Switchgear and Protection MCQ

Test your knowledge with important Switchgear and Protection MCQ and their applications. These MCQs are beneficial for competitive exams too. Explore 30 + more Switchgear and Protection MCQs at Bissoy

• A lossless TL having SIL of 3000 MW is provided with uniform distributed series capacitance compensation of 25% and shunt compensation of 30% then the compensated impedance of TL will be(in pu) ____________
  ক

  0.7595

  খ

  2.88

  গ

  0.647

  ঘ

  3.27
• A lossless TL having SIL of 3000 MW is provided with uniform distributed series capacitance compensation of 25% and shunt compensation of 30% then the SIL of compensated TL will be _______________
  ক

  3949.9

  খ

  3289

  গ

  2784.9

  ঘ

  2877.6
• For a 100 MVA, 11 kV three phase Alternator observes a three phase fault at terminals of it. If the fault current is 2000 A, the pu value of positive sequence reactance ______
  ক

  2.62

  খ

  0.46

  গ

  1.31

  ঘ

  0.92
• The inertia constant of two groups of machines which do not swing together are 4 and 20 MJ/MVA, the equivalent inertia constant of the system is _________
  ক

  2.85

  খ

  14

  গ

  6

  ঘ

  12
• The below mentioned graph is a recorded data of the voltage fluctuation of the network, then it can be concluded that these faults are __________
  ক

  L-G

  খ

  A three phase motor short

  গ

  Feeder fault

  ঘ

  Any of the mentioned
• If short TL is delivering a lagging power factor load, sending end p.f. would be ________
  ক

  (VrcosФr+IR)/Vs

  খ

  (VrcosФr+IRsinФr)/Vs

  গ

  (VrsinФr+IR)/Vs

  ঘ

  (VssinФr+IRcosФr)/Vs
• An isolated generator connected to a turbine with its continuous maximum power of 20 MW, 50 Hz. Generator connected with two loads of 8 MW, each operate at 50 Hz.. Generator has 5% droop characteristic. If an additional load of 6 MW is added then frequency will be ___________
  ক

  50.25

  খ

  40.75

  গ

  49.75

  ঘ

  48.75
• A single phase TL has copper conductor of 0.775 cm2 cross section through which 200 kW at UPF at 330 V is to be maintained. If the efficiency of transmission line is 90%, then the minimum length of TL is _________(in km and take specific resistance to be 1.785 μΩ/cm).
  ক

  13.6 km

  খ

  14 km

  গ

  136 km

  ঘ

  16.4 km
• A 50 Hz four pole turbo-generator rated 100 MVA, 11 kV has an inertia constant of 8 MJ/MVA. If the mechanical input is suddenly raised to 80 MW for an electrical load of 50MW, then the rotor acceleration is __________
  ক

  337.5

  খ

  3.375

  গ

  457.5

  ঘ

  4.57
• A 100 MVA synchronous generator operates on full load at a frequency of 50 Hz. The load is suddenly reduced to 50 MW. Due to time lag in governor system, the steam valve begins to close after 0.4s. The change in the frequency (H=5 kW-s/KVA) is ___________
  ক

  1

  খ

  0.5

  গ

  -1.5

  ঘ

  0.8
• A 275 kV TL has following line constants A=0.85ʟ5o, B=200ʟ75o. The active power angle such that the voltage to be maintained at the other end will be 275 kV ______________
  ক

  22

  খ

  16

  গ

  18

  ঘ

  24
• A 275 kV TL has following line constants A=0.85ʟ5o, B=200ʟ75o. The active power received if the voltage to be maintained is 275kV will be ______________
  ক

  117.63

  খ

  220

  গ

  120

  ঘ

  115.25
• A single phase motor is connected to 400V, 50Hz supply. The motor draws a current of 31.7A at a power factor 0.7 lag. The capacitance required in parallel with motor to raise the power factor of 0.9 lag (in micro farads) is ___________
  ক

  94.62

  খ

  282.81

  গ

  108.24

  ঘ

  46.87
• A single phase distributor of 1 km long has resistance and reactance per conductor of 0.1Ω and 0.15 Ω respectively. If the far end voltage Vb=200V and current is at 100A at 0.8 lag. At the midpoint a current of 100A is tapped at a pf of 0.6 pf with ref to voltage Vm at mid point. The voltage magnitude at M is __________
  ক

  218V

  খ

  200V

  গ

  232V

  ঘ

  220V
• A power system network is connected as shown in the figure below. Sd1=15+j5 pu Sd2=25+j15 pu Zcable = j0.05pu |V1|=|V2|=1 pu. The torque angle for the system will be _______
  ক

  14.4

  খ

  22.1

  গ

  16.2

  ঘ

  18.2
• Unbalancing of an alternator may occur due to ____________
  ক

  single phase fault

  খ

  unbalanced loading

  গ

  line breaking

  ঘ

  all of the mentioned
• Bias is used in the relay protection to _______________
  ক

  provide balanced sharing of current

  খ

  reduce current level

  গ

  deivert the current

  ঘ

  none of the mentioned
• A longitudinal differential protection on stator can detect inter-turn on the stator.
  ক

  True

  খ

  False
• 4.If the specified fault setting for a winding is mentioned as 20%, then what can be inferred about it?
  ক

  If a terminal fault has its current limited to the full load rating, then 20% of winding from neutral end will be unprotected

  খ

  If a terminal fault has its current limited to the full load rating, then 80% of winding from neutral end will carry current

  গ

  If a terminal fault has its voltage limited to the full load rating, then 20% of winding from neutral end will be unprotected

  ঘ

  Any of the mentioned
• We need the biasing of differential relay biased to avoid mal operation when used for transformer protection due to ____________
  ক

  mismatch of CT

  খ

  saturation of

  গ

  difference in connection of both sides of CT

  ঘ

  current setting mismatch
• The given figure shows protection system scheme for one phase of generator. A high resistance fault occurs near the neutral end with the current distribution as marked. The slope of the relay is 10% and pick-up current of 0.15A. The CT ratio is 500/5. Will the relay operate under given circumstances?
  ক

  True

  খ

  False
• The frequency of the carrier in the case of carrier-current-pilot scheme is in the range of _________
  ক

  50 kHz-500 kHz

  খ

  1 kHz-10 kHz

  গ

  25 kHz-50 kHz

  ঘ

  15 kHz-25kHz
• If a transformer is provided with differentially connected relay. To prevent the mal operation of the relay, the relay restraining coil is biased with ______________
  ক

  3rd harmonic

  খ

  2nd harmonic

  গ

  7th harmonic

  ঘ

  5th harmonic
• If a transformer is provided with differentially connected relay. To prevent the mal operation of the relay, the relay relay operating coil is biased with ______
  ক

  3rd harmonic

  খ

  2nd harmonic

  গ

  7th harmonic

  ঘ

  5th harmonic
• While a transformer is energised, the differentially connected relay will
  ক

  mal operate

  খ

  not mal operate

  গ

  mal operate for lagging loads

  ঘ

  never mal operate
• The neutral of the three phase 20 MVA, 11kV alternator is earthed through a resistance of 5 ohms, the relay is set to operate when there is an out of balance current of 1.5 A. The CTs have a ratio of 100/5. What should be the minimum value of the earthing resistance to protect 90% of winding?
  ক

  2.12 Ω

  খ

  1.12 Ω

  গ

  4.24 Ω

  ঘ

  3.24 Ω
• The neutral of the three phase 20 MVA, 11kV alternator is earthed through a resistance of 5 ohms, the relay is set to operate when there is an out of balance current of 1.5 A. The CTs have a ratio of 100/5. What percentage of the winding is protected against earth faults?
  ক

  76.4

  খ

  77.8

  গ

  73

  ঘ

  None of the mentioned
• The neutral of the three phase 20 MVA, 11kV alternator is earthed through a resistance of 5 ohms, the relay is set to operate when there is an out of balance current of 1.5 A. The CTs have a ratio of 100/5. What percentage of the winding is protected against L-G faults?
  ক

  76.4

  খ

  77.8

  গ

  73

  ঘ

  None of the mentioned
• A three phase transformer having a line voltage ratio of 400/33000 V is connected in the star-delta. The CTs on the 400V side have a CT ratio of 1000/5. What will be the current through the pilot wire?
  ক

  5√3 A

  খ

  5/√3 A

  গ

  5 A

  ঘ

  1/5 A
• A three phase transformer having a line voltage ratio of 400/33000 V is connected in the star-delta. The CTs on the 400V side have a CT ratio of 1000/5. What must be the ratio of CTs on the 33000 side?
  ক

  7/5

  খ

  5/7

  গ

  3/5

  ঘ

  5/2