Quiz: Electrical Engineering 29 Apr 2021

Quiz: Electrical Engineering
Exam: DFCCIL
Topic: Switchgear and protection

Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

Q1. Reactance relay is used for protection in:
(a) Long transmission lines
(b) Short transmission lines
(c) Medium transmission lines
(d) Both long transmission lines and short transmission lines

Q2. Pilot relaying schemes are used for protection of
(a) Bus bars
(b) Transformers
(c) Transmission lines
(d) Instrument transformers

Q3. The percentage bias for a generator protection lies between
(a) 15 to 20 %
(b) 10 to 15 %
(c) 5 to 10 %
(d) None of these

Q4. Match List-I (power system component) with List-II (applications) and select the correct answer using codes given below the lists:

Codes:
A B C D
(a) 4 3 2 1
(b) 1 3 2 4
(c) 2 3 1 4
(d) 2 3 4 1

Q5. Current chopping is due to
(a) Interrupt of heavy capacitive currents
(b) Interrupt of bolted faults
(c) Interruption of low inductive currents
(d) Interruption of unity power factor loads

Q6. Current chopping usually occurs in
(a) Oil circuit breaker
(b) Minimum OCB
(c) MCB
(d) Air blast circuit breaker

Q7. The main function of a fuse —–
(a) protect the appliance
(b) prevent excessive currents
(c) open the circuit
(d) protect the line

Q8. Which of the following medium is employed for extinction of arc in air circuit breaker?
(a) Mineral Oil
(b) Air
(c) SF6
(d) Water

Q9. Which of the following relays are used in protection of medium transmission lines?
(a) Mho relays
(b) Admittance relays
(c) Impedance relays
(d) any of the above

Q10. The topmost wire in distribution systems is:
(a) Neutral wire
(b) Phase wire
(c) Earth wire
(d) None of these

SOLUTIONS
S1. Ans.(b)
Sol. Relay used for different configuration of transmission lines……
• Short transmission line: reactance relay
• Medium transmission line: impedance relay
• Long transmission line: mho relay

S2. Ans.(c)
Sol. Pilot relaying: for protection of transmission lines.

S3. Ans.(a)
Sol. The percentage bias for a generator protection lies between 15-20 %.

S4. Ans.(d)
Sol.
List-I (power system component) List-II (application)
A. Current transformer —-To feed the current coils of indicating and measuring instruments
B. Surge absorber —-To minimize the danger due to over-voltage
C. Earthing —-For providing safety to the users
D. Circuit breaker—– To carry full load current continuously

S5. Ans.(c)
Sol. Interruption of low inductive currents.

S6. Ans.(d)
Sol. Current chopping usually occurs in Air blast circuit breaker.
• Current Chopping in circuit breaker is defined as a phenomenon in which current is forcibly interrupted before the natural current zero.

S7. Ans.(b)
Sol. prevent excessive currents

S8. Ans.(b)
Sol. Air is used as extinguishing medium for air blast CB.

S9. Ans.(c)
Sol. Relays and their applications:

1. Admittance relays —– Short transmission lines
2. Impedance relays —— Medium transmission lines
3. Mho relays ————- Long transmission lines
   Impedance relays are used for protecting medium transmission lines in which arcing ground faults are less frequent.

S10. Ans.(c)
Sol.
• The topmost wire in distribution systems is Earth wire.
• Earth wire is used for protection against lightning.

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