Top 10 Switchgear Questions with Brief Explanatory Answers

Switchgear Questions with Answers

What is a fuse

A fuse is a short piece of metal that is inserted in the circuit, which melts when excessive current flows through it thus breaking the circuit.

What is a circuit breaker

A circuit breaker is a protection element which can make or break a circuit either manually or by remote control under normal conditions. It is intended to break a circuit automatically under fault conditions. A circuit breaker integrates manual/remote control/ automatic control for switching functions.

What do you mean by Arc voltage

It is defined as the voltage that appears across the contacts of the circuit breaker during the arcing period.

How length of arc affects arc resistance

The arc resistance is directly proportional to length of arc. The arc resistance increases with the length of the arc.

What does the term recovery voltage imply

It is defined as the normal frequency 50 Hz or 60 Hz values of RMS voltage that appears across the circuit breaker contacts after final arc extinction. It roughly equals the system voltage.

How many types of switchgear are there on basis of Voltage level

Switchgear is often classified into three types on the basis of voltage level for which it is designed.

• LV Switchgear – Rated for voltage under 1 kV
• MV Switchgear – Rated for voltage under 36 kV
• HV Switchgear – Rated for voltage above 36 kV

What do you mean by MVA breaking capacity of the circuit breaker

MVA breaking capacity of the circuit breaker is the product of short-circuit current (A) and normal rated service voltage.

What are SF6 Circuit Breakers

These are the circuit breakers which use sulphur hexaflouride (SF6) gas as the arc quenching medium.

How many types of unsymmetrical faults are there

Four types of unsymmetrical faults are there namely the

1. Line to line to line fault
2. Line to ground
3. Line to line
4. Double line to ground

What do you mean by Main and transfer bus bar arrangement?

This arrangement comprises a main bus that is used under ordinary conditions and a transformer bus for emergency purposes. The major advantage associated with this scheme is the use of single circuit breaker for tieing purposes. Such connection scheme is affordable with the main drawback involving complete shutdown of a substation in case of failure.