemes for defining the logical structure of a directory
• Single-Level Directory
• Two-level Directory
• Tree-Structured Directories
• Acyclic-Graph Directories
• General Graph Directory
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6. Define - User File Directory and Master File Directory
In the two-level directory structure, each user has its own User File Directory (UFD). Each
UFD has a similar structure, but lists only the files of a single user. When a job starts the system's
Master File Directory (MFD) is searched. The MFD is indexed by the user name or account number,
and each entry points to the UFD for that user.
7. What is a path name?
Pathname is the path from the root through all subdirectories to a specified file. In a two-level
directory structure, a user name and a file name define a path name.
8. What are the various layers of a file system?
The file system is composed of many different levels. Each level in the design uses the feature of the
lower levels to create new features for use by higher levels.
• Application programs
• Logical file system
• File-organization module
• Basic file system
• I/O control
• Devices
9. What are the structures used in file-system implementation?
Several on-disk and in-memory structures that are used to implement a file system
. On-disk structure include
· Boot control block
· Partition block
· Directory structure used to organize the files
· File Control Block (FCB)
. In-memory structure include
· In-memory partition table
· In-memory directory structure
· System-wide open file table
· Per-process open table
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10. What are the functions of Virtual File System (VFS)? (D-12)
a. It separates file-system-generic operations from their implementation defining a clean VFS
interface. It allows transparent access to different types of file systems mounted locally.
b. VFS is based on a file representation structure, called a vnode. It contains a numerical
value for a network-wide unique file.The kernel maintains one vnode structure for each active file or
directory.
11. Define Seek Time and Latency Time (D-11)
The time taken by the head to move to the appropriate cylinder or track is called seek time.
Once the head is at right track, it must wait until the desired block rotates under the read-write head.
This delay is latency time.
12. What are the operations that can be performed on a directory?
The operations that can be performed on a directory are:
• Search for a file
• Create a file
• Delete a file
• Rename a file
• List directory
• Traverse the file system
13. What is the information associated with an open file?
Several pieces of information are associated with an open file which may be:
• File pointer
• File open count
• Disk location of the file
• Access rights
14. What are the various file operations?
The six basic file operations are :
• Creating a file
• Writing a file
• Reading a file
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UNIT-V
PART-A
1. What are the allocation methods of a disk space?
Methods of allocating disk space which are widely in use are
a. Contiguous allocation
b. Linked allocation
c. Indexed allocation
2 What are the advantages of Contiguous allocation?
The advantages are
a. Supports direct access
b. Supports sequential access
c. Number of disk seeks is minimal
3. What are the drawbacks of contiguous allocation of disk space?
The disadvantages are:
a. Suffers from external fragmentation
b. Suffers from internal fragmentation
c. Difficulty in finding space for a new file
d. File cannot be extended
e. Size of the file is to be declared in advance
4. What are the advantages of Linked allocation?
The advantages are:
a. No external fragmentation
b. Size of the file does not need to be declared
5. What are the disadvantages of linked allocation?
The disadvantages are:
a. Used only for sequential access of files.
b. Direct access is not supported
c. Memory space required for the pointers.
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6. Define - Rotational Latency and Disk Bandwidth (D-11)
Rotational latency is the additional time waiting for the disk to rotate the desired sector to the
disk head. The disk bandwidth is the total number of bytes transferred, divided by the time between
the first request for service and the completion of the last transfer.
7. Define - Buffering (M-10)
A buffer is a memory area that stores data while they are transferred between two devices or
between a device and an application. Buffering is done for three reasons which are: a. To cope with a
speed mismatch between the producer and consumer of a data stream b. To adapt between devices
that have different data transfer sizes and to support copy semantics for application I/O
8. Define - Caching
A cache is a region of fast memory that holds copies of data. Access to the cached copy is
more efficient than access to the original. Caching and buffering are distinct functions, but
sometimes a region of memory can be used for both purposes.
9. Define - Spooling (M-10)
A spool is a buffer that holds output for a device, such as printer, that cannot accept
interleaved data streams. When an application finishes printing, the spooling system queues the
corresponding spool file for output to the printer. The spooling system copies the queued spool files
to the printer one at a time.
10. What are the various disk-scheduling algorithms?
The various disk-scheduling algorithms are
a. First come first served scheduling
b. Shortest seek time first scheduling
c. SCAN scheduling
d. C-SCAN scheduling
f. LOOK scheduling
11. What is low-level formatting?
Before a disk can store data, it must be divided into sectors that the disk controller can read
and write. This process is called low-level formatting or physical formatting. Low-level formatting
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fills the disk with a special data structure for each sector. The data structure for a sector consists of a
header, a data area, and a trailer.
12. What is the use of boot block?
For a computer to start running when powered up or rebooted it needs to have an initial
program to run. This bootstrap program tends to be simple. It finds the operating system on the disk
loads that kernel into memory and jumps to an initial address to begin the operating system
execution. The full bootstrap program is stored in a partition called the boot blocks, at fixed location
on the disk. A disk that has boot partition is called boot disk or system disk.
13. What is sector sparing? (D-12)
Low-level formatting also sets aside spare sectors not visible to the operating system. The
controller can be told to replace each bad sector logically with one of the spare sectors. This scheme
is known as sector sparing or forwarding.
14. How is free space managed using bit vector implementation?
The free-space list is implemented as a bit map or bit vector. Each block is represented by 1 bit. If
the block is free, the bit is 1. If the block is allocated, the bit is 0.
15. What are the advantages of Indexed allocation?
The advantages are:
a. No external-fragmentation problem
b. Solves the size-declaration problems
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EI2311 BIOMEDICAL INSTRUMENTATION
UNIT – I PHYSIOLOGY AND TRANSDUCERS
1. What is meant by cell?
The basic living unit of the body is cell. The function of organs and other structure
of the body is understood by cell organization.
2. Write the abbreviation of RNA and DNA? 1. RNA –Ribo Nucleic Acid
2. DNA—De-Oxy Nucleic Acid
3. Write notes on resting potential, action potential and bio electric potential.
The membrane potential caused by the different concentration of ions is called
resting potential. It is caused by very rapid change of membrane permeability to sodium
ions followed by recovery period. The positive potential of the cell membrane during
excitation is called action potential. Certain systems of the body generate their own
monitoring signals conveying useful information about the functions they represent. Such
signals are bio electric potentials and are related to nerve conduction, brain activity, heart
beat etc.
4. What is meant by resting potential?
Equilibrium is reached with a potential difference across the membrane such that
there is negative on the inside and positive on the outside. This membrane potential caused
by the different concentration of ions is called resting potential.
5. What is meant by Action Potential?
Cell has a slightly positive potential on the inside due to imbalance of potassium
ions. This positive potential of the cell membrane during excitation is called action
potential and is about 20 mV.
6. List out the factors to be considered when any medical Instrument is designed.
Accuracy, frequency response, linearity, S/N ratio, stability and sensitivity
7. What is meant by electrode potential?
The voltage developed at an electrode-electrolyte interface is known as electrode
potential.
8. What is the purpose of electrode paste?
The electrode paste decreases the impedence of the contact, then the artifacts
resulting from the movement of the electrode or patient.
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9. Write the different types of electrodes.
The different types of electrodes are as follows:
1. Microelectrodes
2. Depth and needle electrodes
3. Surface electrodes
10. What are the different types of surface electrodes?
The different types of surface electrodes are as follows:
1. Metal Plate electrodes
2. Suction cup electrodes
3. Adhesive tape electrodes
4. Multi point electrodes
5. Floating electrodes
UNIT – II
ELECTRO – PHYSIOLOGICAL MEASUREMENTS
1. What is meant by defibrillator?
A defibrillator is an electronic device that creates a sustained myocardial
depolarization of a patient s heart in order to stop ventricular fibrillation or artial fibrillation.
2. What are the characteristics of a DC amplifier?
It may need balanced differential inputs giving a high common mode rejection ratio
(CMRR). It should have extremely good thermal and long term stability.
3. What are the merits of a DC amplifier?
The merits of a DC amplifier are
1. It is easy to calibrate at low frequencies.
2. It is able to recover from an overload condition unlike its AC counterpart.
4. Define – Transducers Transducers are defined as a device which when actuated, transforms energy from
one form to another. Generally, any physical parameters is converted into electrical form.
5. What are the types of transducers?
The types of transducers are
1. Electrical transducer
2. Mechanical transducer
6. Write the parameters that dictate the transducer capability
The parameters that dictate the transducer capability are
1. Linearity
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2. Repeatability
3. Resolution
4. Reliability
7. Define – Sensitivity
Sensitivity is defined as the electrical output per unit change in the physical
parameter. High sensitivity is generally desirable for a transducer.
8. What are the various types of electrical transducers?
The various types of electrical transducers are
1. Active
2. Passive
UNIT – III
NON-ELECTRICAL PARAMETER MEASUREMENTS
1. List out the parts of a transducer
The parts of a transducer are
1. Sensing element
2. Transduction element
2. Write the factors considered while selecting a transducer.
The factors that considered while selecting a transducer are
1. Operating range
2. Sensitivity
3. Frequency response & resonant frequency
4. Environmental compatibility
5. Minimum sensitivity Accuracy
6. Usage and ruggedness
7. Electrical parameters
3. What is meant by POT?
POT is a resistive potentiometer used for the purpose of voltage division. It consists
of a resistive element provided with a sliding contact called wiper.
4. Explain the working principle of a strain gauge.
Strain gauge works on the principle that the resistance of a conductor or a
semiconductor changes when strained. This property can be used for measurement of
displacement, force and pressure.
5. List out the different types of strain gauges.
The different types of strain gauges are
1. Un-bonded metal strain gauge
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2. Bonded metal wire strain gauge
3. Bonded metal foil strain gauge
4. Vacuum deposited thin metal film strain gauge
5. Sputter deposited thin metal strain gauge
6. Bonded semiconductor strain gauge
7. Diffused metal strain gauge
6. What is meant by rosette?
It is a combination of strain gauges to a single element strain gauge.
7. Write the working principles of variable inductance transducers. 1. Change of self inductance
2. Change of mutual inductance
3. Production of eddy currents
8. What is meant by LVDT?
It is the linear variable differential transformer which is used to translate the linear
motion into electrical signals. It consists of a single primary winding and 2 secondary
winding.
9. List out the advantages of LVDT.
The advantages of LVDT are
1. High range of displacement measurement
2. Friction & electrical isolation
3. Immunity from external effects
4. High I/p and high sensitivity
5. Ruggedness 6. Low hysterisis & low power consumption
UNIT – IV
MEDICAL IMAGING AND PMS
1. What is meant by digitizer?
It is a digital encoding transducer that enables a linear or rotary displacement to be
directly converted into digital form without intermediate forms of analog to digital (A/D)
conversion.
2. What are the classifications of pacemakers?
The classifications of pacemakers are
1. Fixed rate pacemakers
2. Ventricular Synchronous pacemakers
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3. Demand pacemakers
4. Atrial Synchronous pacemakers
3. What are the different methods of stimulation?
The different methods of stimulation are
1. External stimulation
2. Internal stimulation
4. What are the types of electrodes?
Devices that convert ionic potentials into electronic potentials are called electrodes.
There are three types of electrodes. They are as follows:
1. Micro electrode
2. Depth and needle electrode
3. Surface and needle electrode
5. What is meant by neuron and nerve fibers?
The basic Units of the nervous system is the neuron. A bundle of individual nerve
fibers is called a nerve .A neuron is a single cell with a cell body, called soma, one or more
inputs fibers called dendrites and a long transmitting fiber called axon. Both axons and
dendrites are called nerve fibers.
6. What are parts of central nervous system?
It consists of 1010 neurons. The brain consists of cerebrum, cerebellum and
brainstem. Cerebrums consist of two hemispheres and they are divided into frontal lobe,
occipital lobe and temporal lobe. Cerebellum consists of two hemispheres. They regulate the
coordination of muscular movements.
7. Write the parts that contain peripheral nervous system.
The nerve fibers outside the central nervous system are called peripheral nerves. It
consists of motor and sensory nerves.
8. Define – Circulatory System
It is defined as a type of transport system. It helps in supplying the oxygen and
digested food to different parts of our body and removing CO2 from the blood. The heart is
the center of the circulatory system.
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UNIT – V
ASSISTING AND THERAPEUTIC EQUIPMENTS
1. Define – Heart and Lung
Heart is defined as a pumping organ which eats regularly and continuously for years.
It beats seventy times a minute at rest. Contraction is systole and relaxation is diastole.
2. Define – Circulation and Respiration
From the engineering point of view, the circulation is a high resistance circuit
with a large pressure gradient between the arteries and veins. The exchange of any
gases in any biological process is termed as respiration
3. What is meant by transducer?
It is a device which detects or senses the bio signal and converts it in to an electrical
signal for bio signal processing
4. Define – Strain Gauge
It is an electrical device which is used to measure stress or pressure in terms of strain
using the principle of change of resistively due to mechanical stress
5. How are transducers classified?
They can be classified into different types based on the energy conversion, application
and so on. They are two types
Active transducer: A transducer that gives its output without the use of an excitation
voltage or modulation of a carrier signal is called an active transducer.
Passive transducer: A transducer that gives its output using an excitation voltage or
modulation of a carrier signal is called a passive transducer. Generally the active transducer
converts a non- electrical energy into electrical energy and converts an electrical into non –
electrical energy.
