# Making & Breaking Capacity of Circuit Breakers

## Making & Breaking Capacity of Circuit Breakers

Q1. What is the making capacity of the circuit breaker?

a. Less than the asymmetrical breaking capacity of the breaker.
b. Greater than the asymmetrical breaking capacity of the breaker.
c. Equal to the asymmetrical breaking capacity of the breaker.
d. Equal to the symmetrical breaking capacity of the breaker.

ANSWER: b. Greater than the asymmetrical breaking capacity of the breaker.

Q2. A three phase circuit breaker is rated 2000 MVA, 33 kV. What will be its making current?

a. 35 kA
b. 49 kA
c. 70 kA
d. 89 kA

Q3. The breaking capacity of a three phase circuit breaker is given by

a. Service line voltage * rated symmetrical current in amperes * 10-6 MVA
b. √3 * Service line voltage * rated symmetrical current in amperes * 10-6 MVA
c. 1.1* Service line voltage * rated symmetrical current in amperes * 10-6 MVA
d. √2 * Service line voltage * rated symmetrical current in amperes * 10-6 MVA

ANSWER: b. √3 * Service line voltage * rated symmetrical current in amperes * 10-6 MVA

Q4. Assertion (A): In comparison to making capacity of a circuit breaker its breaking capacity is normally higher.
Reason (R): The breaking capacity of a CB is expressed as √3 * VI * 10-6 MVA

a. Both A and R are true and R is the correct explanation of A
b. Both A and R are true and R is not the explanation of A
c. A is true but R is false
d. A is false but R is true.

ANSWER: d. A is false but R is true.

Q5. What is the making to breaking current ratio for an extra high voltage circuit breaker?

a. More than 1
b. Equal to 1
c. Less than 1
d. A negative value