# Electrical Machine 7

Electrical Engineering MCQ Question Papers: Campus Placement

Subject: Electrical Machine 7

Part 1: List for questions and answers of Electrical Machine II

Q1. In pole amplitude modulation method for controlling number of poles, practically, the wave used for modulation is?

a) Square wave

b) Triangular wave

c) Saw tooth wave

d) Sinusoidal wave

Q2. The best suited method for smooth speed control by controlling number of poles is ?

a) Consequent poles method

b) Multiple stator winding method

c) Pole amplitude modulation method

d) None of these

Q3.The consequent pole method used for controlling the number of poles can be used for ?

a) Only squirrel cage type motors

b) Only slip ring induction motor

c) For both squirrel cage and slip ring induction motor

d) None of these

Q4.The method which can be used for the speed control of induction motor from stator side is?

a) V / f control

b) Controlling number of stator poles to control Ns

c) Adding rheostats in stator circuit

d) All of these

Q5. In textile machines, to avoid breaking of threads, soft starters are used. The commonly used method in soft starter is?

Direct online method

a) Star-delta method

b) Thyristor voltage controller method

c) Thyristor current controller method

Q6. A 3 phase induction motor in a short circuit current is equal 3 times of the full load current. If the full load slip is 2%, then the starting torque as a percentage of full load torque is ?

a) 6% of full load torque

b) 18% of full load torque

c) 36% of full load torque

d) None of these

Q7. For parallel operation of transformers, the p.u. impedances of transformer must be (based on their own kVA rating) ?

a) directly proportional to their ratings

b) inversely proportional to their ratings

c) equal

d) none of these

Q8.For satisfactory parallel operation, the circulating current should not exceed ? 5% of normal rated current

a) 50% of normal rated current

b) 10% of normal rated current

c) 25% of normal rated current

Q9.If the transformers have different kVA ratings, then for parallel operation the equivalent impedances should be?

a) Directly proportional to individual kVA rating

b) Inversely proportional to individual kVA rating

c) Inversely proportional to the square of the individual kVA rating

d) Directly proportional to the square of individual kVA rating

Q10.For carrying out parallel operation, transformers should have same X / R ratio in order to avoid ?

a) Leakage reactance

b) Insulation failure

c) Circulating current

d) Inrush current

Q11.Two transformers are operated in parallel, most essential condition to be satisfied is ?

a) Polarities should be same

b) Leakage reactance should be equal

c) Turns ratios should be equal

d) Impedances should be in proportion to their kVA rating

Q12.For parallel operation of transformers, the most satisfactory condition is achieved when the load shared by the transformers is in exact proportion with their?

a) Efficiency

b) Ratings

c) Impedances

d) None of these

Q13.While performing sumpner’s test on transformer, if the secondary are not in series opposition then the meter will read ?

a) 0

b) Twice of the induced emf in each secondary’s

c) Equal to the induced emf in each secondary’s

d) Keep fluctuating

Q14.In sumpner’s test, the net voltage in the local circuit of secondary’s is ?

a) Equal to zero

b) Twice of the induced emf in each secondary’s

c) Equal to the induced emf in each secondary’s

d) Square of the induced emf in each secondary’s

Q15. While conducting the sumpner’s test, the primaries of the two identical transformers are connected in parallel across the supply. The secondary’s are connected in?

a) Parallel

b) Series opposition

c) Both in series and parallel

d) Not connected at all

Q16.Which test is also called as back to back test??

a) Retardation test

b) Sumpner’s test

c) Field test

d) Voltage drop test

Q17. If short circuit test is performed on the transformer with constant rated voltage and increased frequency, then the short circuit current and power factor ?

a) Both will increase

b) Both will decrease

c) Increase, decrease

d) Decrease, remains constant

Q18. If the transformer is step – up transformer then for performing short circuit test meter is connected to the ?

a) H.V. side

b) L.V. side

c) Any side

d) Test cannot be performed on step up t / f

Q19.Open circuit test is to be performed on transformer to find ?

a) Constant losses

b) Copper losses

c) Both (a) and (b)

d) None of these

Q20.A 500 kVA single phase transformer has 90% efficiency at both half load and full load at unity power factor. Then iron losses will be?

a) 12.55 KW

b) 13.55 kW

c) 16.55 kW

d) 18.55 KW

Part 1: List for questions and answers of Electrical Machine II