SWITCHGEAR

1.       What are the techniques employed to extinguish the arc in AC circuit breaker?

1)      High resistance interruption.

2)      Low resistance or zero point interruption are gets extinguished at natural current zero of AC wave and is prevented from restarting again by rapid buildup of di-electric strength of contact space.

2.       What is Antipump relay?

A feature in corperated in the circuit breaker or reclose scheme whereby in the event of a permanent fault repeated operations of the circuit breaker are prevented when the closing impulse is longer than the seem of the protective relay and circuit breaker operating times.

3.       How can you ensure vacuum level inside the vacuum bottle?

1)     Vacuum Gauge

2)      By applying power frequency high voltage test.

4.       What are the important checks or OCB’s during maintenance

1)      Check insulation resistance of each pole phase to phase/phase to ground.

2)      Check di-electric strength of oil and oil level

3)      Check mechanical operations

4)      Clean insulators

5)      Check contact length and simultaneous contacts terminal

6)      Measure contact resistance.

5.       What are the types of Circuit Breakers?

a)      MCB – Miniature Circuit Breakers

b)      MCCB – Molded case Circuit Breaker

c)       OCB – Oil Circuit Breaker

d)      MOCB – Minimum oil circuit breaker

e)      ACB – Air Circuit Breaker

f)       VCB – Vacuum Circuit Breaker

g)      SF6 – Sulphur Hexa Fluoride circuit breaker

6.       How do you carry out the yearly preventive maintenance of VCB?

a)      Obtain the permit

b)      Transfer the load of breaker

c)       Switch OFF and Rack Out breaker

d)      Discharge spring already

e)      Physically clean the V.C.B.

f)       Check and clean the finger contact

g)      Check the mechanism and apply grease

h)      Rack-in the breaker in test position

i)        Electrically on the breaker three times for trial

j)        Rack in the breaker in service position and give the load

k)      Close the permit

7.       How do you carry out the maintenance of A.C.B.?

a)      Obtain Work Permit

b)      Transfer the load of breaker

c)       Rack out the breaker and discharge the spring and already charged

d)      Physically clean the A.C.B.

e)      Open the Arc check, Check and clean the fixed and moving contacts

f)       Check and clean the finger contacts

g)      Check the mechanism and grease it

h)      Rack in the breaker in test position

i)        Switch “ON” and “OFF” the breaker electrically for trial

j)        Rack in the breaker in service position

k)      Energize the breaker

l)        Close the permit.

8.       What maintenance required on oil circuit breakers?

a)      Check all circuit carrying parts and attend to the arcing contact

b)      Test the oil and change it if it is bad

c)       Inspect the insulation for possible damage

                        d)   Check closing and tripping mechanism