# Power Systems Questions and Answers – Geometric Mean Distance and Geometric Mean Radius – 1

This set of Power Systems Multiple Choice Questions & Answers (MCQs) focuses on “Geometric Mean Distance and Geometric Mean Radius – 1”.

1. Which of the system would require more insulation, a 400 kV ac line or 400 kV dc line?
a) 400 kV ac
b) 400 kV dc
c) Both will need same level of insulation
d) Data is insufficient to decide

Explanation: In ac system, the peak value attained will be 400*√2= 564 kV.

2. The amount of dc compensation needed by a 400 kV dc line for transmitting the data over 300 km having resistance as 5 ohms?
a) 400 var
b) 564 var
c) 600 VAR
d) None of the mentioned

Explanation: A dc line does not require any reactive compensation.

3. Steady state problem is not very serious problem in dc transmission line system due to which of the following systems?
a) No reactive compensation
b) Only resistance drop
c) Stable voltage regulation
d) No reactive compensation, resistance drop, voltage regulation

Explanation: Due to all the above reasons, mainly the reactive power compensation there is very less variation in stability.

4. DC line transmission can be used to provide _______ link.
a) asynchronous
b) synchronous
c) lossless
d) none of the mentioned

Explanation: As dc link provides to connect to different frequencies of the operating buses. It can transfer power frequency independent.

5. (i) Low short circuit current is required in dc system
(ii) Fast control of the converter switches cannot effectively control the damping of the oscillations.
Choose the most appropriate.
a) (i) and (ii) both are true
b) Only (ii) is false
c) Only (i) is false
d) Both statements are false

Explanation: It’s an advantage the using converters in dc link can control the fast damping of the oscillations which occur in ac systems.
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6. The reactive power demand of the converters in HVDC can be provided by ___________
a) AC filters
b) Shunt Capacitors
c) SVC
d) AC Filters, Shunt Capacitors and SVC

Explanation: Reactive power demand by the HVDC system can be fulfilled by all the mentioned equipment’s.

7. As compared to the HVDC line, the corona and radio interference in a HVAC line are ____
a) more
b) lesser
c) same
d) cannot be determined

Explanation: The corona and radio interference losses are more in ac system.

8. What of the below mentioned statements are incorrect as compared to the HVDC system?
a) Back to back connection is possible
b) More corona losses
c) Distance limitation
d) Extra reactive power compensation

Explanation: Out of all the corona losses are less in HVDC system.

9. It is required to implement the HVDC system using the thyristors in large numbers. Why it becomes necessary to use a large number of thyristor switches?
a) Due to low voltage rating of thyristor switches
b) Due to low current rating of thyristor switches
c) Due to lack of response for open circuit fault
d) Cannot be determined

Explanation: Thyristors have low voltage rating and to achieve high voltage, a series of switches that have to used.

10. The corona loss on a particular system at 50 Hz is 1 kW/phase per km. The corona loss on the same system in case of DC transmission will be ____________
a) Zero
b) 0.5 kW/phase/km
c) 0.33 kW/phase/km
d) 0.6 kW/phase/km

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