Breakers

Breakers

A Circuit Breaker is a device, which can make (or) break the circuit either manually or by remote control i.e electrically by means of LT DC supply.  Break the circuit (or) disconnect the faulty circuit automatically under fault conditions.

            A circuit breaker essentially consists of fixed and moving contacts.  Under normal operation conditions the two contacts are closed. But at faulty condition the two contacts are open and separate the faulty circuit from healthy one. When a fault occurs at any part of the system, the secondary currents of the Current Transformers connected in series with the circuit flows through the relay current coils and picks up/energizes the breaker trip coil and operates the breaker by beans of some mechanical arrangement i.e opens the circuit contacts in the breaker.

            At the time of separation of the electrical male and female contacts, the continuous current due to raising voltage between contacts, but it will suppressed by means of high pressured interrupting media i.e Oil, SFG6 Gas, forced air, etc.

            33KV,132KV, 220KV, 400KV Sub-Station, 3 types of CB’s are used.

 They are

1.       VCB (Vacuum Circuit Breaker)

2.      SF6 Circuit Breaker

3.      Oil Circuit Breaker [now a days not using]

Vacuum Circuit Breaker:

            Vacuum has highest insulating strength.  The two contacts of circuit breaker are placed in the Evacuated chamber or vacuumed bottle.  The bottle is evacuated to high vacuum of the order of 10mm of mercury.  High vacuum has high dielectric strength and is a good arc extinguishing medium.

            Vacuum Circuit Breaker is a triple or multi pole circuit breaker whose extinguishing bottle is vacuum type.  The movements of the contacts take place inside the bottle.  It consists of fixed and moving contacts enclosed by shield area in the vacuumed bottle.  The arc shield retains the dielectric strength.  The moving member is connected to stainless steel to eliminate the possibility to air leak from the atmosphere. 

            When the breaker operates the moving and fixed contacts are separated and an arc tends strike between the contacts due to the ionization of metal ions by force of raising high electrical voltage between the contacts. The vacuum CB’s are practically always interrupts at the first current zero. The dielectric recovery of the vacuum of the vacuum and gas is extremely fast.

                                         

Example electrical specifications: 

Make                                       : BHEL

Type                                        : PVN 36

Sl. No.                                     : 12345

Year of Manufacture              : 2012-13

Rated Voltage                         : 36KV

Frequency                               : 50Hz

Rated Short Time Current      : 25KA

Breaking Capacity                  : 25KAP

Making Capacity                     : 62.5KAP

Rated Amps                            : 1250 amp

Shunt trip                                : 230V DC

Shunt close                              : 230V DC

Specification                           : IEC-62271-100

SF6 Circuit Breaker:

            Sulfur Hexa Fluoride gas (SF6) has high electrical insulating characteristics and also having excellent arc quenching capability. So SF6 gas is used in the circuit breaker known as SF6 circuit breaker.SF6 gas is maintained at rated pressure according the voltage of the system and fault currents [I.e measure of surge impudence loading]. E.g for 132KV SF6 breaker of make ABB has rated SF6 pressure is 7.0Kg/cm^2.  SF6 gas is the one of most stable compound, inert, no inflammable, non-hazardous and odorless. The density of SF6 gas is at about 5 times that of the air and heat dissipation in it is also much more than the air. The dielectric strength is about 2.4 times that of air.

EXAMPLE FOR ELECTRICAL SPECIFICATIONS OF 132KV LINE BREAKER

Make                           : ABB

WO.NO                      : TH SL SH 200101

S.no                             : 2345

Type                            : ELFSF 2-1(R)

Year of mfg                : 1992

Voltage                       : 145KV

IL                                : 275/E30KV

VW                             : 650KV

VA                              : 220DC

IN                                : 1600A

ISC                              : 31.5KA

IF                                : 50A

Pressure SF₆                 : 7.0 bar at 20⁰C

Pressure Air                 : 22.0 bar

Tth                               : 3.0 Sec

Frequency                   : 50Hz

Weight Of the breaker : 1700Kg

 [Attention: check the oil level in compressor for every 7 days]

For 33kv feeders, vacuum circuit breakers are used and for 132kv feeders, SF6 C.B’s are used.

           Pneumatic pressure operating mechanisms were used old model some of manufacturers like ABB and CGL but they are also supplying spring charging mechanisms of all breakers from 11KV electrical potential to 400KV Potential.  

    The breakers [i.e high voltage switches] using in the EHT sub-stations at various levels of voltages like 400KV,220KV, 132KV, 66KV,33KV and 11KV. The breakers are electrical switches with sophisticated features. The breakers are assembled with solid mechanism, erection structure and interrupting unit enclosed and supported by porcelain insulators. The insulators of the breaker are suitable for withstanding against the voltage level of the electrical system.

   The breakers are used to make or break the high level ranges of currents safely. Mainly the mechanism of the breaker is speed and accurately operative by heavy gauge mechanical springs or pneumatic pressure and controlled by controlling DC circuits externally by trip and close coils of the mechanical triggers. In other hand the interrupting unit plays main role to make or break the circuit at any condition of the loads.

    Now days for above 33KV voltage levels, the SF6 gas is used as interrupting media filled in the interrupting unit or bottle. The vacuum interrupters are used in the breakers for 33V, 11KV voltage levels.

  

Physical view of the 132KV SF6 breaker mechanism 

A Circuit Breaker is a device, which can make (or) break the circuit either manually or by remote control i.e electrically by means of LT DC supply.  Break the circuit (or) disconnect the faulty circuit automatically under fault conditions.

            A circuit breaker essentially consists of fixed and moving contacts.  Under normal operation conditions the two contacts are closed. But at faulty condition the two contacts are open and separate the faulty circuit from healthy one. When a fault occurs at any part of the system, the secondary currents of the Current Transformers connected in series with the circuit flows through the relay current coils and picks up/energizes the breaker trip coil and operates the breaker by beans of some mechanical arrangement i.e opens the circuit contacts in the breaker.

            At the time of separation of the electrical male and female contacts, the continuous current due to raising voltage between contacts, but it will suppressed by means of high pressured interrupting media i.e Oil, SFG6 Gas, forced air, etc.

            33KV,132KV, 220KV, 400KV Sub-Station, 3 types of CB’s are used.

 They are

1.       VCB (Vacuum Circuit Breaker)

2.      SF6 Circuit Breaker

3.      Oil Circuit Breaker [now a days not using]

Vacuum Circuit Breaker:

            Vacuum has highest insulating strength.  The two contacts of circuit breaker are placed in the Evacuated chamber or vacuumed bottle.  The bottle is evacuated to high vacuum of the order of 10mm of mercury.  High vacuum has high dielectric strength and is a good arc extinguishing medium.

            Vacuum Circuit Breaker is a triple or multi pole circuit breaker whose extinguishing bottle is vacuum type.  The movements of the contacts take place inside the bottle.  It consists of fixed and moving contacts enclosed by shield area in the vacuumed bottle.  The arc shield retains the dielectric strength.  The moving member is connected to stainless steel to eliminate the possibility to air leak from the atmosphere. 

            When the breaker operates the moving and fixed contacts are separated and an arc tends strike between the contacts due to the ionization of metal ions by force of raising high electrical voltage between the contacts. The vacuum CB’s are practically always interrupts at the first current zero. The dielectric recovery of the vacuum of the vacuum and gas is extremely fast.

                                         

Example electrical specifications: 

Make                                       : BHEL

Type                                        : PVN 36

Sl. No.                                     : 12345

Year of Manufacture              : 2012-13

Rated Voltage                         : 36KV

Frequency                               : 50Hz

Rated Short Time Current      : 25KA

Breaking Capacity                  : 25KAP

Making Capacity                     : 62.5KAP

Rated Amps                            : 1250 amp

Shunt trip                                : 230V DC

Shunt close                              : 230V DC

Specification                           : IEC-62271-100

SF6 Circuit Breaker:

            Sulfur Hexa Fluoride gas (SF6) has high electrical insulating characteristics and also having excellent arc quenching capability. So SF6 gas is used in the circuit breaker known as SF6 circuit breaker.SF6 gas is maintained at rated pressure according the voltage of the system and fault currents [I.e measure of surge impudence loading]. E.g for 132KV SF6 breaker of make ABB has rated SF6 pressure is 7.0Kg/cm^2.  SF6 gas is the one of most stable compound, inert, no inflammable, non-hazardous and odorless. The density of SF6 gas is at about 5 times that of the air and heat dissipation in it is also much more than the air. The dielectric strength is about 2.4 times that of air.

EXAMPLE FOR ELECTRICAL SPECIFICATIONS OF 132KV LINE BREAKER

Customer APSEB                                                                                                                               Make                           : ABB

WO.NO                      : TH SL SH 200101

S.no                             : 2345

Type                            : ELFSF 2-1(R)

Year of mfg                : 1992

Voltage                       : 145KV

IL                                : 275/E30KV

VW                             : 650KV

VA                              : 220DC

IN                                : 1600A

ISC                              : 31.5KA

IF                                : 50A

Pressure SF₆                 : 7.0 bar at 20⁰C

Pressure Air                 : 22.0 bar

Tth                               : 3.0 Sec

Frequency                   : 50Hz

Weight Of the breaker            : 1700Kg

 [Attention: check the oil level in compressor for every 7 days]

For 33kv feeders, vacuum circuit breakers are used and for 132kv feeders, SF6 C.B’s are used.

           Spring charging mechanism used in circuit breakers for 33kv and