# Electrical Machine 8

Electrical Engineering MCQ Question Papers: Campus Placement

Subject: Electrical Machine 8

Part 2: List for questions and answers of Electrical Machine II

Q1.In a 20 kVA, 2200 / 220 volts transformer iron and copper losses are 300 and 400 watts respectively. Its efficiency at half load and unity power factor is?

a) 95.11%

b) 96.15%

c) 97.77%

d) 98%

Q2.A 600 kVA transformers have iron losses of 400 kW and copper losses of 500 kW. Its kVA rating for maximum efficiency is given by?

a) 537 kVA

b) 548 kVA

c) 555 kVA

d) 585 kVA

Q3.If the power factor of a transformer increases, then its efficiency will ?

a) Increases

b) Decreases

c) Remains constant

d) Not related to each other

Q4. For maximum efficiency in a transformer?

a) Core losses = 2 * copper losses

b) Core losses = copper losses / 2

c) Core losses = copper losses

d) Core losses = copper losses ? 2

Q5. What happens to the hysteresis losses and eddy current losses, if the frequency of a transformer is increased keeping the supply voltage constant? ?

a) Both will decrease

b) Hysteresis losses will increase and eddy current losses will decrease

c) Hysteresis losses will remain same and eddy current losses will decrease

d) Hysteresis losses will decrease and eddy current losses will remain same

Q6.If the applied voltage is increased by 10% and the applied frequency is increased by 20% of a single phase transformer, the percentage change in eddy current losses will be ?

a) 19%

b) 20%

c) 21%

d) 40%

Q7.In the design of transformer, higher flux density is used. Due to which ?

a) weight per kVA increases

b) weight per kW increases

c) weight per kW decreases

d) weight per kVA decreases

Q8.For a single phase no load transformer, which among the following losses will be minimum??

a) hysteresis losses

b) eddy current losses

c) copper losses

d) mechanical losses

Q9.If the voltage supply of a single phase transformer is doubled and the supply frequency is halved, then the eddy current loss will become ?

a) remains same

b) double of the original

c) four times of original

d) half of the original

Q10.If the supply voltage is kept at constant value and the supply frequency is increased. The magnetizing and core loss component?

a) Both will decrease

b) Magnetizing component will increase and core loss will decrease

c) Magnetizing component will decrease and core loss will increase

d) Both will increase

Q11.If the applied voltage of a certain transformer is increased by 50% keeping the frequency constant, the maximum flux density will become?

a) Remains same

b) 1.5 times the original value

c) Double the original value

d) Half of the original value

Q12. If the power factor of load is near unity and leading, the full load voltage regulation of a power transformer will be ?

a) Zero

b) One

c) 0.5

d) 0.707

Q13.When a resistance is to be transferred from primary to secondary side of transformer with the turns ratio as k, it must be?

a) Multiplied by k ? 2

b) Multiplied by k

c) Divided by k

d) Divided by k ? 2

Q14.For an ideal transformer winding resistances and leakage flux should be ?

a) Least, maximum

b) Both should be maximum

c) Both should be zero

d) Maximum, least

Q15.If V1 is the primary applied voltage and E1 is the primary induced emf. For an ideal transformer?

a) V1 > E1

b) V1 = E1

c) V1 less than E1

d) V1 = E1 / 2

Q16.A transformer is said to be isolation transformer if its primary to secondary ratio is?

a) Equal to one

b) More than one

c) Less than one

d) Equal to 0.5

Q17.If the primary winding is excited by a purely sinusoidal alternating voltage, than the nature of the flux produced is?

a) Square wave

b) Rectangular wave

c) Saw tooth wave

d) Sinusoidal wave

Q18.For the calculation of induced emf in a transformer the flux used in the equation is in its ?

a) RMS value

b) Average value

c) Maximum value

d) Double of its maximum value

Q19.In a transformer tank, grounding is given to protect it from lightening stoke. Grounding lug is usually installed near?

a) Bottom of the tank

b) Top of the tank

c) In the middle of the tank

d) Anywhere on the tank

Q20.The globules of water present in oil may result directly in a breakdown. This can be prevented by?

a) Proper insulation

b) Isolation of oil from air by using an inert gas

c) Heating the tank

d) None of these

Part 2: List for questions and answers of Electrical Machine II