EM-III BITS
1. In a 3-phase synchronous motor (comment on the position of field mmf,air gap flux & armature mmf)
b. The armature mmf leads the air-gap flux and air-gap flux leads the field mmf
2. An Ideal synchronous motor has no starting torque because ? [01D02]
c. relative velocity between the stator and the rotor mmfs is zero
3. In a synchronous motor [01M01]
b. the rotor mmf and stator mmf are stationary with respect to each other
4. In a 3-phase synchronous motor the magnitude of field flux [01M02]
a. remains constant at all loads
5. The armature current of a synchronous motor on no load [01M03]
d. Leads the applied voltage by 900
6. In construction, synchronous motor is similar to an [01S01]
d. Alternator
7. Number of slip rings in a 3.phase synchronous motor ? [01S02]
c. 2
8. In synchronous motors,at what speeds the stator field and rotor field rotates ?
a. same speed
9. A 3-phase synchronous motor needs dc supply for excitation [01S04]
c. continuously
10. Which type of motors are the doubly excited magnetic systems ? [01S05]
a. synchronous motors
11. A cylindrical rotor synchronous motor is switched on to the supply with its field windings shorted on themselves it will [02D01]
a. not start
12. The rotor of a synchronous motor can only run at synchronous speed of the stator magnetic field due to ?[02D02]
d. Interlocking action between stator and rotor fields
13. 3-phase synchronous motors need what type of supply?[02M01]
d. 3-phase ac supply as well as d.c supply
14. A synchronous motor is operating with normal excitation with the increase in load the armature current drawn from the supply mains increases due to ?[02M02]
c. Increase in resultant voltage across the armature
16. Rotor winding of a synchronous motor is excited by [02S01]
a. dc supply at 100-250V
17. The relative speed between the magnetic fields of stator and rotor under steady state operation is zero for [02S02]
d. synchronous machine
18. A synchronous motor operating with normal excitation adjusts to increased load due to increase in [02S03]
a. armature current
19. In a synchronous motor, under operating conditions, the angle between induced voltage and supply voltage will be [02S04]
c. between 900 and 1800
20. The magnitude of emf induced the armature of a synchronous motor (Eb) depends upon [02S05]
a. rotor excitation
21. In a synchronous motor electro-magnetic power varies [03D01]
a. directly as applied voltage
22. synchronous power equation of a synchronous motor. is known as ?[03D02]
b. Phase displacement angle
23. Synchronizing power of a synchronous motor varies [03G03]
c. inversely as the synchronous reactance
24. A 3-phase ,400V,50Hz synchronous motor is operation normally. If the load on the motor is doubled keep the excitation constant,the new load angle will become nearly
b. double
26. Torque angle δ is defined as the space angle between ?[03S01]
c. stator field axis and rotor field axis
27. In a synchronous motor torque or load angle δ _ _ _ _ _ _ with increase in load
c. Increases
28. The value of load angle for a synchronous motor is minimum when the motor is operating on?
a. No load
29. The value of load angle for a synchronous motor depends mainly upon its
b. Load
30. The mechanical displacement of the rotor field axis with respect to stator field axis in a synchronous motor running on full load is of the order of [03S05]
b. 50
31. A synchronous motor, connected to an infinite bus, is working at a leading power factor. Its excitation voltage `Ef' and terminal voltage `Vt' are related as under [04D01]
c. Ef > Vt and Ef leadsVt
32. A synchronous motor operating at rated voltage draws 1.0 p.u current at 1.0 power factor. The machine parameters are synchronous reactance 1.0 pu.armature resistance negligible.Apart from supplying this rated power, if the motor has to supply an additional reactive power of 0.8 pu,then the field current has to be increased by [04D02]
b. 46 %
33. A synchronous motor can operate over a wide range of power factors, i.e from lagging to leading power factor this is achieved by [04M01]
a. changing the field excitation
34. A sychronous motor fed from an infinite bus is at half-full load. If an increase in the field current a reduction in the armature current, then the motor [04M02]
d. absorbing reactive power from the bus at lagging p.f
36. Maximum power in cylindrical and salient-pole machines obtained respectively at load angles of
c. 900,<900
37. In synchronous motor minimum armature current corresponds to ?[04S02]
d. Unity power factor
38. The motor with highest efficiency ?[04S03]
c. Synchronous motor
39. A synchronous motor will deliver maximum power when [04S04]
a. load angle is equal to input power angle
40. A 3-phase synchronous motor will operate on lagging power factor till [04S05]
b. E0 <V sinθ
43. The disadvantage of synchronous condenser when compared to static capacitors is [05M01]
d. fall out of synchronism & cost is higher than static capacitors
44. The voltage at the end of a transmission line can be controlled by installing a _ _ _ _ _ _ at the end of the transmission line [05M02]
a. synchronous condenser
45. A rise of voltage at the motor terminals tends to cause the motor to operate a. under excited and draw lagging current
46. By varying the load on the motor, the paths of the phasor and phasor I follow a circle. The locus is known as [05S01]
a. excitation circle
47. In V- curves the armature current is minimum, the power factor is unity and the corresponding field current is known as [05S04]
d. Normal field current (or) excitation
48. At no load synchronous motor draws small current from the supply mains to meet [05S05]
b. Internal losses
49. A salient pole synchronous motor continues rotating even if its excitation current is reduced to zero. This is due to? [06D01]
d. magnetization of rotor salient poles by stator magnetic field.
50. A 3-phase synchronous motor connected to an infinite bus-bar, with constant excitation is driving a certain load and operating at leading power factor. If the shaft load is reduced. [06D02]
b. the load angle will decrease
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