# A synchronous motor is essentially a motor with

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A synchronous motor is essentially a motor with

(a) Constant speed (b) Leading power factor (c) Unity power factor (d) Lagging power factor

## Related questions

The maximum possible power of a 3-phase synchronous motor with synchronous reactance 0.8 p.u. connected to a bus-bar of 1.0 p.u. and excitation adjusted to 1.2 p.u. is (A) 0.5 p.u. (B) 0.96 p.u. (C) 1.5 p.u. (D) 1.8 p.u.

A cylindrical rotor synchronous motor is switched on to the supply with its field windings shorted on themselves, the motor will .  A) Not start B) Start but will not run at synchronous speed C) Start as an induction motor and then run as a synchronous motor D) Start and run as a synchronous motor

The effect of increasing load on a synchronous motor running with normal excitation is (A) Increase both its Ia and power factor. (B) Decrease Ia, but increase power factor. (C) Increase Ia, but decrease power factor (D) Decrease both Ia and power factor.

When running under no-load condition and with over excitation, armature current Ia drawn by a synchronous motor

In a synchronous motor which losses varies with load?

Tachometer works essentially as a generator with output voltage proportional to magnitude of the : - a) Angular Velocity of the shaft b) Torque of the shaft c) Temperature of the shaft d) Back Lash of the shaft

A synchronous motor operates at 0.8 pf lagging. If the field current of the motor is continuously increased  1. The power factor decreases upto a certain value of field current and thereafter it increases.  2. The armature current increases upto a certain value of field current and thereafter it decreases.  3. The power factor increases upto a certain value ... field current and thereafter it, increases.  From these, the correct answer is (a) 1, 2 (b) 3, 4 (c) 1, 3 (d) 2, 4

A synchronous motor at no load condition is known as synchronous condenser and improves the (a) stability (b) efficiency (c) power factor (d) frequency of the integrated system

The maximum torque that a synchronous motor can deliver is proportional to (1) 1/V2 (2) 1/V (3) V (4) V2

When a synchronous motor is started, the field winding is initially :  a)excited by a d.c. sources b) short circuited c) open circuited d) none of these

A synchronous motor is delivering 80% of its rated output and is operating at UPF. If its excitation is increased, then  (1) the output delivered gets increased (2) its pf becomes lagging (3) the output delivered gets decreased (4) its pf becomes leading

If a four pole synchronous generator driven at 1500 rpm feeds a 6-pole induction motor, which is loaded to run at a slip of 5%, then speed of the motor will be   (a) 1000 rpm (b) 950 rpm (c) 1500 rpm (d) 1450 rpm

In a synchronous motor, damper winding is provided to   (a) stabilize rotor motion (b) suppress rotor oscillations (c) develop necessary starting torque (d) (b) and (c) both

A 3~phase synchronous motor, connected to infinite bus, is operating at no load at normal excitation. The field excitation of the motor is first decreased to zero and then increased in the reverse direction. The armature current of the synchronous motor will:  (1) Remain constant. (2) First decrease and then increase, (3) Increases continuously (4) First increase and then decreased

What type of excitation is given to the rotor winding of a synchronous motor?  (A) DC supply at 100 -250 V (B) AC supply at 400 V (C) Revolving field (D) Induction from stator currents

A controller essentially is a/an   (a) Amplifier (b) Sensor (c) Comparator (d) Clipper

Load cell essentially is a   (a) Thermistor (b) Strain gauge (c) Photo-voltaic cell (d) None of these

In synchronous motor, does the winding losses vary with load?

A synchronous machine with large SCR has (1) Poor voltage regulation (2) Poor stability (3) Low short circuit current (4) More synchronizing power

The synchronous motor can be used as a capacitor • By increasing excitation • By decreasing excitation • By increasing speed • By decreasing speed

A 12 -pole, 440 V, 50 Hz, 3 -phase synchronous motor takes a line current of 100 A at 0.8 pf leading. Neglecting losses, the torque developed will be

The speed of a synchronous motor depends upon  (1) supply voltage (2) supply frequency (3) number of poles (4) both supply frequency and number of poles

Variation in dc excitation of a synchronous motor causes variation in   (a) Speed of motor (b) Power factor (c) Armature current (d) Both armature current and power factor

In a 3-phase synchronous motor;  (A) the speed of the stator MMF is always more than that of the rotor MMF (B) the speed of the stator MMF is always less than that of the rotor MMF (C) the speed of the stator MMF is synchronous speed while that of the rotor MMF is zero (D) the rotor and the stator MMF are stationary with respect to each other

Maximum power developed in a synchronous motor occurs at a coupling angle of:  (A) 120° (B) 60° (C) 90° (D) 0°

The synchronous speed of an 8 pole induction motor supplied power from a 50 Hz source will be ?

A load cell essentially represents a . (A) Thermocouple (B) Thermistor (C) Photo -conductive device (D) Strain gauge

Synchronous motor is found more economical when the load is above (1) 2 kW (2) 20 kW (3) 50 kW (4) 100 kW

When excitation of synchronous motor is increased upto normal excitation from under excitation, armature current   (a) increases (b) decreases (c) remains constant (d) None of the above

What is back EMF of synchronous motor?

A dc shunt motor runs at 500 r.p.m at 220 V. A resistance of 4.5 Ω is added in series with the armature for speed control. The armature resistance is 0.5 ohms. The current to stall the motor will be (1) 44 A (2) 50 A (3) 44.4 A (4) 60 A

A salient pole synchronous motor is running at no load. Its field current is switched off, the motor will (a) come to stop. (b) continue to run at synch. speed. (c) continue to run at a speed slightly less than synch. speed. (d) continue to run at a speed slightly more than the synch. speed.

In a synchronous motor, if β is impedance angle and δ is torque angle, then the maximum developed mechanical power is obtained when (a) δ = 180 – 2β (b) δ = 2β (c) δ = 180 – β (d) δ = β

A three phase, salient pole synchronous motor is connected to an infinite bus. It is operated at no load a normal excitation. The field excitation of the motor is first reduced to zero and then increased in reverse direction gradually. Then the armature current.  (A) Increases continuously (B) First increases and then decreases steeply (C) First decreases and then increases steeply (D) Remains constant

A three-phase synchronous motor connected to ac mains is running at full load and unity power factor. lf its shaft load is reduced by half and field current is held constant then its new power factor will be

The maximum power in a synchronous motor (for a given excitation) is produced when the power angle is equal to: (A) 0° (B) 45° (C) 60° (D) 90°

A controller, essentially, is a ?

The advantage of synchronous motor over slip -ring induction motor are that it's (A) Power factor can be vaned (B) Speed can easily varied (C) Speed is independent of supply frequency (D) Rotor has two slip rings

An ideal synchronous motor has no starting torque because the  (a) Rotor is made up of salient poles. (b) Relative velocity between the stator and rotor mmfs is zero. (c) Relative velocity between stator and rotor mmfs is not zero. (d) Rotor winding is highly inductive.

A 3-phase induction motor under locked rotor condition and with stator supply, induces (A) small voltage at slip frequency (B) large voltage at rotor frequency (C) zero voltage at zero frequency (D) large voltage at slip frequency