ELECTRICAL MACHINE DESIGN

1. For a soft magnetic material there will be
a) steeply rising magnetization curve.
b) relatively narrow and small hysteresis loop.
c) less energy loss per cycle of magnetization.
d) all the above.


2. Silicon content in iron lamination is kept within 5% as it
a) increases hysteresis loss.
b) increases cost.
c) makes the material brittle.
d) reduces the curie point.
ans: c

3. For under frequency operation the eddy current loss
a) decreases.
b) increases.
c) remains unchanged.
d) cannot be predicted.
ans: a.

4. What is the suitable shape of plunger magnet to give almost flat force-stroke characteristics?
a) Flat faced .
b) Conical.
c) Stepped.
d) Tapered.
ans: d.

5. In a dc machine " contraction coefficient" is used to take into account the reduction of
a) air-gap area due to armature slots.
b) iron losses in the teeth due to lower tooth density.
c) armature mmf due to armature slots.
d) torque due to ventilating duets.
ans: a

6. Carter's coefficient is applicable for estimating
a) requirements of air-gap mmf.
b) flux distribution in air gap.
c) length of air gap.
d) no-load loss.
ans: a

7. A lap wound dc machine has 400 conductors and 8 poles. The voltage induced per conductor is 2 volts. The machine generates a voltage of
a) 100 V
b) 200 V
c) 400 V
d) 800 V
ans: a

8. The yoke of a dc machine
a) must be made of magnetic material.
b) should preferably be made of magnetic material but can be of non-magnetic material.
c) must be made of non-magnetic material.
d) is partially made of magnetic material and partially made of non-magnetic material.
ans: a.

9. The pole shoes of a dc machines
a) are always laminated.
b) are never laminated.
c) are sometimes laminated.
d) are partially laminated.
ans: a

10. Poles of a dc machines are often laminated to
a) reduce pulsation loss.
b) reduce armature reaction.
c) reduce iron weight.
d) dissipate more heat.
ans: a.