Quiz: Electrical Engineering 28 Apr 2021

Quiz: Electrical Engineering
Exam: DFCCIL
Topic: Power generation, transmission and distribution

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

Q1. As a matter of economy, voltage for power transmission should be
(a) low
(b) medium
(c) high
(d) none of the above

Q2. When transmission voltage is increased, the line losses are
(a) decreased
(b) increased
(c) same
(d) none of the above

Q3. If voltage is increased by n times, the size of the conductor would
(a) increase by n times
(b) reduce by 1/n times
(c) increase by n² times
(d) reduce by 1/n² times

Q4. What is the value of charging current in short transmission lines?
(a) Less than medium transmission lines
(b) Equal to medium transmission lines
(c) More than medium transmission lines
(d) More than long transmission lines

Q5. Voltage regulation of a transmission line should be __
(a) Minimum
(b) Maximum
(c) Greater than 50 %
(d) Less than 50 %

Q6. The operating voltage of super tension cable is
(a) 1 – 11 kV
(b) 11 – 33 kV
(c) 33 – 66 kV
(d) Above 66 kV

Q7. The voltage of the single-phase supply to residential consumers is
(a) 110 V
(b) 230 V
(c) 440 V
(d) Any of the above

Q8. The voltage regulation of flat voltage profile system is
(a) 100 %
(b) 50 %
(c) 0 %
(d) Any of the above

Q9. The charging current drawn by the cable is
(a) Lags voltage by 90⁰
(b) Lead voltage by 90⁰
(c) Lead voltage by 45⁰
(d) None of the above

Q10. 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) All of the above

SOLUTIONS

S1. Ans.(c)
Sol. Transmission of electric power at high voltages has many advantages including less conductor material required, reduced line losses and decrease in percentage line drop.

S2. Ans.(a)
Sol. P=√3 VI cosϕ or I=P/(√3 V cosϕ)
As transmission voltage V increases, the line current I and hence line losses are decreased.

S3. Ans.(d)
Sol. Area of cross-section of conductor ∝ 1/V².

S4. Ans.(a)
Sol. Line to Earth capacitance of short transmission line is less than that in medium and long transmission line and is negligible. Because of this the charging current of short transmission line is less than that in medium and long transmission line and is negligible.

S5. Ans.(a)
Sol. More value of voltage regulation means more voltage fluctuations and this is undesirable. So, the value of voltage regulation should be as low as possible.

S6. Ans.(b)
Sol.
Type of cable Operating voltage
Low tension <1 KV
High tension 1-11 KV
Super tension 11-33 KV
Extra high tension <66 KV

S7. Ans.(b)
Sol. 230 V

S8. Ans.(c)
Sol. The % voltage regulation is given as (Vs-Vr)/Vr*100.
For flat voltage profile system all the voltage drop in the line are neglected therefore supply voltage (Vs) is equal to the Receiving end voltage (Vr) i.e Vs = Vr.
Hence the voltage regulation for flat voltage profile system is zero.

S9. Ans.(b)
Sol. The charging current drawn by the cable is capacitive in nature, therefore, it leads the voltage by 90⁰.

S10. Ans.(c)
Sol. Shunt trips are used to open the circuit breaker contacts by energizing the solenoid from an external source.

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