HT LT SWGR
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Transcript of HT LT SWGR
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HT LT SWGR
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SWITCH A switch is simply a means of
opening or closing the current path
in an electric circuit. There is no special opening
condition for short circuit or other
fault. It is operated manually.
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FUSE A fuse is used for over current
and short circuit protection.
Fuse has the major drawback ofreplacement after every use.
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CIRCUIT BREAKERThe circuit breaker is a piece of
equipment which can do any one of thefollowing tasks:
Makes or breaks a circuit either
manually or by remote control undernormal conditions
Breaks a circuit automatically under
fault conditions
Makes a circuit either manually or byremote control under fault conditions
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CIRCUIT BREAKER
A circuit breaker is a switching i.e.
current interrupting or makingdevice in switchgear.
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SWITCHGEAR
It is the generic term including the
entire range of switching devices andtheir combination with associated
control, measuring, protecting, and
regulating equipment.
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FUNCTIONS OF SWITCHGEAR Carrying the normal load current
Making or breaking the normal load
current Clearing the fault current (for which
sensing devices like CT, PT, and
various relays are employed)
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COMPONENTS OF SWITCHGEAR Circuit Breaker
Current Transformer (CT)
Potential Transformer (PT)
Protective Relays
Measuring Instruments
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COMPONENTS OF SWITCHGEAR Switches
Fuses
Surge Arresters
Isolators
Miniature Circuit Breakers (MCB)
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SWITCHGEAR REQUIREMENTSThere are several voltage levels andfault situations between the generatingstations to the final load points. Henceswitchgear requirements may varydepending upon following factors:
Location
Ratings Local Needs
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LOW VOLTAGE SWITCHGEARS
Switchgears for low voltage
applications are rated up t01500 V.
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LV Switchgears
Oil Circuit Breakers (OCB)
Air-Circuit Breakers (ACB)
Switch-Fuse Units (SFU)
Off-Load Isolators
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LV Switchgears HRC Fuses
Earth Leakage Circuit
Breakers(ELCB) Miniature Circuit Breakers (MCB)
Moulded Case Circuit Breakers
(MCCB)
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MEDIUM VOLTAGE SWITCHGEARS
Switchgears for medium
voltage applications are rated inbetween 3.3 kV to 33 kV.
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MEDIUM VOLTAGE SWITCHGEARS
This type of switchgears is mainly
used for the distribution of electrical
energy, connected to variouselectrical networks.
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HIGH VOLTAGE SWITCHGEARS
The high voltage switchgears
range from 66 kV to 800 kV.
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SWITCHGEARS CONSIDERATIONS
While using switchgears in a power
system certain considerations mustbe kept in mind.
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SWITCHGEARS CONSIDERATIONS
1.Location of the equipment
Indoor Outdoor
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2. System Parameters
System Earthing
Frequency Insulation Level
Ambient Conditions
Ratings (both normal and shortcircuit ratings)
SWITCHGEARS
CONSIDERATIONS
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ERECTION OF SWITCHGEARSIt includes:
Placing the equipment on foundation
Assembly of loose supplied parts
Mechanical and electricalinterconnections
Connections of control and powercircuits
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SWITCHGEAR COMMISSIONING Commissioning is done to carry out pre-
defined checks and tests.
Testing is necessary to ensure that the
installation work meets the specifiedrequirements and safety norms.
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Switchgear classification
By the current rating.
By interrupting rating (maximum short circuit current that the device can safelyinterrupt) Circuit breakers can open and close on fault currents Load-break/Load-make switches can switch normal system load currents Isolators may only be operated while the circuit is dead, or the load current is very
small.
By voltage class:
Low voltage (less than 1,000 volts AC) Medium voltage (1,00033,000 volts AC) High voltage (more than 66,000 volts AC)
By insulating medium: Air Gas (SF6 or mixtures) Oil Vacuum
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Switchgear classification
By construction type: Indoor (further classified by IP (Ingress Protection) class or NEMA enclosure
type) Outdoor Industrial Utility Marine Draw-out elements (removable without many tools) Fixed elements (bolted fasteners) Live-front Dead-front Open Metal-enclosed
Metal-clad Metal enclose & Metal clad Arc-resistant
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Switchgear classification
By operating method: Manually-operated
Motor-operated
Solenoid/stored energy operated
By type of current: Alternating current
Direct current
By application:
Transmission system Distribution.
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Main functions of switchgear
Electrical protection
Electrical isolation of sections of an
installation Local or remote switching
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Electricalprotection against
Isolation Control
Overload currents
Short-circuitcurrents
Insulation failure
Isolation clearly
indicated by anauthorized fail-proof mechanicalindicator
A gap orinterposedinsulating barrierbetween theopen contacts,
clearly visible
Functional
switchingEmergencyswitching
Emergency
stoppingSwitching off formechanicalmaintenance
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Electrical protection The protection of circuits
Against overload;
Against short-circuit currents
The protection of persons Against insulation failures.
The protection of electric motors
Against overheating
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Isolation To separate a circuit or apparatus from the
remainder of a system which is energized. An isolating device must fulfil the following
requirements:
All poles of a circuit, including the neutral must be provided with a locking system inopen position
must comply with a recognized national or
international standard
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Isolation To separate a circuit or apparatus from the
remainder of a system which is energized. An isolating device must fulfil the following
requirements:
All poles of a circuit, including the neutral must be provided with a locking system inopen position
must comply with a recognized national or
international standard
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Switchgear controlFunctional control
This control relates to all switchingoperations in normal service conditions forenergizing or de-energizing a part of a
system or installation, or an individualpiece of equipment, item of plant etc.
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Switchgear controlEmergency switching
An emergency switching is intended to de-energize a live circuit which is, or couldbecome, dangerous (electric shock or fire).
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Switchgear controlMaintenance operations on the power
system
This operation assures the stopping of a
machine and its impossibility to beinadvertently restarted while mechanicalmaintenance work is being carried out on
the driven machinery.
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Supply fromsource
Equipment
RELAY
BatteryTrip Coil
ofBreaker
CB
CT
Basic relay circuit scheme
Main Parts of a Circuit Breaker :
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Main Parts of a Circuit Breaker :
* Fixed Contact
* Movable Contact
* Operating Mechanism
* Arc extinguishing medium
Fault clearing process :
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Fault clearing process :
During any Fault..
* Fault impedance will be low, so fault current willincrease and relay senses this increase in current.
* Relay contacts closes and sends trip signal to circuit
breaker and the trip coil of the circuit breaker will get
energized.* Operating mechanism of the circuit breaker will
operate and separate the contacts.
* Arc will be initiated between the contacts and it is
extinguished by suitable methods.
Arcing phenomenon :
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Arcing phenomenon :
- When a fault occurs, heavy current flows through the contacts
of the circuit breaker before they are opened by the protective system.
- At the instant when the contacts begin to separate, the contact
area decreases rapidly and current density (I/A) increases and hence
rise in temperature.
-The heat produced is sufficient to ionise the medium between thecontacts. This ionised medium acts as conductor and an arc is struck
between the contacts.
- The potential difference between the contacts is very small and
is sufficient to maintain the arc.
- The current flow depends upon the Arc resistance.
Few definitions :
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Few definitions :
Breaking Capacity Max fault current at which a CB is capable
of breaking a circuit.
Making Capacity Max current a CB can withstand if it closing on
existing Short circuit.
Restriking Voltage After the arc has been extinguished, the
voltage across the breaker terminals does not normalize
instantaneously but it oscillates The transient voltage which appears
across the breaker contacts at the instant of arc being extinguished.
Recovery Voltage Power frequency voltage which appears acrossthe breaker contacts after the arc is finally extinguished and transient
oscillations die out.
Events/Timings during fault clearing process :
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Events/Timings during fault clearing process :
Fault clearingTime
Relay time Circuit breakerTime
InstantOf
Fault
Closure ofTrip
Circuit
Final arc
ExtinctionCircuit breaker
Time
Closure ofTrip
Circuit
= +
=
= to
toRelay time
Various types of CBs :
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Various types of CBs :
(i) Miniature CB
(ii) Air Break CB
(iii) Air Blast CB
(iv) Oil CB
(v) SF6 CB
(vi) Vacuum CB
Bulk Oil CB
Minimum Oil CB
Air Break CB :
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Air Break CB :
Air Blast CB :
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Air Blast CB :
ABCB Principle of arc quenching
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ABCB- Principle of arc quenching
Bulk Oil CB :
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Bulk Oil CB :
Minimum Oil CB :
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Minimum Oil CB :
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SF6 CB :
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SF6 CB :
1. Op mechanism
2. Interrupter
3. Support
4. Op rod5. Linkage
6. Terminals
7. Filters
8. Puffer cylinder
9. Nozzle
10. Fixed position
11. Fixed contact
12. Moving contact
13. Gas inlet
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400kV Circuit Breaker
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Advantage of SF6
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* Inert gas with high dielectric strength.
* Colour less and odour less.* Non-toxic and non- inflammable.
* Sf6 is blown axially to the arc, hence it removes the heat
by axial convection and radial dissipation. As result the
arc dia reduces and comes to zero at current zero.
* Gas pressure in the chamber is at 5 ksc.
* SF6 is filled at a pressure of 12 ksc in the tank and
maintained by means of an individual or a commoncompressor.
* The decomposition products of arcing are not explosive
hence no chance of fire.
Advantage of SF6
Vacuum CB :
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Advantage of vacuum CB
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* Used up to 66 KV.
* Vacuum is of the range of 106 to 108 torr.
* Vacuum is highly dielectric, so arc cant persists.
* Separation of contacts causes the release of metal vapour fromthe contacts, the density of vapour depends on the fault current.
* At current zero the vapour emission will tends to zero and thedensity will becomes zero and dielectric strength will build up andrestriking will be prevented.
* No emission to atmosphere, hence pollution free.
* Non- explosive and silent operation.* Compact size.
Advantage of vacuum CB
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Disadvantages
* High initial cost.
* Surge suppressors (R or RC combination) are to be connected
at load side for limiting switching over-voltage while
switching low pf loads.
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MOVING PORTION
(Mechanism cover
removed)
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MECHANISM AND ITS OPERATION :
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GEAR BOX
MOTOR
CLOSINGSPRING
CLOSINGCOIL
TRIPPINGCOIL
MECHANISMSHAFT
LIMITSWITCH
TRIPPINGSPRING
SAFETY INTERLOCKS:
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The various interlocks provided on the breakerensure that-
(A) VCB Truck cannot be racked in inside the panelunless:
i) Door is closed .ii) Breaker is in tripped condition.iii) Plug & socket are engaged properly.
(B) VCB Truck can not be racked out from panelunless:
i) Door is closed.ii) Breaker is tripped .
Door cannot be opened unless the breaker is intripped condition .
Breaker can be closed only in SERVICE or in TEST position.
AUTO RECLOSURE
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AUTO RECLOSURE
Over 80% of the faults are transient in
nature. Designed to carry out one or two fast closing
operations followed by automatically locked
open.
AUTO RECLOSURE
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AUTO RECLOSURE
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FEATURES OF ISOLATORS OPERATES UNDER NO LOAD CONDITION
INTERLOCKED WITH BREAKERS ANDEARTHSWITCHES
MOTOR DRIVEN AND HAND DRIVEN
LOCAL AS WELL AS REMOTE OPERATIONPOSSIBLE
ISOLATES SECTIONS FOR MAINTENANCE USED TO SELECT BUS BARS
SELECT CT FOR BUS BAR PROTECTION
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400kV Isolator
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Isolator
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FEATURES OF EARTH SWITCHES USED TO GROUND SECTIONS REQUIRED FOR
MAINTENANCE
GROUND INDUCTION VOLTAGES
INTERLOCKED WITH BREAKERS AND ISOLATORS
CAN OPERATE FROM LOCAL ONLY
MOTOR DRIVEN AS WELL AS HAND DRIVEN SAFETY DEVICE
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CB
Earth S/W
IsolatorIsolator Load
Source
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Lightning Arrestors
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Purpose :
- To discharge the high voltage surges in the power
system due to lightning to the ground.
Apparatus to be protected :
* Overhead linesEarth/Ground wires
* HV equipmentLAs
* Substation...Lightning Masts, Earth wires
Types :
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Rod gap LA :
Insulator
Equipment
body
Rod gap
* Gap length is such that
the break-down occurs at
80% of the spark voltage
* After the surge, the arc
in the gap is maintained
by the normal supply
voltage.
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400kV Surge Arrester
Metal Oxide surge arrestor
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g
The gapless arresters are
based on metal oxide (MO)resistors, which have anextremely non-linear V/I
characteristic and a highenergy-absorptioncapability.
They are known as metal
oxide surge arresters, MOarresters for short.
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THANK
YOU