🔌 Circuit Breakers & Switchgear
- What is / are the main disadvantage of using oil as the quenching medium in circuit breakers?
a. Need periodical replacement
b. Risk of formation of explosive mixture with air
c. Possibility of causing fire hazards
d. All of the above
Answer: d. All of the above - A three-phase, 33 kV oil circuit breaker is rated 1200 A, 2000 MVA, 3s. What is its symmetrical breaking current?
a. 1200 A
b. 3600 A
c. 35 kA
d. 104.8 kA
Answer: c. 35 kA - A thermal protection switch provides protection against what?
a. Overload
b. Temperature
c. Short circuit
d. Over voltage
Answer: a. Overload - Which of the following circuit breakers is used for the railway electrification?
a. Air blast circuit breaker
b. SF6 circuit breaker
c. Bulk oil circuit breaker
d. Minimum oil circuit breaker
Answer: a. Air blast circuit breaker - Which circuit breaker is preferred for extra high voltage AC systems?
a. Bulk oil type
b. Air blast
c. SF6 circuit breaker
d. Vacuum circuit breaker
Answer: c. SF6 circuit breaker - Which among these circuit breakers produce the least arc energy?
a. Plain oil
b. Minimum oil
c. Air blast
d. Air break
Answer: c. Air blast - The rating of the circuit breaker is usually determined on the basis of ____________ fault.
a. Symmetrical
b. Line to line
c. Single line to ground
d. Double line to ground
Answer: a. Symmetrical - Which type of circuit breaker is highly reliable and requires the least maintenance?
a. Oil circuit breakers
b. Air blast
c. Vacuum circuit breakers
d. SF6 circuit breakers
Answer: d. SF6 circuit breakers - Circuit breakers usually operate under:
a. Steady short circuit current
b. Sub transient state of short circuit current
c. Transient state of short circuit current
d. None of these
Answer: b. Sub transient state of short circuit current - What is the making capacity of the circuit breaker?
a. Less than the asymmetrical breaking capacity
b. Greater than the asymmetrical breaking capacity
c. Equal to the asymmetrical breaking capacity
d. Equal to the symmetrical breaking capacity
Answer: b. Greater than the asymmetrical breaking capacity - 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
Answer: d. 89 kA - The breaking capacity of a 3-phase CB is given by:
a. V × I × 10⁻⁶
b. √3 × V × I × 10⁻⁶
c. 1.1 × V × I × 10⁻⁶
d. √2 × V × I × 10⁻⁶
Answer: b. √3 × V × I × 10⁻⁶ - Assertion (A): In comparison to making capacity, the breaking capacity is higher.
Reason (R): Breaking capacity = √3 × V × I × 10⁻⁶
a. Both A and R are true, and R is the correct explanation
b. Both A and R are true, but R is not the correct explanation
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 - What is the making to breaking current ratio for an EHV circuit breaker?
a. More than 1
b. Equal to 1
c. Less than 1
d. A negative value
Answer: a. More than 1
⚙️ Isolators & Relays
- Why is an isolator installed?
a. To isolate a portion of the circuit
b. As a substitute for a circuit breaker
c. On either side of the circuit breaker
d. Both (a) and (c)
Answer: d. Both (a) and (c) - For which of the following are current ratings not required?
a. Circuit breakers
b. Relays
c. Isolators
d. Load break switch
Answer: c. Isolators - Isolators used in transmission lines are capable of breaking:
a. Fault current
b. No current
c. Charging current
d. Load current
Answer: c. Charging current - Isolators are used for:
a. Breaking abnormal current
b. Making under fault condition
c. Breaking the circuit under no-load condition
d. None of these
Answer: c. Breaking the circuit under no-load condition - Major cause of circuit breaker failure is:
a. Trip circuit open
b. Trip latch defective
c. Spring defective
d. All of these
Answer: d. All of these - What is the purpose of backup protection?
a. To increase speed
b. To increase reach
c. To eliminate blind spots
d. To guard against failure of primary
Answer: d. To guard against failure of primary - The actuating quantity for relays can be:
a. Magnitude
b. Frequency
c. Phase angle
d. All of these
Answer: d. All of these - Protective relays can be designed to respond to:
a. Light intensity
b. Impedance, resistance
c. Voltage and current
d. All of these
Answer: d. All of these - Operating speed of a relay depends on:
a. Rate of flux build-up
b. Armature core air gap
c. Spring tension
d. All of these
Answer: d. All of these - In the protection scheme, what does the first part consist of?
a. Primary winding of CT in series
b. Secondary of CT and operating coil
c. Tripping circuit
d. None of these
Answer: a. Primary winding of CT in series - The third part of a relay circuit consists of:
a. Primary CT winding
b. CT secondary and operating coil
c. Tripping circuit
d. Bus bar
Answer: c. Tripping circuit - Which component ensures the safety of the line?
a. Relay
b. Circuit breaker
c. Bus bar
d. Current transformer
Answer: a. Relay - The tripping circuit is:
a. AC
b. DC
c. Either AC or DC
d. None
Answer: c. Either AC or DC - Plug setting of an electromagnetic relay can be altered by:
a. Number of ampere turns
b. Air gap
c. Back stop
d. None
Answer: a. Number of ampere turns - Most efficient torque-producing structure in induction-type relays:
a. Shaded pole
b. Watt-hour meter
c. Induction cup
d. Induction loop
Answer: c. Induction cup - Which circuit breaker has the lowest operating voltage?
a. SF6
b. Air break
c. Air blast
d. Minimum oil
Answer: b. Air break
🔁 Extra Practice Questions for SSC JE EE
- The main advantage of vacuum circuit breaker is:
a. Silent operation
b. Least contact erosion
c. High arc energy
d. None
Answer: b. Least contact erosion - SF6 gas is preferred because it is:
a. Electronegative
b. Inert and heavy
c. Non-inflammable
d. All of the above
Answer: d. All of the above - Arc interruption in vacuum circuit breaker takes place at:
a. Peak voltage
b. Current zero
c. Power factor angle
d. All of the above
Answer: b. Current zero
🔥 Fuse – MCQs with Answers for SSC JE
- What is the primary function of a fuse in an electrical circuit?
a. To increase voltage
b. To protect against overload and short circuit
c. To maintain power factor
d. To act as a switch
Answer: b. To protect against overload and short circuit - A fuse wire should have:
a. Low melting point and high conductivity
b. High melting point and low conductivity
c. Low melting point and low conductivity
d. High melting point and high conductivity
Answer: c. Low melting point and low conductivity - Which material is commonly used for making fuse elements?
a. Copper
b. Silver
c. Tin-lead alloy
d. All of the above
Answer: d. All of the above - In a fuse, the fusing current is:
a. The current at which fuse melts
b. The rated current
c. Less than rated current
d. The minimum current needed for circuit operation
Answer: a. The current at which fuse melts - Which of the following statements is correct?
a. A fuse is reusable
b. Fuse operation is slow compared to MCB
c. Fuse works on the electromagnetic principle
d. Fuse automatically resets after fault
Answer: b. Fuse operation is slow compared to MCB - What will happen if a fuse with a higher current rating is used instead of the required one?
a. It will protect the circuit better
b. It will blow early
c. It may not protect the circuit during faults
d. It increases power consumption
Answer: c. It may not protect the circuit during faults - The breaking capacity of a fuse is:
a. Maximum current it can carry normally
b. Minimum current it can interrupt
c. Maximum fault current it can safely interrupt
d. Rated current of fuse
Answer: c. Maximum fault current it can safely interrupt - Which one is a disadvantage of a fuse?
a. Low cost
b. Simple operation
c. Once blown, needs replacement
d. Fast operation
Answer: c. Once blown, needs replacement - The inverse time characteristic of a fuse means:
a. Fuse blows instantly for all overloads
b. Higher the current, shorter the blowing time
c. Lower the current, shorter the blowing time
d. Blowing time is constant for all currents
Answer: b. Higher the current, shorter the blowing time - Which fuse is used for low voltage household applications?
a. HRC fuse
b. Cartridge fuse
c. Kit-kat fuse
d. Rewireable fuse
Answer: d. Rewireable fuse