Electrical Machines Practice Test 2

1. A three phase induction motor is connected to the infinite bus operating at the normal conditions. There occurs an unbalancing in the supply, leading to _________

unequal heating losses

stopping of motor

increase in lower

none of the mentioned

2. What percentage of the rated output for DC machine and synchronous machine is taken as stray load losses respectively?

0.1% and 5%

1% and 0.5%

0.5% and 1%

3% and 0.1%

3. If one of the phases of the supply breaks down, then the connected three phase induction motor ____________

stops operating after few seconds

continues to run as two phase induction motor

continues to run as single phase induction motor

continues to run as a single phase induction motor, provided load does does not increase beyond 57.7%

4. The effect of short pitched coil on the generated EMF is _____________

either increasing or decreasing

decreasing

increasing

none of the mentioned

5. In a DC generator, the commutator serves as a _________

all of the mentioned

mechanical inverter to invert the direct applied voltage to alternating voltage

none of the mentioned

mechanical rectifier for alternating EMF to direct EMF

6. In an AC machine, the effect of distributing the turns in different slots, results in a further reduction of generated EMF by the factor k_d. This factor is called ____________

coil pitch factor

all of the mentioned

distribution/speed factor

winding factor

7. The equation for slip speed is ____________

ω_r

(ω_r-ω)/ω

(ω-ω_r)/ω

ω-ω_r

8. Which of the following statements are correct regarding brush contact losses?

In synchronous machine: neglected

Any of the mentioned

In DC machine: proportional to armature current

In induction machine: neglected

9. Which of the following statements are correct in a DC machine, when the pole core is usually of smaller cross section than the pole shoe?

(i) smaller cross section requires less copper
(ii) larger pole shoe increases the air gap reluctance
(iii) larger pole shoe increases the flux per pole entering the armature
(iv) larger pole shoe reduces the mechanical strength
(v) larger pole shoe supports the field winding

(ii), (iv), (v)

(i), (ii), (v)

(i), (iii), (v)

(ii), (iii), (v)

10. For a four pole, 16 slot armature with two coil-side/slot having wave connected progressive winding has single turn coils has simplex winding. The number of current paths is?