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Electrical Machine MCQ | practical training (Machine and protection MCQ)

1. Partial breakdown of winding insulation or due to overload on the supply system, this common problem known as ----- 
  • a. None of these 
  • b. Overspeed 
  • c. Overcurrent 
  • d. Fallure of the prime-mover 
  • e. Failure of the field 
Ans: c (Overcurrent) 


2. Which tests are to be conducted to draw circuit diagram for a given induction motor? ((I. No Load test, II. Blocked rotor test, III. Running test, IV. Voltmeter-Ammeter test)) 
  • a. I, II, III 
  • b. I, II, IV 
  • C. I, II 
  • d. I, II, III, IV 
Ans: I, II(no load test and Blocked rotor test) 


3. The magnitude of the unprotected zone of the generator stator winding depends upon the value of earthing resistance and relay setting. Select one: 
  • a.True 
  • b.False 
Ans: True 


4. At starting, developed mechanical torque is and developed power is 
  • a. not zero, zero 
  • b. zero, not zero 
  • c. not zero, maximum 
  • d. zero, zero 
Ans : a (not zero, zero) 


5. At starting, developed mechanical power is……. and developed torque is…… 
  • a) zero, not zero 
  • b) zero, zero 
  • c) not zero, zero 
  • d) not zero, maximum 
Ans: a(zero, notZero) 


6. Three phase voltages are applied to the three windings of an electrical machine. If all supply terminal reversed, then the RMF wave...... 
  • a. Direction remains same, amplitude unaltered 
  • b. Direction remains same, amplitude alters 
  • c. Direction reverses, amplitude alters 
  • d. Direction reverses, amplitude unaltered 
Ans: a ( Direction remains same, amplitude unaltered) 


7. If the stator winding fault is cleared quickly, it may lead to-------- 
  • a.minimize the extent of damage. 
  • b.burning and welding-up of stator laminations. 
  • c.burning of stator coils. d. None of these. 
Ans : a(minimize the extent of damage) 


8. The field of each individual phase in rotating machines is 
  • a. None of the mentioned. 
  •  b. a rotating magnetic filed RMF. 
  • c. not a rotating RMF but its amplitude pulsates. 
  • d. not a rotating RMF and its amplitude doesn't alternate. 
Ans: c (not a rotating RMF but its amplitude pulsates.) 


9. A 10kW,400V, 4-pole star connected induction motor gave the following test results: (( No load test: 400V, 8A, 250 W - Blocked rotor test: 90V,35A,1350 W)); The dc resistance is 0.6 ohms. The stator resistance is 
  • a. 0.6 ohms 
  • b. 0.9 ohms 
  • c. 1.2 ohms 
  • d. 0.4 ohms . 
  • e. 0.3 ohms 
Ans: e (0.3 ohm) 

10. If the stator winding fault is not cleared quickly, it may lead to 
  • (i) burning of stator coils 
  • (ii) burning and welding-up of stator laminations 
  • (iii) damage to other equipment 
  • (iv) all above 
Ans: iv(all above) 


11. The actual rotor resistance referred to the stator if the induction motor is 
  • a (r2)/s 
  • b. (r2)/(1-5) 
  • c (r2) (1-s)/s 
  • d. r2 
Ans :d (r2) 


12. The speed of RMF when a single phase supply is connected to the stator of three phase induction motor is 
  • a. -Ns 
  • b. zero 
  • c. 2NS 
  • d. Ns 
Ans : b(zero) 


13. The direction of rmf when a three phase supply is given to stator of three phase induction motor is? 
  • a) Zero 
  • b) Ns 
  • c) 2Ns 
  • d) –Ns 
Ans : b(Ns) 


14. The making/breaking circuit provides a command causing the appropriate circuit-breaker to disconnect. Select one: 
a.True 
b.False 
Ans: TRUE 


15. Unbalanced loading arises when a fault is ............ 
  • I. Faults between phases and ground 
  • ii. None of these 
  • iii. Faults between phases 
  • iv. Faults to earth 
  • v. All of these 
  • vi. Three-phase faults 
Ans : iii and iv ( Faults between phases and Faults to earth) 


16. During no load test the wattmeter reading will be: ((I. stator copper loss, II. stator core loss, I rotor core loss , IV. friction and windage losses, V. Rotor copper loss )) 
  • a. ll, lll 
  • b. XI, IV 
  • C. I, II 
  • D. I, II, III 
Ans: b(XI, IV) 


17. The 3-phase IM is start and run as 
  • A. stat connected. 
  • B. delta connected 
  • C. delta then star respectively. 
  • D. star then delta respectively 
Ans : D(star then delta) 


18. The consequences of a sudden loss of all or the major part of the load on the alternator ......
  • i. Failure of the prime-mover
  • ii. Overspeed 
  • iii. Overcurrent 
  • iv. None of these 
  • V. Failure of the field 
Ans : II (Overspeed) 


19. star-commerte, 3-phase, OMVA, EG KV alternator has a perphase reactance of 10%. It is protected by Merz-Price a circulating-current principle that is set to operite for fault currents not less than 105 A. The value of carthing resistance to be provided in order to ensure that only 10% of the alternator winding remains unprotected is 
  • A. 2.171 ohm 
  • B. 2.159 ohm 
  • C. 2.059 ohm 
  • D. 2.176 ohm 
  • E. None of the above. 
Ans : C( 2.059 ohm) 


20. Three phase voltages are applied to the three windings of an electrical machine. If all supply terminals are reversed, then the RMF wave...... 
  • a. Direction remains same, amplitude unaltered 
  • b. Direction remains same, amplitude alters 
  • c. Direction reverses, amplitude alters 
  • d. Direction reverses, amplitude unaltered 
Ans : a (Direction remains same, amplitude unaltered) 


21. A star-connected, 3-phase, 8MVA, 6.6 kV alternator has a per-phase reactance of 10%. It is protected by Merz-Price a circulating-current principle that is set to operate for fault currents not less than 195 A. The value of earthing resistance to be provided in order to ensure that only 10% of the alternator winding remains unprotected is ....... 
Ans : (1.9533 ohm


22. External resistors method of induction motor starting, It cause 
  • a. Reduce motor terminal voltage 
  • b. Reduced efficiency 
  • C.all of the mentioned 
  • d. Reduce the current 
Ans : c(all of the mentioned) 


23. Full voltage starting of induction motor may cause
  • a. dip in the voltages 
  • b. high voltage. 
  • c. high losses 
  • d. all of the mentioned 
Ans : a(dip in the voltage) 


24. The alternator runs as a synchronous motor and draws current from the supply system, These consequences are described as 
  • A. Failure of the prime-mover 
  • B. None of these 
  • C. Failure of the field 
  • D. Overcurrent 
Ans : a( Failure of the prime-mover) 


25. At standstill the equivalent of the 3-phase induction motor is similar to ___ 
  • a) short-circuited two winding transformer. 
  • b) open circuit two winding transformer. 
  • c) stand still synchronous motor. 
  • d) none of the mentioned. 
Ans : a(short-circuited two winding transformer) 


26. Field failure of alternators needs to automatic protection against this contingency. Select one: 
  • a.True 
  • b.False 
Ans : False 


27. If the phase sequence of supply currents are reversed, then the direction of rotation of the 3 Phase IM wave will 
  • a. None of the mentioned 
  • b. Remains unchanged 
  • C. Cannot be determined 
  • d. Be reversed 
Ans: d(Be reversed) 


28. Overvoltage in an alternator occurs when speed of the primemover decreases due to sudden loss of the alternator load. Select one: 
  • a.True 
  • b.False 
Ans : False 


29. In the Merz-Price circulating scheme, the secondaries of each set of current transformers are connected in delta. Select one: 
  • a.True 
  • b.False 
Ans : False 


30) (I) Even at no load, a large 3-Ph IM must be started at reduced voltage. (11) If a large 3-Ph IM is started quickly at full voltage, it will be damaged. Is both statements (1), and (II) are false? Select one: 
  • A.True 
  • B.False 
Ans: False 


31) We do not require any protection against prime mover failure in case of 
  • A. Turbo generator sets 
  • B. Hydro generator sets 
  • C. Diesel engine driven alternators 
  • D. Back pressure turbo generators 
Ans : a(Turbo generator sets) 


32 ) Advantage of hydro-electric power station is Select one: 
  • a. Low operating cost 
  • b. Free from pollution problems 
  • c. No fuel transportation problems 
  • d. All of the above. 
Ans: d (All of the above) 


33) Short-circuit currents are due to…….. 
  • A. single phase to ground faults 
  • B. phase to phase faults 
  • C. two phase to ground faults 
  • D. three phase faults 
  • E. any of these 
Ans: E (any of these)


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Electrical Machine MCQ | practical training (Machine and protection MCQ)

A 10kW,400V, 4-pole star connected induction motor gave the following test results: (( No-load test: 400V, 8A, 250 W -- Blocked rotor test: 90V,35A,1350 W )) ; The dc resistance is 0.6 ohms. The stator resistance is
  • a. 1.2 ohms
  • b. 0.4 ohms
  • c. 0.6 ohms
  • d. 0.9 ohms
  • e. 0.3 ohms

The consequences of a sudden loss of all or the major part of the load on the alternator -----------
  • i. Failure of the prime-mover
  • ii. Failure of the field
  • iii. None of these
  • iv. Overspeed
  • v. Overcurrent

The actual rotor resistance referred to the stator if the induction motor is 
  • a. (r2)*(1-s)/s 
  • b. r2 
  • c. (r2)/s 
  • d. (r2)/(1-s)

The field of each individual phase in rotating machines is ...... 
  • a. not a rotating RMF but its amplitude pulsates 
  • b. a rotating magnetic filed RMF 
  • c. None of the mentioned 
  • d. not a rotating RMF and its amplitude doesn’t alternate

If the phase sequence of supply currents are reversed, then the direction of rotation of the resultant MMF wave will ___________
  • a) Be reversed
  • b) Remains unchanged
  • c) Cannot be determined
  • d) None of the mentioned

When the rotor of a 3-phase induction motor is blocked, the slip is ……..
  • zero
  • 0.5
  • 0.1
  • 1
Partial breakdown of winding insulation or due to overload on the supply system, this common problem known as ------------- 
  • i. Failure of the field 
  • ii. Overcurrent 
  • iii. Failure of the prime-mover 
  • iv. None of these 
  • v. Overspeed

At no-load, the rotor core loss of a 3-phase induction motor is ………
  • large
  • small
  • practically zero
  • none of the above

A star-connected, 3-phase, 10 MVA, 6.2 kV alternator is protected by circulating current protection, the star point being earthed via a resistance (r). If 80% of the stator winding is protected against earth faults. Assume an earth fault setting of 15% of full-load current, and neglect the impedance of the alternator winding. Then the value of the earthing resistor is ----------- Ω 
  • i. 3.844 
  • ii. 5.125 
  • iii. 2.175 
  • iv. None of these 
  • v. 4.355

As a 3-phase induction motor, as load decreases from full load to half load, A. pf improves B. torque decreases C. slip decreases D. speed increases 
  • i. D only 
  • ii. B, C, D 
  • iii. A, B, D 
  • iv. A, B, C, D 
  • v. A only

If the neutral point of a star-connected the alternator is earthed through a low resistance, protection schemes will not provide sufficient sensitivity for earth-faults. Select one: 
  • True 
  • False


3-phase, 10 MVA, 6.0 kV alternator is protected by Merz Price circulating-current principle if the minimum fault current is 120A. The E.M.F induced in x% winding is (33.641x) volts. Select one: 
  • True 
  • False
answer (false) and the correct phrase is 
3-phase, 10 MVA, 6.0 kV alternator is protected by Merz Price circulating-current principle if the minimum fault current is 120A. The E.M.F induced in x% winding is (34.641x) volts.


For 3-phase induction motor, the characteristic of motor the torque _______ with respect to slip. 
  • a. increases then decrease 
  • b. decreases 
  • c. remains constant 
  • d. increases 
  • e. decreases then increase
answer is (a)increses then decrease because its exponnetial
 
For 3-phase induction motor, the characteristic of motor the torque _______ with respect to slip.  a. increases then decrease  b. decreases  c. remains constant  d. increases  e. decreases then increase answer is (a)increses then decrease because its exponnetial

Starting methods not applicable to both squirrel-cage and slip ring induction motors is/are: (( I. DOL starting , II. Auto transformer starting , III. Rotor resistance starting , IV. Stator resistance starting )) 
  • a. III 
  • b. I, II, III 
  • c. I, II, IV 
  • d. I, II

If the phase sequence of supply currents are reversed, then the direction of rotation of the 3-Phase IM wave will 
  • a. Cannot be determined 
  • b. Remains unchanged 
  • c. None of the mentioned 
  • d. Be reversed

If the three phase induction motor connected to a power grid with 3-star connected capacitors draws a real positive power (P) and zero reactive power (Q). If the capacitors is reconnected to run with delta-capacitors , then the motor will draw .............. (P) and ................. (Q). 
  • a. positive, negative 
  • b. positive, positive 
  • c. negative, negative 
  • d. negative, positive

Overvoltage in an alternator occurs when speed of the prime-mover decreases due to sudden loss of the alternator load. Select one: 
  • True 
  • False
answer is ( false ) and the correct is  
Overvoltage in an alternator occurs when speed of the prime-mover increase due to sudden loss of the alternator load


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