Question 1

The main function of a fuse is to
A)protect the line
B)open the circuit
C)protect the appliance
D)prevent excessive currents

Accepted Answer

The main function of a fuse is to prevent excessive currents by breaking the circuit when the current exceeds a certain level, thereby protecting the circuit and appliances from damage.

Question 2

On which of the following routine tests are conducted ?
A)Oil circuit breakers
B)Air blast circuit breakers
C)Minimum oil circuit breakers
D)All of the above

Accepted Answer

Routine tests are conducted on all types of circuit breakers, including oil circuit breakers, air blast circuit breakers, and minimum oil circuit breakers, to ensure their reliability and safety in operation.

Question 3

SF6 gas
A)is yellow in colour
B)is lighter than air
C)is nontoxic
D)has pungent small

Accepted Answer

SF6 (sulfur hexafluoride) is an inert, non-toxic gas. It is colorless, odorless, and heavier than air, making options A, B, and D incorrect.

Question 4

The arcing contacts in a circuit breaker are made of
A)copper tungsten alloy
B)porcelain
C)electrolytic copper
D)aluminium alloy

Accepted Answer

Copper tungsten alloy is used for arcing contacts in circuit breakers due to its high melting point, excellent conductivity, and resistance to welding and erosion under arcing conditions.

Question 5

Which of the following medium is employed for extinction of arc in air circuit breaker ?
A)Water
B)Oil
C)Air
D)SF6

Accepted Answer

Air circuit breakers use air as the medium for arc extinction. The arc is extinguished by creating an arc chute where the arc is lengthened, cooled, and split, thus extinguishing it effectively.

Question 6

With which of the following, a circuit breaker must be equipped for remote operation ?
A)Inverse time trip
B)Time-delay trip
C)Shunt trip
D)None of the above

Accepted Answer

A circuit breaker must be equipped with a shunt trip for remote operation. A shunt trip allows the circuit breaker to be tripped (opened) remotely by applying an external control voltage, which is essential for remote control and automation systems.

Question 7

Fault diverters are basically
A)fuses
B)relays
C)fast switches
D)circuit breakers

Accepted Answer

Fault diverters are essentially fast switches designed to quickly redirect electrical current in the event of a fault, protecting the system from damage.

Question 8

A thermal protection switch can protect against
A)short-circuit
B)temperature
C)overload
D)over voltage

Accepted Answer

The answer of A thermal protection switch can protect against
A)short-circuit
B)temperature
C)overload
D)over...

Question 9

Arc in a circuit behaves as
A)a capackive reactance
B)an inductive reactance
C)a resistance increasing with voltage rise across the arc
D)a resistance decreasing with voltage rise across the arc

Accepted Answer

An arc in a circuit behaves as a resistance that decreases with an increase in voltage across the arc, due to the ionization of gases which facilitates current flow.

Question 10

Thermal circuit breaker has
A)delayed trip action
B)instantaneous trip action
C)both of the above
D)none of the above

Accepted Answer

Thermal circuit breakers have a delayed trip action because they rely on the heat generated by the current to bend a bimetallic strip, which takes time to respond to overcurrent conditions.

Question 11

Thermal overload relays are used to protect the motor against over current due to
A)short-circuits
B)heavy loads
C)grounds
D)all of the above

Accepted Answer

Thermal overload relays are specifically designed to protect motors from overcurrent that can occur due to heavy loads. They work by sensing the heat generated by the excessive current flow, which can damage the motor if it continues for too long. Short-circuits and grounds are typically handled by other protective devices like circuit breakers and ground fault interrupters.

Question 12

Magnetic circuit breaker has ______ trip action.
A)delayed
B)instantaneous
C)both of the above
D)none of the above

Accepted Answer

Magnetic circuit breakers have an instantaneous trip action, as they rely on the magnetic force generated by the current to trip the breaker immediately when the current exceeds a certain threshold.

Question 13

D.C. shunt relays are made of
A)few turns of thin wire
B)few turns of thick wire
C)many turns of thin wire
D)many turns of thick wire

Accepted Answer

D.C. shunt relays are made of many turns of thin wire to create a high resistance coil suitable for shunt applications.

Question 14

The relay operating speed depends upon
A)the spring tension
B)the rate of flux built up
C)armature core air gap
D)all of the above

Accepted Answer

The relay operating speed is influenced by multiple factors including the spring tension, the rate of flux built up, and the armature core air gap. Each of these elements affects how quickly the relay can respond to changes, thus impacting its overall operating speed.

Question 15

In order that current should flow without causing excessive heating or voltage drop, the relay contacts should
A)have low contact resistance
B)be clean and smooth
C)be of sufficient size and proper shape
D)have all above properties

Accepted Answer

All the mentioned properties are important to ensure that relay contacts can conduct current efficiently without excessive heating or voltage drop. Low contact resistance, cleanliness, smoothness, and appropriate size and shape all contribute to optimal performance.

Question 16

Circuit breakers usually operate under
A)transient state of short-circuit current
B)sub-transient state of short-circuit current
C)steady state of short-circuit current
D)after D.C. component has ceased

Accepted Answer

Circuit breakers are designed to operate during the transient state of short-circuit current to quickly interrupt the fault and protect the system.

Question 17

Circuit breakers are essentially
A)current carrying contacts called electrodes
B)arc extinguishers
C)circuits to break the system
D)transformers to isolate the two systems

Accepted Answer

Circuit breakers are devices that interrupt current flow in an electrical circuit, and they use current carrying contacts called electrodes to achieve this function.

Question 18

The current zero interruption, in oil and air blast circuit breakers, is achieved by
A)lengthening of the gap
B)cooling and blast effect
C)both (A) and (B)
D)deionizing the oil with forced air

Accepted Answer

The current zero interruption in oil and air blast circuit breakers is achieved by both lengthening of the gap and the cooling and blast effect. Lengthening the gap increases the distance the arc must travel, and the cooling and blast effect rapidly cools and extinguishes the arc.

Question 19

Air blast circuit breaker is used for
A)over currents
B)short duty
C)intermittant duty
D)repeated duty

Accepted Answer

Air blast circuit breakers are used for repeated duty because they can quickly extinguish arcs and are suitable for frequent operation.

Question 20

An efficient and a well designed protective relaying should have
A)good selectivity and reliability
B)economy and simplicity
C)high speed and selectivity
D)all of the above

Accepted Answer

An efficient and well-designed protective relaying system should encompass all these attributes: good selectivity and reliability, economy and simplicity, and high speed and selectivity to ensure effective protection and operation.

Quiz 1: Electrical Protection and Circuit Breakers

The main function of a fuse is to

On which of the following routine tests are conducted ?

SF6 gas

The arcing contacts in a circuit breaker are made of

Which of the following medium is employed for extinction of arc in air circuit breaker ?

With which of the following, a circuit breaker must be equipped for remote operation ?

Fault diverters are basically

A thermal protection switch can protect against

Arc in a circuit behaves as

Thermal circuit breaker has

Thermal overload relays are used to protect the motor against over current due to

Magnetic circuit breaker has ______ trip action.

D.C. shunt relays are made of

The relay operating speed depends upon

In order that current should flow without causing excessive heating or voltage drop, the relay contacts should

Circuit breakers usually operate under

Circuit breakers are essentially

The current zero interruption, in oil and air blast circuit breakers, is achieved by

Air blast circuit breaker is used for

An efficient and a well designed protective relaying should have