EHV CIRCUIT BREAKERS

ABOUT SWITCHGEAR

1. EHV breaker manufacturing operations Started in 1969.

2. Pioneer in high voltage breaker in the country with more than 15,000 (including MOCBs) breakers in the grid with more than four decades of experience.

3. About 35% ( more than 700 nos.) population of 400kV breaker in Indian grid.

4. Complete range of manufacturing and test facilities for breakers upto 800kV.

Product range

• SF6 gas circuit breaker

– Type 3AT4/5 550kV to 800kV

– Type 3AT2/3 420kV

– Type 3AV1 245kV

– Type 3AR1EG 145kV

• A circuit breaker is defined as a mechanical device capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying for a specific time and breaking currents under specific abnormal circuit conditions such as those of short circuit.

• The main functions of HV circuit-breakers can be categorized into four functions:

� Switching-off operating currents

� Switching-on operating currents

� Short-circuit current interruption

� Secure open and closed position

• Physical requirements of EHV CB: � Behave as a good conductor during a

closed position.

Good isolator during an open position.

� Do not generate overvoltage's during

switching.

� Keep high reliability during operation

CLASIFICATION OF CIRCUIT BREAKERS

Based on VoltageLow -less than 1kVMedium - 1kV to 52kVHigh/Extra High- 66kV to 765kVUltra High -above 765kV

Based on locationIndoor Outdoor

� Based on External designdead tank Live tank

Based on Interrupting mediaAir breakAir blastBulk oilMinimum oilSF6 gas insulatedvacuum

• Important standards• IEC• 62271-1General and definitions• 62271-100 Classification, Design and construction, Type and routine testing, Selection of

circuit breakers for service, Information in enquiries, tenders and orders.

• ANSI(American National Standards Institute)• C3704–1979 Rating structure• C3706–1979 Preferred ratings• C3709–1979 Test procedure• C3710–1979 Application guide• C3711–1979 Application guide for transient recovery voltage• C3712–1979 Capacitance current switching

MAIN COMPONENTES 42OKV EHV CB

INTERRUPTER UNIT

INSULATOR COLUMN

CONTROL UNIT

DRIVE UNIT

BELL CRANK HOUSING

• Components of HV circuit-breakers

regarding basic functions can be divided into

five groups:

a). Insulation:

Electric insulation of HV CB is

Gaseous, liquid and solid

dielectric materials. Ex.

Interrupter.

b). Current carrying:

The current carrying parts are significant

components that assure the flowing of

current in the closed position.

The failure of these parts can lead to

catastrophic events.

Ex. Guide tube.

c). Switching:

HV circuit-breakers subjected to

electrical, thermal and mechanical stresses.

It is required that they should be able to

make and break large amount of power

without causing failures.

 d). Operating mechanism:

The operating mechanism is a part used

to move contacts from open to closed

position or inversely.

Ex. Hydraulic Mechanism.

e). Control and auxiliary functions:  

The signal is sent to the coil to move a latch or open a valve leading to energy release of a mechanical drive

Classification of Breakers

DEAD Tank type Live tank type

Indoor Switchgear (GIS Outdoor breakers (AIS)

BREAKER'S OPERATION TIMES

• Basic oprns of the CB is "CLOSE" when joining, and "TRIP" when parting the contacts.• In most of the cases it has to execute on

demand a combination of the basic operations, called cycles. The most popular are the following:

1. "TRIP FREE", (C-O): simulates a trip on short circuit after a "CLOSE".

2. "RECLOSE", (O-C): simulates a fast close after short circuit trip to reestablish the current.

3. "RECLOSE-OPEN", (O-0.3s-C-O): Simulates a "RECLOSE" on short circuit. The breaker should clear the fault successfully.

4. (C-O)-15 sec-(C-O)-15-sec-(C-O): simulates a multiple close after short circuit trips in purpose of re-establishing the current, hoping that the short circuit is disappeared. This cycle is mostly used in the Medium voltage appls.

5. The times measured, for the different cycles starting from the coil energizing until the switching of the main contacts are called the Breaker's mechanical times of operations.

Testing of circuit breaker

• Type tests

– High power tests

• Direct tests

• synthetic tests

– Short circuit tests

– Switching performance tests

– High voltage tests

– Mechanical and environmental tests

– Temperature rise test

• Routine tests

– Mechanical operations test

– Measurement of contact resistance

– Voltage withstand test on control circuit

– Power frequency withstand test on main circuit

– High pressure test on Hydraulic mechanism

– SF6 gas tightness test

– Pump charging time for operations

– Leak testing hydraulic mechanism

– N2 leak test on accumulator

Circuit breakers with composite insulators

• Explosion proof• Light weight• Single piece of any length• No L/D constraint• Higher creapage can be achieved• Comparatively costly• No of joints can be reduced

Development of 245kV SF6 CB with Hydro Spring Mech.

• PRESENT MARKET PRICE: 13.5 Lakhs

• EXISTING BREAKER MATERIAL COST: 16.5 LAKHS

• NEW DESIGN WITH DTC MATERIAL COST: 8.5 LAKHS