HV Equipment File 4 of 5

8/14/2019 HV Equipment File 4 of 5

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POWER CIRCUIT BREAKER (ANSI Std. C37.06)


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A device, that can be able to breaking, making, carrying current

both during normal and fault condition

During interruption, fault current flows through circuit breaker

contact while it tries to open. This current can not cease

suddenly. Therefore high electric field and thermal stress aroundcontact surface occur and cause ionisation of oil or gas nearby

and after that arc occurs. The resistance of arc depends on its

length, which is important for arc extinguishing method.

Gas Flow

Electric ArcElectrical

system

Electric and

Magnetic Field

Operating

Mechanism

Radiation

Turbulence

Gas mixture


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In most circuit breaker except vacuum type, current interruptionneeds to increase the length of arc in order to increase the

resistance. This arc will extinguish when current passes zero

crossing and contact completely open.


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Circuit breaker type

1) Vacuum CB

Interrupter is in enclosed chamber with very low air pressure. No

ionisation inside, only metal contact evaporation occurs, then it has

small contact gap with quick insulation recovery.


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2) SF6 CB

3 types

Magnetic Type Interrupter

Puffer Type Interrupter

Self blast Interrupter

Magnetic type is used for V < 15kV and low current rating.

It uses magnetic force to lengthen ionised gas plasma to mix

with normal gas.

Puffer type compresses gas in cylinder and flows through

nozzle to increase the arc length and replace ionised gas.

Live tank circuit breaker


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SINGLE PRESSURE PUFFER TYPE INTERRUPTER

1. Fixed contact2. Insulating nozzle

3. Arcing contact

4. Compression chamber

5. Fixed piston


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Dead tank circuit breaker

Nozzle blows gas to arc (20,000K) and dissipate heat by convection and

conduction (arc contacts with nozzle wall).

Nozzle before is made of graphite, nowadays by Teflon to reduce/avoid

high conductivity metallic contamination of the gas plasma.


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Self blast circuit breaker

Advantages

Reduction of mechanism requirement.

Contact speed depends on required operating time

Higher fault current, higher pressure, then easy to interrupt Soft interruption characteristics at low fault current


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Phase 1. Opening of main contact

Circuit Breaker Opening


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Phase 2. Current commutation to arcing contact


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Phase 3. Arcing contact opening

t

i.


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Phase 4. Arcing phenomena


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Phase 5. High current phase

t

i.


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Phase 6. Extinguishing phase


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Phase 7. End phase

t

i.


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Closing operation

Arc occurs only at arcing contact.


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Interrupting chamber design


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CB TECHNICAL DATA

- Nominal Voltage

- Highest Voltage (1.1 times of Nominal System Voltage)

- Rated Continuous Current

- Frequency

- Duty Cycle operating cycle of CB is 2 times closing and

opening within 0.3 and 15 s time interval. (CO - 0.3S - CO

- 15S - CO)


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- Interrupting Current

Example CB with 15kVmax and Isc = 37 kA has K

Factor = 1.3 means that between voltage 15/1.3=11.5 kV

and 15 kV, interrupting rating is directly proportional to

operating voltage.

Then at 12.5 kV, the rms value of symmetrical interrupting

rating = 15/12.5 x 37 = 44.4 kA. This means symmetricalinterrupting capacity is higher than S/C rating with ratio of

rated max voltage to operating voltage.


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- Interrupting Time

- Distribution 5 Cycles- Transmission 3 Cycles

- EHV 2 Cycles

- 1 Minute Power Frequency Test- Impulse Withstand Voltage

- Short Circuit Breaking Current

- Total Break Time, Total Closing Time- Pre - Closing Resistor in parallel with interrupter to

limit over voltage during closing no load line with 6 - 15

ms connecting time.- Voltage Gradient Capacitor for breaker with multi

break in parallel with interrupters for equal voltage dropacross each interrupters during interruption.


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- 3 Pole or 1 Pole 1 Pole mostly for V > 145 kV. Each

pole trip independently with one per 1 pole to increase systemstability.


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C i i


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Current interruption

During arcing, thermal race of SF6 with higher heat capacity to absorb

thermal energy from arc = mass density x Enthalpy x sound velocity.

Recovery voltage need good dielectric recovery. Dielectric recoveryrate > dV/dt of recovery voltage (RRRV).

1


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Transient Recovery Voltage ( TRV ) LCf

2

1=

( ) ( ) ( )

+

+

= tet

LR

mV

ti

sinsin

222

R

L)tan(and

==

L

R


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Operating mechanism

Manual operation

Solenoid operation

Motor charge spring

Hydraulic

Pneumatic

25 %26 %

6 %

43 %

Major failure mode of SF6

single pressure circuit breaker

Operating Mechanism

HV Components

Other causes

Elec. Control & Aux. circuit

Insulation to ground

Percentage of each failure in HV components

4 %

51 %

45 %

Aux. interrupters,

resistors

Interrupters

HV Equipment File 4 of 5

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