1.
What are the ratings required to be specified
for HV circuit breaker?
1.
Rated voltage
2.
Rated insulation level
3.
Rated normal current
4.
Rated frequency
5.
Rated duration of short time current
6.
Rated short circuit breaking current
7.
Rated short circuit making current
8.
Rated peak with stand current
9.
Rated TRV (Transit Recovery Voltage for terminal
fault)
2.
What is meant by short circuit breaking current?
The rated short circuit
breaking current of circuit breaker is the highest values of short circuit
current which a circuit breaker is capable of breaking under specified
condition of transient recovery voltage and power frequency voltage. Expressed
in K. A. RMS at contact separation.
3.
What is meant by short circuit making current?
Rated making current = 1.8 × root 2 × rated short circuit
breaking current.
=
2.5 × rated short circuit breaking current.
4.
What is rated short time current (duration of
short circuit)?
It is the R.M.S. value of
current that the circuit breaker can carry in a fully closed position during a
specified time under prescribed conditions of use and behavior.
Expressed as KA for period
of 1 second or 3 seconds.
5. 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.
6. 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.
7. How
can you ensure vacuum level inside the vacuum bottle?
1)
Vacuum Gauge
2)
By applying power frequency high voltage test.
8. 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.
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