McqMate
Chapters
| 101. |
The condition for maximum efficiency for a D.C. generator is |
| A. | eddy current losses = stray losses |
| B. | hysteresis losses = eddy current losses |
| C. | copper losses = 0 |
| D. | variable losses = constant losses |
| Answer» D. variable losses = constant losses | |
| 102. |
D.C. generators are normally designed for maximum efficiency around |
| A. | full-load |
| B. | rated r.p.m. |
| C. | rated voltage |
| D. | all of the above |
| Answer» A. full-load | |
| 103. |
In a D.C. generator, the iron losses mainly take place in |
| A. | yoke |
| B. | commutator |
| C. | armature conductors |
| D. | armature rotor |
| Answer» D. armature rotor | |
| 104. |
D.C. generators are installed near the load centres to reduce |
| A. | iron losses |
| B. | line losses |
| C. | sparking |
| D. | corona losses |
| Answer» B. line losses | |
| 105. |
The purpose of retardation test on D.C. shunt machines is to find out |
| A. | stray losses |
| B. | eddy current losses |
| C. | field copper losses |
| D. | windage losses |
| Answer» A. stray losses | |
| 106. |
Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ? |
| A. | Swinburne'stest |
| B. | Hopkinson'stest |
| C. | Field test |
| D. | Brake test |
| Answer» C. Field test | |
| 107. |
Hopkinson's test on D.C. machines is conducted at |
| A. | no-load |
| B. | part load |
| C. | full-load |
| D. | overload |
| Answer» C. full-load | |
| 108. |
During rheostat braking of D.C. series motors |
| A. | motor is run as a generator |
| B. | motor is reversed in direction |
| C. | motor is run at reduced speed |
| D. | all |
| Answer» A. motor is run as a generator | |
| 109. |
For which types of D.C. motor, dynamic braking is generally used ? |
| A. | Shunt motors |
| B. | Series motors |
| C. | Compound motors |
| D. | All of the above |
| Answer» D. All of the above | |
| 110. |
Which method of braking is generally used in elevators ? |
| A. | Plugging |
| B. | Regenerative braking |
| C. | Rheostatic braking |
| D. | None of the above |
| Answer» A. Plugging | |
| 111. |
In variable speed motor |
| A. | a stronger commutating field is needed at low speed than at high speed |
| B. | a weaker commutating field is needed at low speed than at high speed |
| C. | same commutating field is needed at low speed than at high speed |
| D. | none of the above is correct |
| Answer» B. a weaker commutating field is needed at low speed than at high speed | |
| 112. |
When the armature of a D.C. motor rotates, e.m.f. induced is |
| A. | self-induced e.m.f. |
| B. | mutually induced e.m.f. |
| C. | back e.m.f. |
| D. | none of the above |
| Answer» C. back e.m.f. | |
| 113. |
Where D.C. motor of H.P. 12 or more requires frequent starting, stopping,reversing and speed control |
| A. | drum type controller is used |
| B. | three point starter is used |
| C. | four point starter is used |
| D. | all above can be used |
| Answer» A. drum type controller is used | |
| 114. |
If a D.C. shunt motor is working at full load and if shunt field circuit suddenlyopens |
| A. | this will make armature to take heavy current, possibly burning it |
| B. | this will result in excessive speed, possibly destroying armature due toexcessive centrifugal stresses |
| C. | nothing will happen to motor |
| D. | motor will come to stop |
| Answer» A. this will make armature to take heavy current, possibly burning it | |
| 115. |
D.C. motor is to drive a load which has certain minimum value for most of thetime and some peak value for short duration. We will select the |
| A. | series motor |
| B. | shunt motor |
| C. | compound motor |
| D. | any of the above |
| Answer» A. series motor | |
| 116. |
D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this |
| A. | series motor |
| B. | shunt motor |
| C. | compound motor |
| D. | any of the above |
| Answer» C. compound motor | |
| 117. |
Which D.C. motor has got maximum self relieving property ? |
| A. | Series motor |
| B. | Shunt motor |
| C. | Cumulatively compounded motor |
| D. | Differentially compounded motor |
| Answer» A. Series motor | |
| 118. |
In the D.C. motor the iron losses occur in |
| A. | the field |
| B. | the armature |
| C. | the brushes |
| D. | the commutator |
| Answer» B. the armature | |
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