High Voltage Circuit Breakers

Question 1

What are the five most common types of circuit-breakers found in High Voltage installations?

Answer 1

1. Air Magnetic
2. Vacuum
3. Oil
4. Air Blast
5. Sulpher Hexaflouride (SF6)

Question 2

What does a puffer do in an air magnetic circuit breaker?

Answer 2

It blows air into the arc as the contacts part to assist in arc extinction.

Question 3

Bulk-oil circuit breakers are large and take up a lot of space, and are gradually being phased out of use for what reasons? (3)

Answer 3

1. Oil is a flammable substance
2. Oil is subject to contamination
3. Leakage results in serious environmental problem

Question 4

The air-blast circuit breaker uses air as the insulating, arc-quenching, and actuating force that closes and opens the contacts. What are some of the cons? (3)

Answer 4

1. The air must be kept clean and dry
2. It is costly since it requires filters, exhaust coolers and silencers.
3. It has loud operational noise and is used outdoors

Question 5

Sulphur hexafluoride (SF6) gas, which has high dielectric strength and high thermal conductivity is used as the insulating and arc-quenching medium for circuit breakers. They are expensive, but what benefits do they have? (5)

Answer 5

1. Reliability
2. Low maintenance
3. Small and compact size
4. Use a non-combustible, non-toxic, inert gas (SF6 )
5. Gas is kept at a low pressure relative to the air-blast CB