Megger- Boletín #2 sobre interruptores de potencia

7/24/2019 Megger- Boletn #2 sobre interruptores de potencia

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TSG Dover Bulletin 012Circuit Breaker II 1 of 8 17/06/2010

Application Bulletin

From: Simanand Gandhi Jeyaraj

Circui t Breakers Part II

Introduction

The importance of circuit Breaker testing and the necessity of diagnostic testing and analysing

will be understood if the important parts of a circuit breaker are known. This application note willfocus on the different important parts in a circuit breaker and its functionalities.

What are the important parts and their functionalities in a high voltage circuitbreaker?The following list provides the parts in a typical circuit breaker. This doesnt mean all of themlisted will be available in a typical high voltage circuit breaker. It depends on the design, voltagerating, indoor or outdoor, breaking capacity, manufacturers design principle etc. This also can becorrelated with the different types of circuit breakers in the market explained in Part-I applicationnote.

1) Interrupters

1.1) Main contact1.2) Arcing contact1.3) Pre-Insertion-Resistor (PIR) Contact

2) Vacuum Interrupters3) Operating Mechanism Cubic le

3.1) Trip Coil3.2) Close Coil3.3) Auxiliary Contact3.4) Spring operated mechanism3.5) Hydraulic operated mechanism3.6) Pneumatic operated mechanism

3.7) Hydraulic spring operated mechanism3.8) Magnet actuated mechanism3.9) Phase discrepancy relay / Monitor3.10) Anti pumping Relay3.11) Local / Remote Switching3.12) Spring charge motor3.13) Damping mechanism

4) SF6 Gas Monitor5) Air / Hydraulic Pressure Monitor6) Auto Reclose relay7) Synchronised Switching Relay

8) Coupling capacitors9) Grading capacitors


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TSG Dover Bulletin 012Circuit Breaker II 2 OF 8

Fig 1: Typical out door type high voltage circuit breaker

1) Interrupters / contacts Interrupters are the opening or closing contacts housed inside the gas or oil filled chamber. Itwill be housed inside the vacuum chamber for a vacuum interrupter. The functions of theseinterrupters or contacts are to carry the continuous rated current without over heating andalso to carry very large current for a short time on the occurrence of short circuit or over loadwithout deterioration. A typical interrupter will be designed in two parts as shown in the figurebelow the main contacts (Fixed and movable) and the arcing contacts (Fixed and movable).

Fig 2: Cut sectional view of an interrupter

Interrupter

OperatingMechanism

Cubicle

Arcing Contact

Main Contact


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1.1) Main contact:This is the part of the contact that carries the continuous current when thebreaker is under closed condition and will have the least contact resistance.

1.2) Arcing contact: This contact opens after the opening of main contact with a delay andtakes care of the breaking current or interrupting current. This contact is designed tohandle the arc and to withstand high temperature without pitting. The contact resistance ofthis contact will be higher than that of the Main contact resistance.

1.3) Pre-Insertion-Resistor (PIR) Contact: This contact is a special arrangement for 400KVand above rated Circuit Breakers to dampen the transient voltages and current duringswitching and also to reduce voltage dips during breaker operation.

Fig 3: PIR (Pre Insertion Resistance) contact circui t d iagram

2) VacuumInterruptersVacuum interrupters are the contact mechanism encapsulated inside a vacuum chamber orflask. This type of vacuum circuit breakers will be designed for a maximum 40KV rating(Recent developments have led upto 132KV VCB). The figure below shows some typicalvacuum interrupters and cut section view of a vacuum interrupter.

Fig 4: Vacuum Interrupter - Cut section view (Source: Siemens)

Main contact and arcing

contact

Resistor Contact


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3) Operating Mechanism Cubicle:This is where the complete operating energy is stored and controlled to operate a circuitbreaker and the following components are used in executing the breaker operatingfunction.

Fig 5: Spring operating mechanism (Source: Siemens)


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3.1) Trip Coil:Trip coil will be mounted inside the operating mechanism cubicle and is used totrigger the mechanism (spring, Pneumatic, Hydraulic or Magnetic) to trip the circuit breaker.The trip coil will be energised either manually by the operator through a switch who wantsto trip or through the protection relay on the occurrence of fault. Trip coils will be energisedthrough the substation DC, usually 110V or 220V DC systems. These coils will not be ratedfor continuous DC supply and has to be removed or cut off from the energising DC supply.The DC supply to the coils was cut off using one pair of the Auxiliary contact (52a and 52b)serially connected to coil circuit and located inside the operating mechanism.

3.2) Close Coil: Close coil is similar to trip coil construction wise, but is used to close the circuitbreaker instead of tripping.

3.3) Auxil iary Contact:This is a low voltage rated electrical switch with 10 to 20 N/O and N/Ccontacts but will be operated mechanically through the link physically connected throughthe gear mechanism from the main contact. So the position of the circuit breaker close or

open will be directly reflecting in the auxiliary contact. This switching contact signals the CBON OFF indicators and annunciators. One pair of N/C and N/O contact will be connected inseries to the trip coil and close coil as explained earlier to isolate supply to the coil afterbreaker initiation.

3.4) Spring operated mechanism: This type of operating mechanism (Ref Fig 5 and 6)willhave heavy springs to store the energy for closing and opening the breaker at very highspeed. The springs will be compressed using a motor named Spring Charge Motorlocated within the mechanism cubicle. The compressed spring will be hold in position usinga latch and will ready to operate. This latch is triggered using the operating coils (trip andclose coil).

3.5) Hydraulic operated mechanism: This mechanism does the same job as a spring

operated mechanism but the energy is stored using pressurised hydraulic fluid with anitrogen accumulator. A motor driven hydraulic pump will raise the pressure in fluid andthat pressure is used to operate the circuit breakers.

3.6) Pneumatic operated mechanism: This type of mechanism as the name suggests uses airpressure to operate the circuit breaker. The air is compressed using a compressor which isstored in an air tank will be used to operate the breakers.

3.7) Hydraulic spring operated mechanism: This type of mechanism is a hybrid type tomaking use of the advantages of both spring mechanism and hydraulic mechanism toachieve greater repeatability and temperature independent performance.

3.8) Magnetic actuator mechanism:These types of mechanisms are used for medium voltage

circuit breaker with vacuum interrupters where the energy release to operate the breaker iscompletely done with magnetic force. A magnetic actuator is energised to close or trip thecircuit breaker directly.

3.9) Phase Discrepancy relay / Monitor :This PD monitor or relay is used on circuit breakerswith separate operating mechanisms for three phases. The breaker close function will beelectrically paralleled. In case one of the pole has not closed when closing a three phasecircuit breaker, the Phase discrepancy relay which monitors the position of all three phaseswill trip the other two phases also after a delay as set on the PD relay.

3.10) Anti Pumping Relay:This relay is mounted inside the operating mechanism and will takecare of protecting the circuit breaker from multiple operations. If a closing switch of a circuitbreaker is stuck or if the close command is hold for a long time and the circuit breaker trips

with a fault trip through the relay, the breaker will close again and trip again and willcontinue until its damaged. To avoid this kind of repeated pumping action, the anti-pumping relay is used.


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3.11) Local Remote Switching:The Local / Remote selector switch is to change the switchingcontrol of the breaker from the switch yard control cubicle to the control room controlpanel or vice versa. The control room is remote for the control cubicle in yard.

3.12) Spring Charge Motor: This motor is used to charge the operating springs in a spring

operated mechanism. Once the breaker has operated the spring will be charged again andkept ready for its next operation.

3.13) Damping mechanism: The dash pot arrangement is connected to the operatingmechanism to suppress the oscillations in the contact mechanism during the close and tripoperations.

Fig 6: Typical spring Operated Mechanism (Source: ABB)

4) SF6 Gas Monitor:SF6(Sulphur hexafluoride) gas is utilised inside the interrupters to quench the arc duringthe close and open operation of the circuit breaker in SF6 type circuit breakers. Thepressure of the SF6is crucial for the arc quenching phenomenon; hence the gas pressurewill be continually monitored using an SF6gas monitor.

5) Air / Hydraulic Pressure Monitor :Similar to spring operated mechanisms, compressed air or oil will also be used to store theenergy by different manufacturers to drive the interrupters. The pneumatic pressure or thehydraulic pressure will be monitored continuously.

DASH POT


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6) Auto Reclose relay: This relay is to perform an automatic control function in a circuit breaker. Usually will work

along with a protection relay or may be built inside a protection relay. The function of thisrelay is to reclose the circuit breaker once the breaker trips on faults after a predefineddelay. The circuit breakers will hold on the close position continuously if the fault thatcaused the trip vanishes else the breaker will trip again and will not be further reclosed.

7) Synchronised Switching Relay:To control the transients in the power system caused by the randomly operated circuitbreakers during close and open, Synchronised switching mechanisms / relays wereintroduced to the breakers using resistors, capacitors, reactors, surge arrestors etc. Thesesystems will operate all the three poles of the circuit breaker exactly at the zero crossing bycreating a delay to synchronise at zero crossing of the sine wave in the power system. Thedelay will be electrical if it is a separately operated mechanism or will be mechanical if the

CB is a common operating mechanism type.

8) Coupling Capacitors: Coupling Capacitors will be connected in parallel to theinterrupters. These are used on some dead tank circuit breakers to reduce the rate of riseof breaker transient recovery voltage, and to limit the overvoltage caused by a shortdistance fault on a low capacitive line.

Fig 7: Dead tank circuit breaker with coupling capacitors

CouplingCapacitors


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9) Grading Capacitors:

Grading capacitors are connected in parallel to the interrupters on live tank circuit breakersand are used to distribute the high voltage equally.

Questions should be directed to Simanand Gandhi Jeyaraj [email protected]

Grading

Capacitor

Fig 8: Live tank circuit breaker with grading capacitors

Megger- Boletín #2 sobre interruptores de potencia

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