# Power systems Objective Type Questions Gate Preparation Power generations-2:

26.The insulation level of 400 kV EHV overhead transmission line us decided on the basis of

a) lightning overvoltage

b) switching overvoltage

c)corona inception voltage

d)radio and TV interference

Answer: switching overvoltage

27.For a 500 Hz frequency excitation, a 50 km long power line will be modelled as

a) short line

b) medium line

c)long line

d)data is not sufficient decision

Answer: long line

28.Bundled conductors are employed to

a) reduce the short circuit current

b) improve system stability

c)decreases system stability

d)increase the short circuit current

Answer: decreases system stability

29.The X: R ratio of 220 kV line as compared to 400 Kev line is

a) greater b) smaller

c)equal d) it could be anything

Answer: smaller

30.If a line is 100% series compensated, it may result into series resonance at power frequency of

a)50 Hz b)100 Hz

c)150 Hz d) none of these

Answer:50 Hz

31.A 60 Hz,320 km lossless line has sending and voltage 1.0 pp. the receiving end voltage on no load is

a)1.1 pp. b)1.088 pp.

c)1.116 pp. d)none of these

Answer:1.088 pp.

32.With 100 % series compensation of lines

a) the circuit is series resonant at power frequency

b) low transient voltage

c)high transient current

d)both (a) and (c)

Answer: both (a) and (c)

33.For certain geometry and operating voltage of the uncompensated transmission line, the ratio of power transfer capability to the surge impedance loading with increase in length

a) increases b) remains unchanged

c)decreases d) uncertain

Answer: decreases

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34.For any fixed degree of inductive shunt compensation, additional series capacitive compensation

a) increases effective length of line

b) increases virtual surge impedance line

c)decreases virtual surge impedance loading of the line

d)none of these

Answer: none of these

35.A loss less line terminated with its surge **impedance** has

a) flat voltage profile

b) transmission line angle is greater than actual length of line

c)transmission line angle is less than actual length

d)both (a) and (b)

Answer: flat voltage profile

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36.Critical voltage limit of a transmission line is increased by

a) increasing the radius of the conductors

b) increasing the spacing between conductors

c)reducing the spacing between conductors

d)reducing the radius of the conductors

Answer: increasing the radius of the conductors

37.The surge **impedance** of 50 miles long underground cable is 50 ohms. For a 25 miles’ length it will be

a)25 ohms b)50 ohms

c)100 ohms d) none of these

Answer:50 ohms

38.For reducing tower footing **resistance**, it is better to use

a) chemical and ground rods only

b) chemical and counterpoise only

c)ground rod and counterpoise only

d)chemical, ground rods and counterpoise

Answer: ground rod and counterpoise only

39.An RLC series circuit remains predominantly inductive

a) at resonance frequency

b) below resonance frequency

c)above resonance frequency

d)at lower half power frequency

Answer: above resonance frequency

40.If ? is the loss angle of the cable, then its power factor is

a) sin ?

b) cos ?

c)independent of ?

d)depends upon ? but it is not as per (a) and (b)

Answer: sin ?

41.For the same voltage boost, the reactive power capacity is

a) more for shunt capacitor

b) more for series capacitor

c)it is same for both series and shunt

d)uncertain

Answer: more for shunt capacitor

42.A power station consists of two synchronous generators A and B of rating 250 MVA and 500 MVA with inertia 1.6 p.u.and 1 p.u. respectively on their own base MVA ratings. The equivalent P.U intertie for the system on 100 MVA common base will be

a)2.6

b)0.615

c)1.625

d)9.0

Answer:9.0

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43.The per unit impedance of a circuit element is 0.15. if the base kV and base MVA are halved, then the new value of the per unit impedance of the circuit element will be

a)0.075 b)0.15

c)0.30 d)0.600

Answer:0.30

44.A 66 kV system has string insulator having five discs and the earth to disc capacitance ratio at 0.10.the string efficiency will be

a)89% b)75%

c)67% d)55%

Answer:67%

45.The main criterion for selection of the size of a distribution for a radial distribution system is

a) voltage drop b) corona loss

c)temperature rise d) capital cost

Answer: voltage drop

46.If an induction machine is run at above synchronous speed, it acts as

a) a synchronous motor

b) an induction generator

c)an inductor motor

d)none of these

Answer: an induction generator

47.The low voltage windings of a 400/230 V,1-phase,50Hz transformer is to be connected to a 25Hz, the supply voltage should be

a)230V b)460V

c)115V d)65V

Answer:115V

48.The order of the sub-harmonic during SSR for 50 Hz normal frequency is

a)25 Hz b)16 2/3 Hz

c)10 Hz d) none of these

Answer: none of these

49.Whenever the conductors are dead-ended of there is a change in the direction of the transmission line, the insulators used are of the

a) pin type b) suspension type

c)strain type d) shackle type

Answer: strain type

50.The time taken for a surge to travel a 600 km long overhead transmission line is

a)6s b)1s

c)0.02s d)0.002s

Answer:0.002s