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Power Systems Lab GRIET/EEE
1
POWER SYSTEMSLAB
___ YEAR ___ SEM
EEE
By
Dr. J. Sridevi
Gokaraju Rangaraju Institute of Engineering &
Technology
Bachupally
Power Systems Lab GRIET/EEE
2
GOKARAJU RANGARAJU INSTITUTE OF
ENGINEERING AND TECHNOLOGY
(Autonomous)
Bachupally , Hyderabad-500 072
CERTIFICATE
This is to certify that it is a record of practical work done in
the Power Systems Laboratory in ___ sem of __ year during
the year ________________________
Name:
Roll No:
Branch:EEE
Signature of staff member
Power Systems Lab GRIET/EEE
3
INDEX
S.No Date Topic Page no. Signature of
the Faculty
1. Tripping Characteristics of Fuse & MCB 9
2. Characteristics of Over current relay for
Phase fault
16
3. Characteristics of Over current relay for
Earth fault
24
4. Characteristics of Induction disc type relay 31
5. Characteristics of over load relay 37
6. Testing of Differential relay 42
7. Model of a Transmission Line with
Lumped parameters
47
8. Characteristics of Over voltage Relay 52
9. Characteristics of Under voltage Relay 58
10. Zones Protection 64
11. Short circuit analysis 70
12. Tripping sequence of protective devices 75
13. Testing of Negative sequence Relay 80
Power Systems Lab GRIET/EEE
4
ETAP SOFTWARE INTRODUCTION
ETAP stands for Electrical Transient Analysis Program, This amazing software suite covers a
wide range of electrical engineering domains; from software for network analysis to power
distribution. The wide range of software modules from ETAP are one of the most beneficial and
effective for electrical engineers. The Arc flash analysis software from ETAP allows engineers to
use simulation models to identify and mitigate arc flash hazards in the electrical power system
and other arc flash related issues.
Here we are using this software to analyse basic operation of power system during transients,
normal operation and fault conditions without actually interfacing with practical power system.
The main parts a power system we come across are as follows
1. Power Grid
2. Bus bar
3. Power Cable
4. Transformer
5. Circuit breaker
6. Relays
7. Fuse
8. Load(motor)
The detailed meaning of them is given below
1. Power Grid: An electrical grid is an interconnected network for delivering electricity to
consumers. It consists of generating stations that produce electrical power, high voltage
transmission lines that carry electrical power from distance sources to demand centres
Power Systems Lab GRIET/EEE
5
and distribution lines that connect individual consumers. It looks as shown below in
ETAP.
2. Bus bar: A bus as regard to the power system is an electrical junction (node) .It is a strip
or bar of copper, brass or aluminium that conducts electricity within a
switchboard, distribution board, substation, battery bank, or other electrical apparatus. Its
main purpose is to conduct a substantial current of electricity.
3. Power Cable: A power cable is an assembly of one or more electrical conductors,
usually held together with an overall sheath. The assembly is used for transmission
of electrical power. Power cables may be installed as permanent wiring within buildings,
buried in the ground, run overhead, or exposed. In ETAP it looks as:
4. Transformer: Electrical power transformer is a static device which transforms
electrical energy from one circuit to another without any direct electrical connection and
with the help of mutual induction between two windings. It transforms power from one
circuit to another without changing its frequency but may be in different voltage level. It
steps up or steps down the voltage by changing the number of windings in primary and
secondary.
5. Circuit breaker: A circuit breaker is an automatically
operated electrical switch designed to protect an electrical circuit from damage caused by
Power Systems Lab GRIET/EEE
6
overload or short circuit. Its basic function is to detect a fault condition and interrupt
current flow. Unlike a fuse, which operates once and then must be replaced, a circuit
breaker can be reset (either manually or automatically) to resume normal operation.
Mainly here we come across two types of CB’s. They are
High Voltage Circuit Breaker (HVCB): High-voltage breakers are nearly
always solenoid-operated, with current sensing protective relays operated
through current transformers of about 72.5KV or higher.
Low Voltage Circuit Breaker (LVCB): Low-voltage (less than 1,000 VAC) types
are common in domestic, commercial and industrial application.
6. Relays: A relay is an electrically operated switch. Many relays use an electromagnet to
mechanically operate a switch. Relays are used where it is necessary to control a circuit
by a low-power signal (with complete electrical isolation between control and controlled
circuits), or where several circuits must be controlled by one signal. There are mainly
relays we use in ETAP. They are Over Current Relay, In-line Overload Protection Relay,
Voltage Relay, Differential Relay, Frequency Relay.
i. In-line Overload Relay:
A relay that opens a circuit when the load in the circuit exceeds a preset value, in
order to provide overload protection; usually respondsto excessive current, but ma
y respond to excessive values of power, temperature, or other quantitiesAlso kno
Power Systems Lab GRIET/EEE
7
wn as overload release. In ETAP it is denoted by 49 which is ANSI code for In-
line overload relay.
ii. Over Current Relay:
A digital over current relay is a type of protective relay which operates when the
load current exceeds a pickup value. The ANSI device number is 50 for an
instantaneous over current (IOC) and 51 for a time over current (TOC). In a
typical application the over current relay is connected to a current transformer and
calibrated to operate at or above a specific current level. When the relay operates,
one or more contacts will operate and energize to trip (open) a circuit breaker.
iii. Voltage Relay: A
relay which operates when the system voltage when the system falls below or
above a certain preset value. For an under voltage relay the ANSI code is 27,
which is used as a standard in ETAP.
iv. Differential Relay:
A relay which responds to a difference in two voltages or currents. For example,
such a relay may have two coils and only respond when the respective currents of
said coils vary beyond a specified amount. It’s denoted by the ANSI code no.87 in
ETAP.
v. Frequency Relay:
Relay which functions at a predetermined value of frequency; may be an over-
frequency relay, an under-frequency relay, or a combinationof both. It is denoted
by the ANSI code no. 81 in ETAP to determine it’s specific function.
7. Fuse: A fuse is a type of low resistance resistor that acts as a sacrificial device to
provide overcurrent protection, of either the load or source circuit. Its essential
component is a metal wire or strip that melts when too much current flows through it,
interrupting the circuit that it connects. Short circuits, overloading, mismatched loads, or
Power Systems Lab GRIET/EEE
8
device failure are the prime reasons for excessive current. Fuses are an alternative
to circuit breakers. It can be seen in ETAP as:
8. Load (Motor):
The electric power delivered by a power source to a power user. If variations in voltage a
re small, load can becharacterized by magnitude of current. The term “load” is also often
applied to the device consuming the electric power—that is, to a piece of
equipment, such as a motor or a lighting device. In ETAP we come across mainly
Induction Motor, Synchronous Motor and Lumped load
Power Systems Lab GRIET/EEE
9
Date: Experiment-1
TRIPPING CHARACTERISTICS OF FUSE & MCB
AIM:To study the Time current characteristics of FUSE and MCB for given network.
SOFTWARE USED: ETAP Software
THEORY:
Time Current Characteristics of protective devices:
Time is plotted on the vertical axis and current is plotted on the horizontal axis of all time-
current characteristic curves. Log-log type graph paper is used to cover a wide range of times
and currents. Characteristic curves are arranged so that the area below and to the left of the
curves indicate points of "no operation,” and the area above and to the right of the curves
indicate points of "operation." The procedure involved in applying characteristic curves to a
coordination study is to select or set the various protective devices so that the characteristic
curves of series devices from the load to the source are located on a composite time-current
graph from left to right with no overlapping of curves. The result is a set of coordinated curves
on one composite time current graph.
The MCB has some advantages compared to fuse
1. It automatically switches off the electrical circuit during abnormal condition of the network
means in over load condition as well as faulty condition. The fuse does not sense but miniature
circuit breaker does it in more reliable way. MCB is much more sensitive to over current than
fuse.
2. Another advantage is, as the switch operating knob comes at its off position during tripping,
the faulty zone of the electrical circuit can easily be identified. But in case of fuse, fuse wire
should be checked by opening fuse grip or cutout from fuse base, for confirming the blow of fuse
wire.
3. Quick restoration of supply can not be possible in case of fuse as because fuses have to be
rewirable or replaced for restoring the supply. But in the case of MCB, quick restoration is
possible by just switching on operation.
Power Systems Lab GRIET/EEE
10
4. Handling MCB is more electrically safe than fuse.
Because of to many advantages of MCB over fuse units, in modern low voltage electrical
network, miniature circuit breaker is mostly used instead of backdated fuse unit.
Only one disadvantage of MCB over fuse is that this system is more costlier than fuse unit
system.
Working Principle Miniature Circuit Breaker
There are two arrangement of operation of miniature circuit breaker. One due to thermal
effect of over current and other due to electromagnetic effect of over current. The thermal
operation of miniature circuit breaker is achieved with a bimetallic strip whenever continuous
over current flows through MCB, the bimetallic strip is heated and deflects by bending. This
deflection of bimetallic strip releases mechanical latch. As this mechanical latch is attached with
operating mechanism, it causes to open the miniature circuit breaker contacts. But during short
circuit condition, sudden rising of current, causes electromechanical displacement of plunger
associated with tripping coil or solenoid of MCB. The plunger strikes the trip lever causing
immediate release of latch mechanism consequently open the circuit breaker contacts.
Power Systems Lab GRIET/EEE
11
PARAMETERS:
SI.NO
COMPONENT
MANUFACTURER
RATING
OTHER
PARAMETERS TO
BE SPECIFIED
1.
2.
3.
4.
5.
6.
7.
8.
9.
Power Grid
Buses
Bus1
Bus2
Bus3
CT1
CT2
OCR
Cable
Fuse
Transformer
CB1
CB2
Synchronous
motor
---
----
----
----
ABB
GE Multilin
735/737
(Lib-220)
ICEA
Seimens
A500-2.54KV
Lib 1HP
0.46KV(MTR)
200MVASc
12.47kV
12.47KV
12.47KV
300:5
300:5
1000KVA
Pri-12.47KV
Sec-0.48KV
POWER-
1000KVA
Siemen Allis
LA-1600A
Siemens
Static-Trip III
2HP
0.46KV
X/R=5
1.Add circuit breaker.
2.choose any type of
relay
TCC KA
Phase-12.47
1.length-100
Tolerance-0
Impedance –typical
Z&X/R ratio
Power Systems Lab GRIET/EEE
12
ETAP NETWORK DIAGRAM:
PROCEDURE:
Open the ETAP software in the pc.
On the right hand side of the software equipments are present.
Construct the circuit as shown in circuit diagram in “Edit mode” tab.
Click on the star protective devices icon present at the top of the edit mode.
Then select a part of the circuit and click on the star view at right.
The graphs are obtained and studied
Power Systems Lab GRIET/EEE
13
ETAP Simulation diagram:
Power Systems Lab GRIET/EEE
14
TIME CURRENT CHARACTERISTIC CURVES:
Power Systems Lab GRIET/EEE
15
Result:
Signature of the faculty
Power Systems Lab GRIET/EEE
16
Date: Experiment-2
CHARACTERISTICS OF OVER CURRENT RELAY FOR PHASE FAULT
AIM: To study the characteristics of over current realy for phase fault
APPARATUS: Over current relay
Auxiliary supply kit (Step-down Transformer-230/24V, Bridge rectifier, filter)
Auto transformer (0-230v, 2A)
Ammeter (0-2A)
Rheostat (110Ω, 1.8A)
THEORY:
The function of a relay is to detect abnormal conditions in the system and to initiate through
appropriate circuit breakers the disconnection of faulty circuits so that interference with the
general supply is minimized. Relays are of many types. Some depend on the operation of an
armature by some form of electromagnet. A very large number of relays operate on the induction
principle. When a relay operates it closes contacts in the trip circuit .The passage of current in
the coil of the trip circuit actuates the plunger, which causes operation of the circuit breaker,
disconnecting the faulty system.
OVER CURRENT PROTECTION:
The protective relaying which responds to a rise in current flowing through the protected element
over a pre-determined value is called 'overcurrent protection' and the relays used for this purpose
are known as overcurrent relays. Earth fault protection can be provided with normal overcurrent
relays, if the minimum earth fault current is sufficient in magnitude. The design of a
comprehensive protection scheme in a power system requires the detailed study of time-current
characteristics of the various relays used in the scheme. Thus it is necessary to obtain the time
current characteristics of these relays. The overcurrent relay works on the induction principle.
The moving system consists of an aluminum disc fixed on a vertical shaft and rotating on two
jeweled bearings between the poles of an electromagnet and a damping magnet. The winding of
the electromagnet is provided with seven taps (generally0, which are brought on the front panel,
and the required tap is selected by a push-in -type plug. The pick-up current setting can thus be
Power Systems Lab GRIET/EEE
17
varied by the use of such plug multiplier setting. The operating time of all overcurrent relays
tends to become asymptotic to a definite minimum value with increase in the value of current.
This is an inherent property of the electromagnetic relays due to saturation of the magnetic
circuit. By varying the point of saturation, different characteristics can be obtained and these are
1. Definite time
2. Inverse Definite Minimum Time (IDMT)
3. Very Inverse
4. Extremely Inverse
Principle:
Overcurrent protection is practical application of magnitude relays since it picks up when the
magnitude of current exceeds some value (setting value). Overcurrent relays can be used to
protect practically any power system elements, i.e. transmission lines, transformers, generators,
or motors. As an example, a radial transmission line can be used. For a fault within the zone of
protection, the fault current is smallest at the end of the line and greatest at the relay end. If the
minimum fault current possible within the zone of protection is greater than the maximum
possible load current, it would be possible to define the operating principle as follows:
Where I is the current in the relay and is Ip the pickup setting of the relay.
Instantaneous overcurrent relays :
Its operation criterion is only current magnitude (without time delay). This type is applied to the
outgoing feeders.
Characteristics of instantaneous over current Relay
Power Systems Lab GRIET/EEE
18
Definite Time Overcurrent Relays :
In this type, two conditions must be satisfied for operation (tripping), current must exceed the
setting value and the fault must be continuous at least a time equal to time setting of the relay.
Modern relays may contain more than one stage of protection each stage includes each own
current and time setting.
Characteristics of definite time over current Relay
Definite time overcurrent relay is the most applied type of over current. It is used as:
1. Back up protection of distance relay of transmission line with time delay.
2. Back up protection to differential relay of power transformer with time delay.
3. Main protection to outgoing feeders and bus couplers with adjustable time delay setting.
Inverse Time Overcurrent Relays
In this type of relays, operating time is inversely changed with current. So, high current will
operate overcurrent relay faster than lower ones. There are standard inverse, very inverse and
extremely inverse types
Characteristics of inverse time over current Relay
Power Systems Lab GRIET/EEE
19
CIRCUIT DIAGRAM:
Experimental procedure:
1. Study the construction of the relay and identify the various parts.
2. Set the pick-up value of the current marked 1 A(100 % f. l current)
3. Set the Time Multiplier Setting (TMS) initially at 1.0.
4. Adjust the load current to about 1.8 times the f.l current. Record the time taken for the
overload condition.
5. Vary the value of the load current in steps and record the time taken for the operation of
the relay in each case with the help of the timer.
6. Repeat steps 5 and 6 for TMS values of 0.2, 0.4,0.6 and 0.8.
7. Repeat the above experiment with different pick up current values using the plug setting
bridge.
Power Systems Lab GRIET/EEE
20
Tabular form-Range of Experimental values:
Pick-up current = 1 Amps
IP - Current setting: 10% = 0.1A
S.No Current(A) Current(A)
times the
plug setting
multiplier
Tp- Operating time in sec. for TMS of
1.0 0.8 0.6 0.4 0.2
1 0.12 1.2 38 30.4 22.8 15.2 7.6
2 0.13 1.3 28 22.4 16.8 11.2 5.6
3 0.14 1.4 22 17.6 13.2 8.8 4.4
4 0.16 1.6 17 13.6 10.2 6.8 3.4
5 0.18 1.8 14 11.2 8.4 5.6 2.8
Tabular form-practical values:
Pick-up current = 1 Amps
IP - Current setting :10%
S.No Current(A) Current(A)
times the
plug setting
multiplier
Tp- Operating time in sec. for TMS of
1.0 0.8 0.6 0.4 0.2
1
2
3
4
5
Power Systems Lab GRIET/EEE
21
Model graph-Characteristics of over current relay
0
5
10
15
20
25
30
35
40
0 0.5 1 1.5 2
TIME(Sec)
PSM
TMS-1 TMS-0.8 TMS-0.6
Power Systems Lab GRIET/EEE
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Power Systems Lab GRIET/EEE
23
RESULT:
Signature of the faculty
Power Systems Lab GRIET/EEE
24
Date: Experiment-3
CHARACTERISTICS OF OVER CURRENT RELAY FOR EARTH FAULT
Aim: To study the characteristics of over current relay for earth fault
Apparatus: Earth Fault relay
Auxiliary supply kit (Step-down Transformer-230/24V, Bridge rectifier, filter)
Auto transformer (0-230v, 2A)
Ammeter (0-2A)
Rheostat (110Ω, 1.8A)
Theory:
The function of a relay is to detect abnormal conditions in the system and to initiate through
appropriate circuit breakers the disconnection of faulty circuits so that interference with the
general supply is minimized. Relays are of many types. Some depend on the operation of an
armature by some form of electromagnet. A very large number of relays operate on the induction
principle. When a relay operates it closes contacts in the trip circuit .The passage of current in
the coil of the trip circuit actuates the plunger, which causes operation of the circuit breaker,
disconnecting the faulty system.
Overcurrent Protection
The protective relaying which responds to a rise in current flowing through the protected element
over a pre-determined value is called 'overcurrent protection' and the relays used for this purpose
are known as overcurrent relays. Earth fault protection can be provided with normal overcurrent
relays, if the minimum earth fault current is sufficient in magnitude. The design of a
comprehensive protection scheme in a power system requires the detailed study of time-current
characteristics of the various relays used in the scheme. Thus it is necessary to obtain the time
current characteristics of these relays. The overcurrent relay works on the induction principle.
The moving system consists of an aluminum disc fixed on a vertical shaft and rotating on two
jeweled bearings between the poles of an electromagnet and a damping magnet. The winding of
the electromagnet is provided with seven taps (generally0, which are brought on the front panel,
and the required tap is selected by a push-in -type plug. The pick-up current setting can thus be
Power Systems Lab GRIET/EEE
25
varied by the use of such plug multiplier setting. The operating time of all overcurrent relays
tends to become asymptotic to a definite minimum value with increase in the value of current.
This is an inherent property of the electromagnetic relays due to saturation of the magnetic
circuit. By varying the point of saturation, different characteristics can be obtained and these are
1. Definite time
2. Inverse Definite Minimum Time (IDMT)
3. Very Inverse
4. Extremely Inverse
Principle:
Overcurrent protection is practical application of magnitude relays since it picks up when
the magnitude of current exceeds some value (setting value). Overcurrent relays can be used to
protect practically any power system elements, i.e. transmission lines, transformers, generators,
or motors. As an example, a radial transmission line can be used. For a fault within the zone of
protection, the fault current is smallest at the end of the line and greatest at the relay end. If the
minimum fault current possible within the zone of protection is greater than the maximum
possible load current, it would be possible to define the operating principle as follows:
Where I is the current in the relay and is Ip the pickup setting of the relay.
Protection against earth faults can be obtained by using a relay that responds only to the
residual current of the system, since a residual component exists only when fault current flows to
earth. The earth-fault relay is therefore completely unaffected by load currents, whether balanced
or not, and can be given a setting which is limited only by the design of the equipment and the
presence of unbalanced leakage or capacitance currents to earth. This is an important
consideration if settings of only a few percent of system rating are considered, since leakage
currents may produce a residual quantity of this order.
Power Systems Lab GRIET/EEE
26
Circuit Diagram:
Experimental procedure:
1. Study the construction of the relay and identify the various parts.
2. Set the pick-up value of the current marked 1 A(100 % f. l current)
3. Set the Time Multiplier Setting (TMS) initially at 1.0.
4. Adjust the load current to about 1.8 times the f.l current. Record the time taken for the
overload condition.
5. Vary the value of the load current in steps and record the time taken for the operation of
the relay in each case with the help of the timer.
6. Repeat steps 5 and 6 for TMS values of 0.2, 0.4,0.6 and 0.8.
7. Repeat the above experiment with different pick up current values using the plug setting
bridge.
Power Systems Lab GRIET/EEE
27
Tabular form-Range of Experimental values:
Pick-up current = 1 Amps
IE - Current setting: 10% = 0.1A
S.No Current(A) Current(A)
times the
plug setting
multiplier
Tp- Operating time in sec. for
TMS of
1.0 0.8 0.6 0.4
1 0.12 1.2 35 26 20 12
2 0.13 1.3 20 16 10 7
3 0.14 1.4 14 11 8 5
4 0.16 1.6 12 9 7 4
5 0.18 1.8 10 8 6 3
Tabular form-practical values:
Pick-up current = 1 Amps
IE - Current setting :
S.No Current(A) Current(A)
times the
plug setting
multiplier
Tp- Operating time in sec. for
TMS of
1.0 0.8 0.6 0.4
1
2
3
4
5
Power Systems Lab GRIET/EEE
28
Model graph-Characteristics of Earth fault relay
0
5
10
15
20
25
30
35
40
0 0.5 1 1.5 2
TIME(Sec)
PSM
TMS-1 TMS-0.8 TMS-0.6
Power Systems Lab GRIET/EEE
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Power Systems Lab GRIET/EEE
30
RESULT:
Signature of the faculty
Power Systems Lab GRIET/EEE
31
Date: Experiment-4
CHARACTERISTICS OF INDUCTION DISC TYPE RELAY
Aim: To study the characteristics of induction disc type relay
Apparatus: Induction disc type relay
Auxiliary supply kit (Step-down Transformer-230/24V, Bridge rectifier, filter)
Auto transformer (0-230v, 20A)
Ammeter (0-20A)
Rheostat (110Ω, 1.8A)
Theory:
The function of a relay is to detect abnormal conditions in the system and to initiate
through appropriate circuit breakers the disconnection of faulty circuits so that interference with
the general supply is minimized. Relays are of many types. Some depend on the operation of an
armature by some form of electromagnet. A very large number of relays operate on the induction
principle. When a relay operates it closes contacts in the trip circuit .The passage of current in
the coil of the trip circuit actuates the plunger, which causes operation of the circuit breaker,
disconnecting the faulty system.
Induction disc type relay:
The electromagnetic induction disc relay is frequently used where the time of relay operation
should depend upon the amount of an overcurrent. The relay is essentially a small induction
motor. This is probably the most widely used protective relay in the industry. It starts to turn
when the current exceeds a (previously selected) threshold current, and rotates faster as the
current increases. This relay has one set of stationary contacts and one set which moves as the
disc turns. The distance which the disc must travel to close the contacts is adjusted by setting the
position of the time dial control. The magnitude of current which initiates disc movement is set
by the choice of the tap on the current coil. The results is that relay contact operation is
Power Systems Lab GRIET/EEE
32
dependent upon the tap and the time dial settings. The relay timing can be varied from a few
cycles to as long as 30 seconds.
An induction relay works only with alternating current. It consists of an electromagnetic system
which operates on a moving conductor, generally in the form of a disc or cup, and functions
through the interaction of electromagnetic fluxes with the parasitic Fault currents which are
induced in the rotor by these fluxes. These two fluxes, which are mutually displaced both in
angle and in position, produce a torque.
Induction disc type Relay
Basic torque/current equation
T= Κ1.Φ1.Φ2 .sin θ
Where Φ1 and Φ2 are the interacting fluxes and θ is the phase angle between Φ1 and Φ2. It
should be noted that the torque is a maximum when the fluxes are out of phase by 90º, and zero
when they are in phase.
The relay's primary winding is supplied from the power systems current transformer via a plug
bridge, which is called the plug setting multiplier (psm). Usually seven equally spaced tappings
or operating bands determine the relays sensitivity. The primary winding is located on the upper
electromagnet. The secondary winding has connections on the upper electromagnet that are
energised from the primary winding and connected to the lower electromagnet. Once the upper
and lower electromagnets are energised they produce eddy currents that are induced onto the
metal disc and flow through the flux paths. This relationship of eddy currents and fluxes creates
torque proportional to the input current of the primary winding, due to the two flux paths been
Power Systems Lab GRIET/EEE
33
out of phase by 90°.A restraining spring forces the disk to rotate in the direction that opens the
trip contacts while current creates operating torque to close the contacts. The net positive torque
closes the contacts. The IPU relay setting fixes the value of the pickup current. When the current
applied to the relay equals the pickup current, the contact closing torque just equals the
restraining torque and the disk will not move regardless of its position. If the applied current
increases above the pickup current, the disk will begin to rotate so that the trip contacts come
closer together
Wiring Diagram:
Power Systems Lab GRIET/EEE
34
Experimental procedure:
1. Study the construction of the relay and identify the various parts.
2. Set the pick-up value of the current as 2.5A
3. Adjust the load current to about 1.3 times the full load current. Record the time taken for
the overload condition.
4. Vary the value of the load current in steps and record the time taken for the operation of
the relay in each case with the help of the timer.
5. Repeat the above experiment with different pick up current values.
Tabular form-Range of Experimental values:
Pick-up current = 2.5 Amps
S.No Current(A) Current(A)
times the
plug setting
multiplier
Operating
Time in
seconds
1
2
3
4
5
Power Systems Lab GRIET/EEE
35
Model graph :Characteristics of induction disc type relay
0
5
10
15
20
25
30
35
40
0 0.5 1 1.5 2
TIME(Sec)
PSM
TMS-1 TMS-0.8 TMS-0.6
Power Systems Lab GRIET/EEE
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RESULT:
Signature of the faculty
Power Systems Lab GRIET/EEE
37
Date: Experiment-5
CHARACTERISTICS OF OVER LOAD RELAY
AIM:To study the characteristics of over load relay.
SOFTWARE USED: ETAP Software
Theory:
Overload relays protect a motor by sensing the current going to the motor. Many of these use
small heaters, often bi-metallic elements that bend when warmed by current to the motor.When
current is too high for too long, heaters open the relay contacts carrying current to the coil of the
contactor. When the contacts open, the contactor coil de-energizes, which results in an
interruption of the main power to the motor. These contacts do not affect control power.
Overload relays and their heaters belong to one of three classes, depending on the time it takes
for them to respond to an overload in the motor. The overload relay itself will have markings to
indicate which class it belongs to. These include Class 10, 20, and 30. The class number
indicates the response time (in seconds). An unmarked overload relay is always Class 20.
Typical NEMA-rated overload relays are Class 20, but you can adjust many of them about 15%
above or below their normal trip current. IEC relays are usually Class 10, and you can usually
adjust them to 50% above their normal trip current.
Power Systems Lab GRIET/EEE
38
PARAMETERS:
SI.NO
COMPONENT
MANUFACTURER
RATING
OTHER
PARAMETERS TO
BE SPECIFIED
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Power Grid
Buses
Bus1
Bus2
Bus3
CT1
CT2
OCR
Cable
Fuse
Transformer
CB1
CB2
Induction motor
Thermal Over
load Heater
---
----
----
----
ABB
GE Multilin
735/737
(Lib-220)
ICEA
Seimens
A500-2.54KV
MTR Lib 1HP 0.46KV
General Electric
200MVASc
12.47kV
12.47KV
12.47KV
300:5
300:5
1000KVA
Pri-12.47KV
Sec-0.48KV
POWER-
1000KVA
Siemen Allis
LA-1600A
Siemens
Static-Trip III
2HP
0.46KV
0.48 kv
X/R=5
1.Add circuit breaker.
2.choose any type of
relay
TCC KA
Phase-12.47
1.length-100
Tolerance-0
Impedance –typical
Z&X/R ratio
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ETAP Network Diagram:
PROCEDURE:
Open the ETAP software in the pc.
On the right hand side of the software equipments are present.
Construct the circuit as shown in circuit diagram in “Edit mode” tab.
Click on the star protective devices icon present at the top of the edit mode.
Then select a part of the circuit and click on the star view at right.
The graphs are obtained and studied.
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TIME CURRENT CHARACTERISTIC CURVES:
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RESULT:
Signature of the faculty
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Date: Experiment-6
TESTING OF DIFFERENTIAL RELAY
Aim: To study the operation of Differential Relay
Apparatus: Differential Relay
Auxiliary supply kit (Step-down Transformer-230/24V, Bridge rectifier, filter)
Auto transformer (0-230v, 2A)-2 No.s
Ammeter (0-2A)-2 No.s
Rheostat (110Ω, 1.8A) -2 No.s
Theory:
The relay which is used to checks the difference between the output and input currents
for power system current in known as differential relay. The difference amongst the currents may
also be in phase angle or in magnitude or in eachthe angle and magnitude variations must be
zero. In case there's a difference which difference go beyond some value, the relay can work and
interconnected electrical fuse can disconnect.
Principle Operation of differential relay:
Consider a power transformer with transformation magnitude (ratio) relation 1:1 and (Y/Y)
connection and therefore the CT1 and CT2 ensure a similar transformation magnitude relation as
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shown. The current flows within the primary side and secondary side of power transformer are
equal, presumptuous ideal power transformer. The secondary current I1 and I2 are same in
magnitude and reverse in direction. Therefore, the net current within the differential coil is nil at
load situation (without any fault), and therefore the relay won't operate.
External Fault Condition in Differential Relay:
Assigning the previous one the power transformer with an external fault F is shown in figure.
During this case the 2 currents I1, and I2 can increase to terribly high magnitudes values however
there's no modification in phase angle. Hence, net current within the differential coil continues to
be zero and therefore the relay won't operate.
Internal Fault Condition in Differential Relay:
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An internal fault F is shown in this figure. Now, there are 2 anticipated conditions:
There’s other supply to feed the fault thus I2P includes a nonzero value Idiff = I1S + I2S which can
be terribly high and sufficient to function the differential relay.
Radial system, I2P = 0. So, Idiff = I1S and additionally the relay can work and disconnect the
breaker.
Circuit Diagram
Procedure:
1. Study the construction of the relay and identify the various parts.
2. Set the Bias current and current setting.
3. With zero bias current (ammeter A2=0), inject operate current in to phase A. When the
relay operates, shown bythe LED "Trip" illuminating, record the value of the current
indicated on ammeter A1.
4. Repeat the test with increasing bias currents up to 2times the relay rating.
5. Record the results in Table.
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Model Tabular Form:
Initial
settings
Bias
settings
Bias current Ammeter A2 multiples of rated current in
0 1 1.5 2 2.5
Operate current, ammeter A1 Amps
10% 10% 0.1 0.11 0.16 0.21 2.26
20% 20% 0.2 0.21 0.33 0.44 0.56
30% 30% 0.3 0.35 0.53 0.71 0.88
40% 40% 0.4 0.5 0.75 1 1.25
50% 50% 0.5 0.67 1 1.33 1.67
- 70% 0.5 0.86 1.29 1.71 2.14
- 80% 0.5 1.08 1.62 2.15 2.69
Tabular form :practical readings
Intial
settings
Ammeter A2 multiples of rated current in
Operate current, ammeter A1 Amps
10%
20%
30%
40%
50%
-
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RESULT:
Signature of the faculty
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Date: Experiment-7
MODEL OF A TRANSMISSION LINE WITH LUMPED PARAMETERS
AIM:To run the load flow for a given transmission line network
SOFTWARE USED: ETAP Software
Theory:
The power-flow study, or load-flow study, is a numerical analysis of the flow of electric power
in an interconnected system. A power-flow study usually uses simplified notation such as a one-
line diagram and per-unit system, and focuses on various aspects of AC power parameters, such
as voltages, voltage angles, real power and reactive power. It analyzes the power systems in
normal steady-state operation.
Power-flow or load-flow studies are important for planning future expansion of power systems
as well as in determining the best operation of existing systems. The principal information
obtained from the power-flow study is the magnitude and phase angle of the voltage at each bus,
and the real and reactive power flowing in each line.
The goal of a power-flow study is to obtain complete voltage angle and magnitude information
for each bus in a power system for specified load and generator real power and voltage
conditions.[2] Once this information is known, real and reactive power flow on each branch as
well as generator reactive power output can be analytically determined. Due to the nonlinear
nature of this problem, numerical methods are employed to obtain a solution that is within an
acceptable tolerance.
The solution to the power-flow problem begins with identifying the known and unknown
variables in the system. The known and unknown variables are dependent on the type of bus. A
bus without any generators connected to it is called a Load Bus. With one exception, a bus with
at least one generator connected to it is called a Generator Bus. The exception is one arbitrarily-
selected bus that has a generator. This bus is referred to as the slack bus.
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PARAMETERS:
SI.NO
COMPONENT
MANUFACTURER
RATING
OTHER
PARAMETERS TO
BE SPECIFIED
1.
2.
3.
4.
5.
6.
7.
Buses
Bus1
Bus2
Bus3
Impedances
Z12
Z12
Z12
Sych.Generator 1
Sych.Generator 2
Lumped Load
----
----
----
-----
-----
-----
-----
-----
-----
100KV
100KV
100KV
Percentage base
KV-100kv
Percentage base
KV-100kv
Percentage base
KV-100kv
100KV,
250 MW
100KV,
250 MW
400MW,471MVA
R=2,X=4,Y=0
R=1,X=3,Y=0
R=1.25,X=2.5,Y=0
Reference or Slack
bus
Generator bus
Var limits:200&-100
Conventional model,
Rated 100kv
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ETAP Network Diagram: Transmission line model
PROCEDURE:
Open the ETAP software in the pc.
On the right hand side of the software equipments are present.
Construct the circuit as shown in circuit diagram in “Edit mode” tab.
Run the load flow analysis for a given network.
Get the power flow values at each bus.
And get the results through load flow result analyser
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SIMULATION RESULTS:
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RESULT:
Signature of the faculty
Power Systems Lab GRIET/EEE
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Date: Experiment-8
CHARACTERISTICS OF OVER VOLTAGE RELAY
AIM: To study the characteristics of over voltage relay
APPARATUS: Over voltage relay
Auxiliary supply kit (Step-down Transformer-230/24V, Bridge rectifier, filter)
Auto transformer (0-230v, 2A)
Voltmeter (0-200v)
Rheostat (110Ω, 1.8A)
THEORY:
OVERVOLTAGE PROTECTION
The function of a relay is to detect abnormal conditions in the system and to initiate through
appropriate circuit breakers the disconnection of faulty circuits so that interference with the
general supply is minimized. There are always a chance of suffering an electrical power system
from abnormal over voltages. These abnormal over voltages may be caused due to various
reason such as, sudden interruption of heavy load, lightening impulses, switching impulses etc.
These over voltage stresses may damage insulation of various equipments and insulators of the
power system. Although, all the over voltage stresses are not strong enough to damage insulation
of system, but still these over voltages also to be avoided to ensure the smooth operation of
electrical power system. These all types of destructive and non destructive abnormal over
voltages are eliminated from the system by means of overvoltage protection. For generator
protection an overvoltage relay is used to detect failure in voltage regulation. For transformers
and transmission lines, overvoltage protection is sometimes used to detect excessive voltages
Principle:
An overvoltage relay is one that operates when input voltage exceeds a predetermined(pick up)
value.over voltage relays must be instantaneous or time-delayed devices.In order to set a time
overvoltage relay,pickup voltage and time dial need to be specified and VT ration needs to be
documented.Time overvoltage relays start to time out every time input voltage exceeds the
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setpoint.overvoltage relays complete their function and close the output contact when the
duration of the overvoltage exceeds the time delay described by the time voltage curve.
Inverse time characteristics of overvoltage relay
The inverse characteristic for overvoltage V>, is defined by the
following equation:
where:
t = operating time in seconds
TMS = time multiplier setting
V = applied input voltage
Vs = relay setting voltage
NOTE: this equation is valid for V> Vs
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Circuit Diagram:
Experimental procedure:
1. Study the construction of the relay and identify the various parts.
2. Set the pick-up value of the voltage .
3. Set the Time Multiplier Setting (TMS) initially at 1.0.
4. Adjust the voltage from 1.2 to 1.8 times the pick up voltage step wise. Record the time
taken for the overvoltage condition.
5. Vary the value of the over voltage in steps and record the time taken for the operation of
the relay in each case with the help of the timer.
6. Repeat steps 4 and 5 for TMS values of 0.8,0.6,0.5,0.2
7. Repeat the above experiment with different pick up voltage values using the plug setting
bridge.
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Tabular form
Pick-up voltage = ------ volts
S.No Voltage(v) Voltage(v)
times the
plug setting
multiplier
Tp- Operating time in sec. for TMS of
1.0 0.8 0.6 0.5 0.2
1 1.2
2 1.3
3 1.4
4 1.6
5 1.8
Model graph-Characteristics of over voltage relay :
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RESULT:
Signature of the faculty
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Date: Experiment-9
CHARACTERISTICS OF UNDER VOLTAGE RELAY
AIM: To study the characteristics of under voltage relay
APPARATUS: Under voltage relay
Auxiliary supply kit (Step-down Transformer-230/24V, Bridge rectifier, filter)
Auto transformer (0-230v, 2A)
Voltmeter (0-200v)
Rheostat (110Ω, 1.8A)
THEORY:
UNDER VOLTAGE PROTECTION
The function of a relay is to detect abnormal conditions in the system and to initiate through
appropriate circuit breakers the disconnection of faulty circuits so that interference with the
general supply is minimized. There are always a chance of suffering an electrical power system
from abnormal under voltages. An undervoltage protection is used to disconnect motors at low
system voltage to prevent problems with inrush at system voltage recovery. Single-phase
versions connected phase-phase are used for asynchronous motors, whereas measuring of
positive sequence voltage is used for synchronous motors.
Principle:
An undervoltage relay is one that operates when input voltage drops below a predetermined
value(dropout value).Undervoltage relays are usually instantaneous devices.If time delays are
needed,timers,initiated on undervoltage relay,are utilized.Undervoltage relays should complete
their function every time input voltage drops below the setpoint.The dropout voltage needs to be
specified and VT ratio needs to be documented.A typical time voltage curve for undervoltage
relay is shown below.
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Characteristics of under voltage relay
The inverse characteristic for undervoltage V<, is defined by the
following equation:
where:
t = operating time in seconds
TMS = time multiplier setting
V = applied input voltage
Vs = relay setting voltage
NOTE: this equation is valid for Vs>V
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Circuit Diagram:
Experimental procedure:
1. Study the construction of the relay and identify the various parts.
2. Set the drop out value of the voltage .
3. Set the Time Multiplier Setting (TMS) initially at 1.0.
4. Adjust the voltage from 0.5 to 0.9 times the dropout voltage step wise. Record the time
taken for the under voltage condition.
5. Vary the value of the under voltage in steps and record the time taken for the operation of
the relay in each case with the help of the timer.
6. Repeat steps 4 and 5 for TMS values of 0.8,0.6,0.5,0.2
7. Repeat the above experiment with different dropout voltage values using the plug setting
bridge.
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Tabular form
Drop-out voltage = ----- volts
S.No Voltage(v) Voltage(v)
times the
plug setting
multiplier
Tp- Operating time in sec. for TMS of
1.0 0.8 0.6 0.5 0.2
1 0.9
2 0.8
3 0.7
4 0.6
5 0.5
Model graph- Characteristics of under voltage relay :
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RESULT:
Signature of the faculty
Power Systems Lab GRIET/EEE
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Date: Experiment-10
ZONES PROTECTION
AIM:To study the zones protection characteristics of Transformer and Motor zone of a given
network.
SOFTWARE USED: ETAP Software
THEORY:
The protected zone is that part of a power system guarded by a certain protection and usually
contains one or at the most two elements of the power system. For a non-unit scheme, the zone
lies between the current transformers and the point or points on the protected circuit beyond
which the system is unable to detect the presence of a fault which is shown in figure. For a unit
scheme, the zone lies between the two or several sets of current transformers and the point or
points which together with the relays constitute the protective system
A power system is composed of number of sections (equipments) such as transformer , motor ,
generator, bus bar and transmission line. These sections are protected by protective relaying
systems comprising of Instrument Transformers, protective relays , circuit breakers (CB’s) and
communication equipment.These are called zones of protection.The protective system are
planned in such a way that the entire power system is collectively provided by them and thus no
part of the system is left unprotected In case of fault occurring on a section, its associated
protective relays should detect the fault and issue trip signals to open their associated CB’s to
isolate the faulted section from the rest of the power system in order to avoid further damage to
the power system.When a fault occurs, the protection scheme is required to trip only those circuit
breakers whose operation is required to isolate the fault. This property of selective tripping is
also called 'discrimination' and is achieved by two general methods:
1. Time Grading
Protection systems in successive zones are arranged to operate in times that are graded
through the sequence of equipments so that upon the occurrence of a fault, although a
number of protection equipments respond, only those relevant to the faulty zone complete
the tripping function. The others make incomplete operations and then reset. The speed of
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response will often depend on the severity of the fault, and will generally be slower than for
a unit system.
2. Unit Systems
It is possible to design protection systems that respond only to fault conditions
occurring within a clearly defined zone. This type of protection system is known as
'unit protection'. Certain types of unit protection are known by specific names,
e.g. restricted earth fault and differential protection. Unit protection can be applied
throughout a power system and, since it does not involve time grading, is relatively fast
in operation. The speed of response is substantially independent of fault severity. Unit
protection usually involves comparison of quantities at the boundaries of the protected
zone as defined by the locations of the current transformers
Transformer Protection: The primary objective of the Transformer Protection is to detect
internal faults in the transformer with a high degree of sensitivity and cause subsequent de-
energisation and, at the same time be immune to faults external to the transformer i.e. through
faults. Sensitive detection and deenergisation enables the fault damage and hence necessary
repairs to be limited.
Motor Protection: The abnormalities in motor or motor faults may appear due to mainly two
reasons – 1.Conditions imposed by the external power supply network,
2.Internal faults, either in the motor or in the driven plant.
Unbalanced supply voltages, under-voltage, reversed phase sequence and loss of synchronism (in
the case of synchronous motor) come under former category. The later category includes bearing
failures, stator winding faults, motor earth faults and overload etc. The motor characteristics
must be very carefully considered in selecting the right motor protection scheme.
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PARAMETERS:
SI.NO
COMPONENT
MANUFACTURER
RATING
OTHER
PARAMETERS
TO BE
SPECIFIED
1.
Power Grid
---
500MVASc
X/R =5
2.
Buses
Bus 1
Bus 2
Bus 4
Bus 5
---
13.5kV
0.48kV
0.48kV
0.48kV
---
3.
HVCB
ABB 15.5kV
In TCC kV=13.5
4.
Current
Transformer
-----
300/5
-----
5.
Fuses
Fuse 1
Fuse 2
General Electric
General Electric
12kV
6.25Kv
--------
6.
LVCB
CB1
CB2
CB3
CB4
Synchronous
Motor
ABB
ABB
ABB
ABB
-----
5kV
3.3kV
2kV
1.01kV
350HP
In TCC kV=13.5
In TCC kV=0.48
In TCC kV=0.48
In TCC kV=0.48
7. Lumped Load ------- 135kVA -----
8. Over Current
Relay
ABB ---- 1)Choose any type
of relay in OCR
2) Add CB in Output
9. Transformer ------ 1000kVA Impedance: Typical
Z and X/R
10. In-Line Relay Allen Bradley ---- -----
11. Cable ICEA (220 in library) 100ft Impedance:
R=5.75 X=5.75
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ETAP Network Diagram:
Procedure:
Construct the above network diagram in ETAP software
Specify the ratings of each device as given in the parameter table
In star protective devices select the zone of protection and get the time current
characteristics for individual Transformer, Motor, Bus Bar zones
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Characteristics of Transformer, Motor and Bus Bar zones:
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RESULT:
Signature of the faculty
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Date: Experiment-11
SHORT CIRCUIT ANALYSIS
AIM: To perform short circuit analysis to a given network or transmission line.
SOFTWARE REQUIRED: ETAP
Theory: A short circuit analysis helps us to ensure that equipment are protected by establishing
proper interrupting rating of protective devices on power systems and is required to determine
the switch gear ratings and relay ratings.The short circuit calculations must be maintained and
periodically updated to protect the equipment.The short circuit in the system cannot always be
prevented; its effect can only be reduced by considering its consequences on the system at the
time of planning and design stage . The system components, transformers, cables, switchgears,
protection equipments etc must be designed and selected to havefault withstand capability to
match system fault current rating . The objectives of performing sort circuit study are:
To prepare basis for the selection of the interrupting equipment and also to verify adequacy of
existing interrupting equipment;
To determine the system protective device settings;
To coordinate protective devices
To determine the effects of the fault currents on various system components during the time the
fault persists;
Conceptualization, design and refinement of system layout, neutral grounding, and substation
grounding;
To ascertain the minimum short-circuit current.
Short Circuit analysis is required to ensure that existing and new equipment ratings are adequate
to withstand the available short circuit energy available at each point in the electrical system. A
Short Circuit Analysis will help to ensure that personnel and equipment are protected by
establishing proper interrupting ratings of protective devices (circuit breaker and fuses). If an
electrical fault exceeds the interrupting rating of the protective device, the consequences can be
devastating. It can be a serious threat to human life and is capable of causing injury, extensive
equipment damage, and costly downtime. On large systems, short circuit analysis is required to
determine both the switchgear ratings and the relay settings. No substation equipment can be
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installed without knowledge of the complete short circuit values for the entire power distribution
system. The short circuit calculations must be maintained and periodically updated to protect the
equipment and the lives. It is not safe to assume that new equipment is properly rated.
Benefits of a Short Circuit Analysis
Performing a Short Circuit Study provides the following benefits:
Reduces the risk a facility could face and help avoid catastrophic losses.
Increases the safety and reliability of the power system and related equipment.
Evaluates the application of protective devices and equipment.
Identifies problem areas in the system.
Identifies recommended solutions to existing problems.
PARAMETERS:
SI.NO
COMPONENT
MANUFRACTURER
RATING
OTHER
PARAMETERS TO
BE SPECIFIED
1.
Power Grid
---
200MVASc
X/R=5
2.
Buses
Bus 1
Bus 2
Bus 3
---
12.47kV
12.47kV
0.48kV
-------
3.
HVCB
ABB
12kV
In TCC kV =12.47
4.
Transformer
-----
100MVA
Choose typical Z &
X/R
5.
Fuse
General Electric
6.25kV
-----
6.
LVCB
ABB
1.01kV
In TCC kV=0.48
7.
Synchronous
Motor
----- 1HP -----
8. Cable ICEA(220 in library) 100ft Impedance:
R=5.75 X=5.75
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Circuit Diagram:
Procedure:
Construct the above circuit diagram in ETAP software.
Specify the ratings of the parameters as given in the table.
Perform the short circuit analysis for a given network by inserting fault at desired
location.
Get the fault current values after simulation
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Simulation Results-
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RESULT:
Signature of the faculty
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Date: Experiment-12
TRIPPING SEQUENCE OF PROTECTIVE DEVICES
AIM: To perform Tripping sequence of protective device for given network.
SOFTWARE USED:ETAP Software
THEORY:
Star Sequence-of-Operation evaluates, verifies, and confirms the operation and selectivity of the
protective devices for various types of faults for any location directly from the one-line diagram
and via normalized Time Current Characteristic Curve views.
Sequence-of-Operation provides a system-wide solution for an accurate and realistic
operating time and state of protective devices, such as relay, fuse, circuit breaker, trip devices,
contactor, etc. The operation time is calculated for each protective device based on its settings,
time current characteristic, and interlocks for a specified fault location and type.
Sequence of Operation Key Features
User-definable fault insertion location
View device operation sequence graphically
Device failure & backup operation
Detailed relay actions (27, 49, 50, 51, 51V, 59, 67, 79, 87)
Sequence of event viewer
Current summation
Normalized (shifted) Time Current Characteristic Curves
Phase & Ground faults (symmetrical & asymmetrical)
Flashing protective device via the one-line diagram
Coordination via One-Line Diagram
Graphically place a fault anywhere on the one-line diagram
Automatically calculate & display the fault current contributions on the one-line diagram
Evaluate the operating time & state of devices based on the actual fault current
contribution flowing through each individual device
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Graphical animation of protective device operation
Globally view post fault actions & associated operating time via a tabulated event viewer
Examine the operation of protective devices via the one-line diagram.
PARAMETERS:
SI.NO
COMPONENT
MANUFACTURER
RATING
OTHER
PARAMETERS TO
BE SPECIFIED
1.
2.
3.
4.
5.
6.
7.
8.
9.
Power Grid
Buses
Bus1
Bus2
Bus3
CT1
CT2
OCR
Cable
Fuse
Transformer
CB1
CB2
Synchronous
motor
---
----
----
----
ABB
GE Multilin
735/737
(Lib-220)
ICEA
Seimens
A500-2.54KV
Lib 1HP
0.46KV(MTR)
200MVASc
12.47kV
12.47KV
12.47KV
300:5
300:5
1000KVA
Pri-12.47KV
Sec-0.48KV
POWER-
1000KVA
Siemen Allis
LA-1600A
Siemens
Static-Trip III
2HP
0.46KV
X/R=5
1.Add circuit breaker.
2.choose any type of
relay
TCC KA
Phase-12.47
1.length-100
Tolerance-0
Impedance –typical
Z&X/R ratio
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ETAP NETWORK DIAGRAM:
PROCEDURE:
Open ETAP software in the computer.
Give the file name and save it before .
Open the edit mode tab and construct the circuit. .
Give the specified ratings to the equipments given in tabular column below.
Check for errors and now click on the “ star protective devices ” icon on the top of edit mode
tab.
On the right hand side there is a toolbox click on the red fault icon and apply fault at desired
location and get the sequence of protective devices.
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Simulation Results: Sequence of Tripping observed for a given network
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RESULT:
Signature of the faculty
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Date: Experiment-13
TESTING OF NEGATIVE SEQUENCE RELAY
Aim: To study the operation of Negative sequence relay.
Apparatus: Negative sequence relay
Auxiliary supply kit (Step-down Transformer-230/24V, Bridge rectifier, filter)
Auto transformer (0-230v, 2A)
Ammeter (0-2A)
Rheostat (110Ω, 1.8A)
Theory:
Need for Negative Sequence Protection
Primary cause of motor failure is excessive heating, which if sustained over long time periods
will result in motor burn out. Overheating also reduces the life of motor. If a motor is
continuously over heated by just 10 degrees, its life can get reduced by almost 50%.
Overheating normally occurs due to over current, which in turn may be due to over loads or
locked rotor condition or low voltage or phase failure or repeat starts or phase unbalance.
Bimetallic relays are most economical solution for heating due to over loads. However they
suffer from inherent deficiencies like poor accuracy, rigid inverse time characteristics, poor
repeatability etc. They are totally insensitive to current unbalance, which is one of the major
contributors to overheating in motors.
Though the three-phase motor is supposed to be a balanced load, current unbalance occurs
frequently in motor feeders due to following:
voltage unbalance in the feeder supply
phase reversal
single phasing
Current unbalance in a motor is best represented by the presence of excessive negative sequence
component in the motor current. Consequently it is necessary to protect motors against negative
sequence.
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When the power supply to the motor is unbalanced, the unbalanced voltage and the resulting
unbalanced currents in the three phases can be resolved into three balanced components as
follows :
Positive Sequence component: This component is in the same phase sequence as that of the
motor current. All its three phases are perfectly balanced - they are equal in magnitude and are
displaced by 120 degrees. The positive sequence component represents the amount of balance in
the power supply and consequently is instrumental in delivering useful power.
Negative Sequence component: This component has a phase sequence opposite to that of the
motor current hence the name negative sequence. It represents the amount of unbalance in the
feeder. All its three phases are perfectly balanced - they are equal in magnitude and are
displaced by 120 degrees. This component does not produce useful power - however by being
present it contributes to the losses and causes temperature rise.
Zero Sequence component: This, if present, represents extent of earth fault in the feeder. All
its three phases are in the same direction.
Negative sequence relay:
The negative relays are also called phase unbalance relays because these relays
provide protection against negative sequence component of unbalanced currents existing due to
unbalanced loads or phase-phase faults. The unbalanced currents are dangerous from generators
and motors point of view as these currents can cause overheating. Negative sequence relays are
generally used to give protection to generators and motors against unbalanced currents.
A negative sequence relay has a filter circuit which is operative only for negative
sequence components. Low order of over current also can cause dangerous situations hence a
negative sequence relay has low current settings. The earth relay provides protection for phase to
earth fault but not for phase to phase fault. A negative sequence relay provides protection against
phase to phase faults which are responsible to produce negative sequence components.
Induction Type Negative Sequence Relay:
It is commonly used negative sequence relay, The schematic diagram of this type of relay
is shown in the Fig
The central limb of upper magnet carries the primary which has a Centre tap. Due to this,
the primary winding has three terminal 1, 2 and 3. The section 1-2 is energized from the
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secondary of an auxiliary transformer to R-phase. The section 2-3 is directly energized from the
Y-phase current.
The auxiliary transformer is a special device having an air gap in its magnetic circuit.
With the help of this, the phase angle between its primary and secondary can be easily adjusted.
Induction type Negative sequence relay
In practice it is adjusted such that output current lags by 120orather than usual 180ofrom
the input.
So, IR = Input current of auxiliary transformer
IR1 = Output current of auxiliary transformer
and IR1 lags IR by 120o
Hence the relay primary carries the current which is phase difference of IR1 and IR .
Positive Sequence Currents: The C.T secondary currents are shown in the Fig.(a). The Fig.(b)
shows the position of vector IR1 lagging IR by120o. The Fig..(c) shows the vector sum of IR1 and -
IY. The phase difference of IR1 and IY is the vector sum of IR1 and - IY. It can seen from the
Fig..(c) that the resultant is zero. Thus the relay primary current is zero and relay is inoperative
for positive sequence currents.
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Positive sequence currents
Negative Sequence Currents: The C.T. secondary currents are shown in the Fig..(a). The
Fig..(b) Shows the position of IR1 lagging IR by 120o. The Fig..(c) Shows the vector difference of
IR1 and IY which is the relay current.
Under negative sequence currents, the vector difference of IR1 and IY results into a current I
as shown in the Fig. This current flows through the primary coil of the relay. Under the influence
of current I, the relay operates. The disc rotates to close the trip contacts and opens the circuit
breaker.
This relay is inoperative for zero sequence currents. But the relay can be made operative for the
flow of zero sequence currents also by providing an additional winding on the central limb of the
upper magnet of the relay. This winding is connected in the residual circuit of three line C.T.
This relay is called induction type negative and zero sequence relay. The schematic arrangement
of induction type negative and zero sequence relay is shown in the Fig.
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Negative sequence currents
Induction type negative and zero sequence relay
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Block Diagram:
CTNM 12 wiring diagram
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Experimental procedure:
1. Study the construction of the relay and identify the various parts.
2. Connect the circuit for phase B for unbalanced condition.
3. Increase the current and note the value of current & time at instant of tripping.
4. Repeat the above procedure by connecting circuit for phase C and tabulate the readings.
Tabular form:
S. No
Current (A)
Tripping Time (sec)
Phase B
Phase C
RESULT:
Signature of the faculty
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