# Electrical Machine 3

Electrical Engineering MCQ Question Papers: Campus Placement

Subject: Electrical Machine 3

Part 3: List for questions and answers of Electrical Machine I

Q1.For the star-star connection of three phase transformer, the phase angle between the phase voltages and line voltages on both primary and secondary side is

a) 0 degree

b) 30 degree

c) 60 degree

d) 120 degree

Q2.While connecting three phase transformer in star-star connection, the terminals of secondary is wrongly joined. Then the mutual phase angle and magnitude of line to line voltages of secondary will

a) Equal to 120 degree and equal as before

b) Not equal to 120 degree and different

c) Equal to 120 degree and different

d) None of these

Q3. For the parallel operation of three phase transformers, which among the following connection is not applicable?

a) Δ  – Δ  to Y – Y

b) Y – Δ  to ? – Y

c) Y – Y to Y – Y

d) None of these

Q4.Due to presence of third harmonic component in the star-star connection of three phase transformer, the frequency of the circuit component becomes

a) Three times of the circuit frequency

b) One third of the circuit frequency

c) Remains same

d) None of these

Q5.In star-star connection of three phase transformer, if VL is the line voltage and IL is the line current then phase voltage and phase current is given by

a) VL / root 3 , IL

b) VL , IL

c) root 3VL , IL /root 3

d) VL, IL / root 3

Q6.The phase shift in a star-star connected three phase transformer is

a) 0 degree

b) 30 degree

c) 60 degree

d) 120 degree

Q7.If K is the transformation ratio, then the secondary phase voltage of delta-delta connected three phase transformer will be

a) 1/K times of the primary phase voltage

b) Equal to the primary phase voltage

c) 1/K ? 2 times of the primary phase voltage

d) K times the primary phase voltage

Q8.For large low voltage transformers, the most commonly connections used are

a) Star- star connection

b) Delta-delta connection

c) V connection

d) All of these

Q9.In case of delta-star connection of three phase transformer, secondary line voltage with respect of primary line voltage is at

a) 0 degree

c) 30 degree lagging

d) 60 degree lagging

Q10.The most commonly used connections for power systems as a step-up and step-dow transformers are

a) Star-delta, star-star

b) Delta-star, star-delta

c) Star-star, delta-delta

d) Star-delta, delta-star

Q11.The load carried by V – V connection is

a) 47.7% of the original load

b) 57.7% of the original load

c) 67.7% of the original load

d) 87.7% of the original load

Q12. Consider three transformers connected in delta-delta fashion and supplying their rated load. Now if one of the transformer is removed then each of the remaining two transformer is overloaded. The overload on each transformer is given as

a) 1

b) 1.232

c) 1.732

d) 1.872

Q13.The average power factor at which V-V bank is operating is less than that with the load. The power factor is

a) 57.7% of the balanced load power factor

b) 66.7% of the balanced load power factor

c) 86.6% of the balanced load power factor

d) None of theses

Q14.With a bank of two single phase transformers connected in V – V fashion supplying a balanced three phase load with Cos f as power factor. The power factor of the two transformers is given by

a) Cos f , Cos f

b) Cos f, Cos(30+ f)

c) Cos(30- f), Cos(30+ f)

d) Cos(30- f), Cos f

Q15.In T-T connection, the percentage tapping of main transformer and teaser transformer are

a) 50%, 86.6%

b) 50%, 50%

c) 86.6%, 86.6%

d) 86.6%, 50%

Q16.In T-T connection, the ratio of actual capacity to the available capacity is

a) 1

b) 0.928

c) 1.928

d) 0.5

Q17.Due to overdamping, the instrument will become

a) Slow

b) Lethargic

c) Fast

d) Both (a) and (b)

Q18.Scott connection is used for the conversion of

a) Single phase to three phase

b) Three phase to single phase

c) Single phase to two phase

d) All of these

Q19.In Scott connection, the voltage across the teaser leads the mains by

a) 30 degree

b) 60 degree

c) 90 degree

d) 120 degree

Q20.In a single phase, full wave bridge circuit and in three phase, delta full wave bridge circuit, the ripple voltage frequency is always

a) Twice the line frequency, six times the line frequency

b) Both will be twice the line frequency

c) Both will be six times the lines frequency

d) None of these

Part 3: List for questions and answers of Electrical Machine I