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NTPC LTDBGTPP
PROJECT: SWITCHYARD
SUBMITTED BY
JAYANTA KAR
RTU,KOTA
GUIDED BY
MR, ARUP BHATTACHARYA
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ACKNOLEDGEMENT
i owe a huge thanks to a large number of people without whom thispractical training of mine would not have been possible.. i express mysincere gratitude to the training and management wing of NTPCLTD, bongaigaon for giving me the opportunity to get a first handtechnical knowledge.
i am also extremely grateful to MR, ARUP BHATTACHARYA (DGMELECTRICAL) for permitting me to take training at their prestigiousorganization. i am extremely thankful for his valuable guidance andgiving me a part of his precious time.i would like to express my sincere thanks to all other for their valuableguidance and scholarly suggestions, prudent admonition, effectivemanagement which made my training process smoother....
PROJECT GUIDE SUBMITTED BY
MR A.BHATTACHARYA JAYANTA KAR
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CONTENTS
SL.NO DESCRIPTION
(A)
(B)
(C)
(i)
(ii)
(iii)
(D)
SWITCHYARD
TRANSFORMER
BASIC ASPECTS OF PROTECTION
CIRCUIT BREAKER
RELAY
ISOLATOR
CONCLUSION
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SWITCHYARD
A switchyard is essentially a hub for electrical power sources. For instance, aswitchyard will exist at a generating station to coordinate the exchange of power
between the generators and the transmission lines in the area. A switchyard willalso exist when high voltage lines need to be converted to lower voltage fordistribution to consumers.
Therefore a switchyard will contain; current carrying conductors, grounding wiresand switches, transformers, disconnects, remotely controlled arc snuffingbreakers, metering devices, etc.
SINGLE LINE DIAAGRAM OF NTPC BONGAIGAON SWITCHYARD
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Transformer
A transformeris a device that transfers electrical energy from one circuit to
another through inductively coupled conductorsthe transformer's coils. A
varying current in the first orprimarywinding creates a varying magnetic flux inthe transformer's core and thus a varying magnetic field through
the secondarywinding. This varying magnetic field induces a
varying electromotive force (EMF), or "voltage", in the secondary winding. This
effect is called mutual induction.
If a load is connected to the secondary, an electric current will flow in the
secondary winding and electrical energy will be transferred from the primary
circuit through the transformer to the load. In an ideal transformer, the induced
voltage in the secondary winding (Vs) is in proportion to the primary voltage (Vp),
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and is given by the ratio of the number of turns in the secondary ( Ns) to the
number of turns in the primary (Np) as follows:
By appropriate selection of the ratio of turns, a transformer thus allows
an alternating current (AC) voltage to be "stepped up" by making Ns greater
than Np, or "stepped down" by making Ns less than Np.
In the vast majority of transformers, the windings are coils wound around
a ferromagnetic core, air-core transformers being a notable exception.
Transformers range in size from a thumbnail-sized coupling transformer hidden
inside a stage microphone to huge units weighing hundreds of tons used to
interconnect portions ofpower grids. All operate with the same basic principles,although the range of designs is wide. While new technologies have eliminated
the need for transformers in some electronic circuits, transformers are still found
in nearly all electronic devices designed forhousehold ("mains") voltage.
Transformers are essential for high-voltage electric power transmission, which
makes long-distance transmission economically practical.
Basic principles
The transformer is based on two principles: first, that an electric current can
produce a magnetic field (electromagnetism), and, second that a changing
magnetic field within a coil of wire induces a voltage across the ends of the coil
(electromagnetic induction). Changing the current in the primary coil changes the
magnetic flux that is developed. The changing magnetic flux induces a voltage in
the secondary coil.
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An ideal transformer is shown in the adjacent figure. Current passing through the
primary coil creates a magnetic field. The primary and secondary coils are
wrapped around a core of very high magnetic permeability, such as iron, so that
most of the magnetic flux passes through both the primary and secondary coils.
Different parts of Transformer are:
1) CONSERVATOR - conservator is a type of tank , used to help oil filling this issituated upper portion of the power transformer . mainly these are cylindricallyshapped...
it is used to provide adequate space for the expansion of oil when transformer isloaded or when ambient temprature changes.
2) BREATHER - Breather is a device used for absorb the moisture content of aoil and sucked air
3)SILICA GEL BREATHER: it sucks the moisture from the air which is taken bytransformer so that dry air is taken by transformer.
4)RADIATORS: these are used for cooling of the transformer oil.
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5)BUCHHOLZ RELAY: it is avery sensitive gas and oiloperated instrument which safely detect the formation of gas or sudden prssureinside the oil transformer.
this is a protecting device used to protect our transformer windings . this is adouble ended device one end is conneced to conservator other is connected totank. there are two windings inside the relayone for detecting oil level goin to empty and other is connected to a alarm circuitfor warning
6) TANK - basically this is a container used to keep windings(both) and coolingoil.
7) PRIMARY WINDING - in the case of power transmission primary windingsare the main element external connection from the power is connected to thewinding
8) SECONDARY WINDING - this is a another windin for redusing power(in thecase of step down purpos)
Coolant
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High temperatures will damage the winding insulation. Small transformers do not
generate significant heat and are cooled by air circulation and radiation of heat.
Power transformers rated up to several hundred kVA can be adequately cooled
by natural convective air-cooling, sometimes assisted by fans. In larger
transformers, part of the design problem is removal of heat. Some power
transformers are immersed in transformer oil that both cools and insulates the
windings.The oil is a highly refined mineral oil that remains stable at
transformeroperating temperature. Indoor liquid-filled transformers are required
by building regulations in many jurisdictions to use a non-flammable liquid, or to
be located in fire-resistant rooms.Air-cooled dry transformers are preferred for
indoor applications even at capacity ratings where oil-cooled construction would
be more economical, because their cost is offset by the reduced building
construction cost.The oil-filled tank often has radiators through which the oil circulates by natural
convection; some large transformers employ forced circulation of the oil by
electric pumps, aided by external fans or water-cooled heat exchangers. Oil-filled
transformers undergo prolonged drying processes to ensure that the transformer
is completely free ofwater vaporbefore the cooling oil is introduced. This helps
prevent electrical breakdown under load. Oil-filled transformers may be equipped
withBuchholz relays, which detect gas evolved during internal arcing and rapidly
de-energize the transformer to avert catastrophic failure. Oil-filled transformers
may fail, rupture, and burn, causing power outages and losses. Installations of
oil-filled transformers usually includes fire protection measures such as walls, oil
containment, and fire-suppression sprinkler systems.
Polychlorinated biphenyls have properties that once favored their use as
a coolant, though concerns over theirenvironmental persistence led to a
widespread ban on their use. Today, non-toxic, stable silicone-based oils,
orfluorinated hydrocarbons may be used where the expense of a fire-resistant
liquid offsets additional building cost for a transformer vault. Before 1977, even
transformers that were nominally filled only with mineral oils may also have been
contaminated with polychlorinated biphenyls at 10-20 ppm. Since mineral oil and
PCB fluid mix, maintenance equipment used for both PCB and oil-filled
transformers could carry over small amounts of PCB, contaminating oil-filled
transformers.
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Some "dry" transformers (containing no liquid) are enclosed in sealed,
pressurized tanks and cooled by nitrogen orsulfur hexafluoride gas.
Experimental power transformers in the 2 MVA range have been built
with superconducting windings which eliminates the copper losses, but not the
core steel loss. These are cooled by liquid nitrogen orhelium.
TYPES
Current transformers
A current transformer (CT) is a measurement device designed to provide a
current in its secondary coil proportional to the current flowing in its primary.
Current transformers are commonly used in metering and protective relays in
the electrical power industry where they allow safe measurement of large
currents, often in the presence ofhigh voltages. The current transformer safely
isolates measurement and control circuitry from the high voltages typically
present on the circuit being measured.
Current transformers are often constructed by passing a single primary turn
(either an insulated cable or an uninsulated bus bar) through a well-
insulatedtoroidal core wrapped with many turns of wire. The CT is typically
described by its current ratio from primary to secondary. For example, a 4000:5
CT would provide an output current of 5 amperes when the primary was passing
4000 amperes. The secondary winding can be single ratio or have
severaltap points to provide a range of ratios. Care must be taken that the
secondary winding is not disconnected from its load while current flows in the
primary, as this will produce a dangerously high voltage across the open
secondary and may permanently affect the accuracy of the transformer.
Specially constructed wideband CTs are also used, usually with an oscilloscope,
to measure high frequencywaveforms or pulsed currents within pulsed
powersystems. One type provides a voltage output that is proportional to themeasured current; another, called a Rogowski coil, requires an
external integratorin order to provide a proportional output.
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Voltage transformers
Voltage transformers (VT) or potential transformers (PT) are another type of
instrument transformer, used for metering and protection in high-voltage circuits.
They are designed to present negligible load to the supply being measured and
to have a precise voltage ratio to accurately step down high voltages so that
metering and protective relay equipment can be operated at a lower potential. Typically
the secondary of a voltage transformer is rated for 69 V or 120 V at rated primary
voltage, to match the input ratings of protective relays.
The transformer winding high-voltage connection points are typically labeled as
H1, H2 (sometimes H0 if it is internally grounded) and X1, X2 and sometimes an
X3 tap may be present. Sometimes a second isolated winding (Y1, Y2, Y3) may
also be available on the same voltage transformer. The high side (primary) may
be connected phase to ground or phase to phase. The low side (secondary) is
usually phase to ground.
The terminal identifications (H1, X1, Y1, etc.) are often referred to as polarity. This
applies to current transformers as well. At any instant terminals with the same
suffix numeral have the same polarity and phase. Correct identification of
terminals and wiring is essential for proper operation of metering and protective
relays.
Some meters operate directly on the secondary service voltages at or below 600
V. VTs are typically used for higher voltages (for example, 765 kV for power
transmission) , or where isolation is desired between the meter and the
measured circuit.
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ISOLATOR
A device or assembly of devices which isolates or disconnects an on-hookstation or CTS from all wires which exit the PCZ and which has been acceptedas effective for security purposes by the Telephone Security Panel.
An isolator is not the same as a switch. It should only be opened when notcarrying current, and has the purpose of ensuring that a circuit cannot becomelive whilst it is out of service for maintenance or cleaning. The isolator must breakall live supply conductors; thus both phase and neutral conductors must beisolated. It must, however, be remembered that switching off for mechanical
maintenance is likely to be carried out by non-electrically skilled persons andthat they may therefore unwisely use isolators as on-load switches. To preventan isolator, which is part of a circuit where a circuit breaker is used for switching,from being used to break load current, it must be interlocked to ensure operationonly after the circuit breaker is already open. In many cases an isolator can beused to make safe a particular piece of apparatus whilst those around it are stilloperating normally.
HORIZONTAL DOUBLE BREAK ISOLATOR
This type of construction has three insulator stacks per pole. The two one eachside is fixed and one at the center is rotating type. The central insulator stack canswing about its vertical axis through about 900C. The fixed contacts are providedon the top of each of the insulator stacks on the side. The contact bar is fixedhorizontally on the central insulator stack. In closed position, the contact shaftconnects the two fixed contacts. While opening, the central stack rotates through900C, and the contact shaft swings horizontally giving a double break.
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The isolators are mounted on a galvanized rolled steel frame. The three polesare interlocked by means of steel shaft. A common operating mechanism isprovided for all the three poles. One pole of a triple pole isolator is closed
position.
PANTOGRAPH ISOLATOR
Illustrates the construction of a typical pantograph isolator. While closing, thelinkages of pantograph are brought nearer by rotating the insulator column. Inclosed position the upper two arms of the pantograph close on the overheadstation bus bar giving a grip. The current is carried by the upper bus bar to thelower bus bar through the conducting arms of the pantograph. While opening, therotating insulator column is rotated about its axis. Thereby the pantograph bladescollapse in vertical plane and vertical isolation is obtained between the lineterminal and pantograph upper terminal.
Pantograph isolators cover less floor area. Each pole can be located at a suitablepoint and the three poles need not be in one line, can be located in a line atdesired angle with the bus axis.
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OPERATION
It is a device meant for load operation hence not to operate while it carries loadcurrent. It cannot be operated with less pressure i.e. hesitatingly with small jugsi.e. to operate firmly in one stroke only. Also put on hand gloves while operatingthe switch. The operation of three poles is obtained by mechanical interlocking ofthe three poles. Further for all three poles there is a common operatingmechanism.
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Circuit breaker
A circuit breakeris an automatically operated electricalswitch designed to
protect an electrical circuit from damage caused by overload orshort circuit. Its
basic function is to detect a fault condition and, by interrupting continuity, to
immediately discontinue electrical flow. Unlike a fuse, which operates once and
then has to be replaced, a circuit breaker can be reset (either manually or
automatically) to resume normal operation. Circuit breakers are made in varying
sizes, from small devices that protect an individual household appliance up to
large switchgeardesigned to protect high voltage circuits feeding an entire city.
Operation
All circuit breakers have common features in their operation, although details
vary substantially depending on the voltage class, current rating and type of the
circuit breaker.
The circuit breaker must detect a fault condition; in low-voltage circuit breakers
this is usually done within the breaker enclosure. Circuit breakers for large
currents or high voltages are usually arranged with pilot devices to sense a fault
current and to operate the trip opening mechanism. The trip solenoid that
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releases the latch is usually energized by a separate battery, although some
high-voltage circuit breakers are self-contained with current
transformers,protection relays, and an internal control power source.
Once a fault is detected, contacts within the circuit breaker must open to interrupt
the circuit; some mechanically-stored energy (using something such as springs
or compressed air) contained within the breaker is used to separate the contacts,
although some of the energy required may be obtained from the fault current
itself. Small circuit breakers may be manually operated; larger units
have solenoids to trip the mechanism, and electric motors to restore energy to
the springs.
The circuit breaker contacts must carry the load current without excessive
heating, and must also withstand the heat of the arc produced when interrupting
the circuit. Contacts are made of copper or copper alloys, silver alloys, and other
materials. Service life of the contacts is limited by the erosion due to interrupting
the arc. Miniature and molded case circuit breakers are usually discarded when
the contacts are worn, but power circuit breakers and high-voltage circuit
breakers have replaceable contacts.
When a current is being interrupted, an arc is generated. This arc must be
contained, cooled, and extinguished in a controlled way, so that the gap between
the contacts can again withstand the voltage in the circuit. Different circuit
breakers use vacuum, air, insulating gas, oroil as the medium in which the arc
forms. Different techniques are used to extinguish the arc including:
Lengthening / deflection of the arc
Intensive cooling (in jet chambers)
Division into partial arcs
Zero point quenching (Contacts open at the zero current time crossing of
the AC waveform, effectively breaking no load current at the time of opening.
The zero crossing occurs at twice the line frequency i.e. 100 times per secondfor 50Hz and 120 times per second for 60Hz AC)
Connecting capacitors in parallel with contacts in DC circuits
Finally, once the fault condition has been cleared, the contacts must again be
closed to restore power to the interrupted circuit.
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Types of circuit breaker
Low voltage circuit breakers
Low voltage (less than 1000 VAC) types are common in domestic, commercial and
industrial application, and include:
MCB (Miniature Circuit Breaker)rated current not more than 100 A. Trip
characteristics normally not adjustable. Thermal or thermal-magnetic
operation. Breakers illustrated above are in this category.
MCCB (Molded Case Circuit Breaker)rated current up to 2500 A.
Thermal or thermal-magnetic operation. Trip current may be adjustable in
larger ratings.
Low voltage power circuit breakers can be mounted in multi-tiers in low-
voltage switchboards orswitchgearcabinets.
The characteristics of Low Voltage circuit breakers are given by international
standards such as IEC 947. These circuit breakers are often installed in draw-out
enclosures that allow removal and interchange without dismantling the
switchgear.
Large low-voltage molded case and power circuit breakers may have electrical
motor operators, allowing them to be tripped (opened) and closed under remote
control. These may form part of an automatic transfer switch system for standby
power.
Low-voltage circuit breakers are also made for direct-current (DC) applications,
for example DC supplied for subway lines. Special breakers are required for
direct current because the arc does not have a natural tendency to go out on
each half cycle as for alternating current. A direct current circuit breaker will haveblow-out coils which generate a magnetic field that rapidly stretches the arc when
interrupting direct current.
Small circuit breakers are either installed directly in equipment, or are arranged in
a breaker panel.
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The 10 ampere DIN rail-mounted thermal-magnetic miniature circuit breaker is
the most common style in modern domestic consumer units and commercial
electrical distribution boards throughout Europe. The design includes the
following components:
1. Actuatorlever- used to manually trip and reset the circuit breaker.
Also indicates the status of the circuit breaker (On or Off/tripped). Most
breakers are designed so they can still trip even if the lever is held or
locked in the "on" position. This is sometimes referred to as "free trip" or
"positive trip" operation.
2. Actuator mechanism - forces the contacts together or apart.3. Contacts - Allow current when touching and break the current when
moved apart.
4. Terminals
5. Bimetallic strip.
6. Calibration screw - allows the manufacturerto precisely adjust the
trip current of the device after assembly.
7. Solenoid
8. Arc divider/extinguisher
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Magnetic circuit breaker
Magnetic circuit breakers use a solenoid (electromagnet) whose pulling force
increases with the current. Certain designs utilize electromagnetic forces in
addition to those of the solenoid. The circuit breaker contacts are held closed by
a latch. As the current in the solenoid increases beyond the rating of the circuit
breaker, the solenoid's pull releases the latch which then allows the contacts to
open by spring action. Some types of magnetic breakers incorporate a hydraulic
time delay feature using a viscous fluid. The core is restrained by a spring until
the current exceeds the breaker rating. During an overload, the speed of the
solenoid motion is restricted by the fluid. The delay permits brief current surges
beyond normal running current for motor starting, energizing equipment, etc.
Short circuit currents provide sufficient solenoid force to release the latch
regardless of core position thus bypassing the delay feature. Ambient
temperature affects the time delay but does not affect the current rating of a
magnetic breaker
Thermal magnetic circuit breaker
Thermal magnetic circuit breakers, which are the type found in most distribution
boards, incorporate both techniques with the electromagnet responding
instantaneously to large surges in current (short circuits) and the bimetallic strip
responding to less extreme but longer-term over-current conditions. The thermal
portion of the circuit breaker provides an "inverse time" response feature which
provides faster or slower response for larger or smaller over currents
respectively.
http://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Current_(electricity)http://en.wikipedia.org/wiki/Distribution_boardhttp://en.wikipedia.org/wiki/Distribution_boardhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Current_(electricity)http://en.wikipedia.org/wiki/Distribution_boardhttp://en.wikipedia.org/wiki/Distribution_board8/4/2019 Trainning Report of Ntpc,Bongaigaon
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Common trip breakers
When supplying a branch circuit with more than one live conductor, each live
conductor must be protected by a breaker pole. To ensure that all live conductors
are interrupted when any pole trips, a "common trip" breaker must be used.
These may either contain two or three tripping mechanisms within one case, or
for small breakers, may externally tie the poles together via their operating
handles. Two pole common trip breakers are common on 120/240 volt systems
where 240 volt loads (including major appliances or further distribution boards)
span the two live wires. Three-pole common trip breakers are typically used to
supply three-phase electric powerto large motors or further distribution boards.
Two and four pole breakers are used when there is a need to disconnect the
neutral wire, to be sure that no current can flow back through the neutral wire
from other loads connected to the same network when people need to touch the
wires for maintenance. Separate circuit breakers must never be used for
disconnecting live and neutral, because if the neutral gets disconnected while the
live conductor stays connected, a dangerous condition arises: the circuit will
appear de-energized (appliances will not work), but wires will stay live
and RCDs will not trip if someone touches the live wire (because RCDs needpower to trip). This is why only common trip breakers must be used when
switching of the neutral wire is needed
http://en.wikipedia.org/wiki/Major_appliancehttp://en.wikipedia.org/wiki/Three-phase_electric_powerhttp://en.wikipedia.org/wiki/Residual-current_devicehttp://en.wikipedia.org/wiki/File:Breaker3phase2a_proc.jpghttp://en.wikipedia.org/wiki/Major_appliancehttp://en.wikipedia.org/wiki/Three-phase_electric_powerhttp://en.wikipedia.org/wiki/Residual-current_device8/4/2019 Trainning Report of Ntpc,Bongaigaon
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Medium-voltage circuit breakers
Medium-voltage circuit breakers rated between 1 and 72 kV may be assembledinto metal-enclosed switchgear line ups for indoor use, or may be individual
components installed outdoors in a substation. Air-break circuit breakers
replaced oil-filled units for indoor applications, but are now themselves being
replaced by vacuum circuit breakers (up to about 35 kV). Like the high voltage
circuit breakers described below, these are also operated by current sensing
protective relays operated through current transformers. The characteristics of
MV breakers are given by international standards such as IEC 62271. Medium-
voltage circuit breakers nearly always use separate current sensors
and protective relays, instead of relying on built-in thermal or magnetic
overcurrent sensors.
Medium-voltage circuit breakers can be classified by the medium used to
extinguish the arc:
Vacuum circuit breakerWith rated current up to 3000 A, these breakers
interrupt the current by creating and extinguishing the arc in a vacuum
container. These are generally applied for voltages up to about 35,000
V, which corresponds roughly to the medium-voltage range of power systems.Vacuum circuit breakers tend to have longer life expectancies between
overhaul than do air circuit breakers.
Air circuit breakerRated current up to 10,000 A. Trip characteristics are
often fully adjustable including configurable trip thresholds and delays.
Usually electronically controlled, though some models
are microprocessorcontrolled via an integral electronic trip unit. Often used
for main power distribution in large industrial plant, where the breakers are
arranged in draw-out enclosures for ease of maintenance.
SF6 circuit breakers extinguish the arc in a chamber filled with sulfur
hexafluoride gas.
http://en.wikipedia.org/wiki/Electrical_substationhttp://en.wikipedia.org/wiki/Relayhttp://en.wikipedia.org/wiki/Current_transformerhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Microprocessorhttp://en.wikipedia.org/wiki/Electrical_substationhttp://en.wikipedia.org/wiki/Relayhttp://en.wikipedia.org/wiki/Current_transformerhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Microprocessor8/4/2019 Trainning Report of Ntpc,Bongaigaon
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High-voltage circuit breakers
Electrical power transmission networks are protected and controlled by high-
voltage breakers. The definition ofhigh voltage varies but in power transmission
work is usually thought to be 72.5 kV or higher, according to a recent definition
by the International Electrotechnical Commission (IEC). High-voltage breakers
are nearly alwayssolenoid-operated, with current sensing protective
relays operated through current transformers. In substations the protective relay
scheme can be complex, protecting equipment and buses from various types of
overload or ground/earth fault.
High-voltage breakers are broadly classified by the medium used to extinguish
the arc.
Bulk oil
Minimum oil
Air blast
Vacuum
SF6
Due to environmental and cost concerns over insulating oil spills, most newbreakers use SF6 gas to quench the arc.
Circuit breakers can be classified as live tank, where the enclosure that contains
the breaking mechanism is at line potential, ordead tankwith the enclosure at
earth potential. High-voltage AC circuit breakers are routinely available with
ratings up to 765 kV. 1200KV breakers are likely to come into market very soon
High-voltage circuit breakers used on transmission systems may be arranged to
allow a single pole of a three-phase line to trip, instead of tripping all three poles;
for some classes of faults this improves the system stability and availability.
http://en.wikipedia.org/wiki/Power_transmissionhttp://en.wikipedia.org/wiki/International_Electrotechnical_Commissionhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Current_transformerhttp://en.wikipedia.org/wiki/Electrical_substationhttp://en.wikipedia.org/wiki/Sulfur_hexafluoridehttp://en.wikipedia.org/wiki/Sulfur_hexafluoridehttp://en.wikipedia.org/wiki/Power_transmissionhttp://en.wikipedia.org/wiki/International_Electrotechnical_Commissionhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Current_transformerhttp://en.wikipedia.org/wiki/Electrical_substationhttp://en.wikipedia.org/wiki/Sulfur_hexafluoride8/4/2019 Trainning Report of Ntpc,Bongaigaon
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Relay
A relay is an electrically operated switch. Many relays use an electromagnet to
operate a switching mechanism mechanically, but other operating principles are
also used. 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. The first
relays were used in long distance telegraph circuits, repeating the signal coming
in from one circuit and re-transmitting it to another. Relays were used extensively
in telephone exchanges and early computers to perform logical operations.
A type of relay that can handle the high power required to directly control an
electric motor is called a contactor. Solid-state relays control power circuits with
nomoving parts, instead using a semiconductor device to perform switching.
Relays with calibrated operating characteristics and sometimes multiple
operating coils are used to protect electrical circuits from overload or faults; in
modern electric power systems these functions are performed by digital
instruments still called "protective relays".
Applications
Relays are used to and for:
Control a high-voltage circuit with a low-voltage signal, as in some types
ofmodems or audio amplifiers,
Control a high-current circuit with a low-current signal, as inthe startersolenoid of an automobile,
Detect and isolate faults on transmission and distribution lines by opening
and closing circuit breakers (protection relays),
http://en.wikipedia.org/wiki/Electrichttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Contactorhttp://en.wikipedia.org/wiki/Solid-state_relayshttp://en.wikipedia.org/wiki/Moving_partshttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Modemshttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Starter_motorhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Circuit_breakershttp://en.wikipedia.org/wiki/Electrichttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Contactorhttp://en.wikipedia.org/wiki/Solid-state_relayshttp://en.wikipedia.org/wiki/Moving_partshttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Modemshttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Starter_motorhttp://en.wikipedia.org/wiki/Solenoidhttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Circuit_breakers8/4/2019 Trainning Report of Ntpc,Bongaigaon
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Conclusion:
I am very glad after completing my vocational training as now I am
familiar with many electrical systems specially the switchyard and its parts
about which I had been unknown in the institute. During the vocational
training I had been exposed to the practical electrical equipments which are
totally different from those we are familiar with in the institute. I had been
made familiar with cooling system and many working system of transformer
which play very important role in AC systems.
In making the vocational training a successful one my guide DGM Mr. A.
Bhattachrya had always been helpful in all related matters.all staffs of
Electrical Erection Department had been so nice and helpful to me
regarding technical matters during the vocational training.