High voltage direct current (HVDC) and High voltage engineering(HVE) MCQs Part-7

HVDC/HVE 

1. If pulse number is = p and k is an integer, the voltage harmonic generated on the AC side is_____.

(a) pk

(b) 2pk

(c) pk ± 1

(d) 2pk ± 1

2. In a 12-pulse converter, the phase difference between the two 6-pulse bridges is________.

(a) 0°

(b) 60° 

(c) 30°

(d) 15°

3. The lowest current harmonic produced in 12-pulse converters is________.

(a) 11

(b) 13

(c) 23

(d) 25

4. 8. Increase in pulse number has the effect of_________.

(a) increasing harmonics

(b) decreasing the harmonic number 

(c) increasing the lowest harmonic number

(d) no effect

5. Effect of increasing overlap angle is to________. 

(a) decrease amplitude of harmonic voltage

(b) increase the amplitude of harmonic voltage

(c) no effect on magnitude

(d) depends on the relative values of a

6. With CC or CIA control, as overlap angle m increases, the amplitude of harmonic current_____.

(a) increases

(b) no effect

(c) decreases for some harmonics and increases for some harmonics 

(d) decreases

7. Filters used in 12-pulse converters usually on the AC side are_________.

(a) 5th, 7th and high-pass 

(b) 11th, 13th and high-pass

(c) 6th, 12th and high-pass

(d) Only high-pass filter

8. For power frequency, the harmonic filter acts as a______. 

(a) leading p.f. load supplying leading kVA

(b) lagging p.f. load supplying lagging kVA

(c) (a) or (b) depending on the p.f. of the system

(d) leading p.f. at rectifier end and lagging p.f. at inverter end

9. The maximum value of the harmonic current depends on____.

(a) firing angle

(b) overlap angle

(c) DC current 

(d) both firing angle and overlap angle

10. TIF factor usually lies between_______.

(a) 10 to 25

(b) 20 to 30 

(c) 25 to 50

(d) 50 to 100

11. DSS product defined for harmonic distortion is given by_______.

(a)1/222()mn nnI F=È ˘ ÂÎ ˚

(b)1/222( )mn nnI F=È ˘Í ˙ Î ˚ Â

(c)1/22( )mn n nnI Z F=È ˘Í ˙ Î ˚  

(d)1/2221( )100mn nnI ZE=È ˘Í ˙ Î ˚ ¥ÂIn

12. Network impedance characteristic is given as_______. 

(a) Locus of Z in R, X plane for each harmonic

(b) Network impedance in R, X plane for a given harmonic

(c) Variation of harmonic current with the magnitude of harmonic voltage

(d) All of the above

13. Harmonic filters are protected by________.

(a) overcurrent relays 

(b) lightning arrestors

(c) spark gaps

(d) none of the above

14. In HVDC-VSC schemes, filters are used________.

(a) only on the AC side

(b) only on the DC side

(c) both AC and DC side

(d) no filter is needed

15. Size of an AC filter and its MVAR capacity is much less in VSC schemes, as_______.

(a) no harmonics are generated

(b) harmonics generated are of much higher order 

(c) filter need not supply RKVA at power frequency and harmonics generated are at switching frequency and higher

(d) none of the above

16. In a 2nd order or 3rd order filter, which of the components R, L or C are to be rated to full AC power frequency voltage?

(a) Inductor 

(b) Capacitors

(c) Resistors

(d) Both inductors and capacitors

17. Advantage of ground return in HV-bipolar DC system is____

(a) less power loss

(b) can be built in stages

(c) in the event of fault, 50% power is available 

(d) all of the above

(e) none of the above

18. The ground currents in HVDC system fl ow through_________.

(a) small area

(b) small area along the line 

(c) very large area and does not confine to route of the line

(d) very large area along the route of the line

19. The order of ground currents and polarity in bipolar system is________.

(a) 1 to 3% either polarity

(b) 1 to 3% negative polarity

(c) 1 to 3% positive polarity

(d) 5 to 10% either polarity

20. The resistivity of average land surface is of the order (W-m)______.

(a) 1 to 1000 

(b) 50 to 200

(c) 1000

(d) 1000–10,000