# Variation in dc excitation of a synchronous motor causes variation in

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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

## Related questions

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

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 DC Motor develops a torque of 150 N-m. A 10 percent reduction in the field flux causes a 50 percent increase in armature current. The new value of torque is: A) 102.5 N-m B) 202.5 N-m C) 172.5 N-m D) 232.5 N-m

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

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°

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

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.

In a variable speed induction motor derive V/f kept constant over a wide range of its frequency variation. The motor operates in the following mode : -  a) Constant power mode b) Constant torque mode c) Constant slip mode d) Variable power and variable torque mode

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

If we change the excitation of synchronous machine will it affect on motor speed?

what will happen when excitation of an unloaded salient pole synchronous motor suddenly gets disconnected?

A synchronous generator is feeding power to infinite bus bars at unity power factor. Its excitation is now increased. It will feed (a) The same power but at a leading power factor (b) The same power but at a lagging power factor (c) More power at unity power factor (d) Less power at unity power factor

In a synchronous generator if the excitation increased from a low value to normal value, with a fixed load  (A) The armature current increases and the power factor decreases  (B) The armature current decreases and the power factor also decreases  (C) The armature current decreases and the power factor increases but is lagging  (D) The armature current decreases and the power factor increases and is leading

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

In a 4-pole wave winding connected dc motor, the cross-magnetizing AT/pole for a brush shift of θ radians (A) Armature amp-conductors × (θ/360o) (B) Armature amp-turns × (θ/360o) (C) Armature amp-conductors × (1/4 - θ/360o) (D) Armature amp-conductors × (1/8 - θ/360o)

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

If the back emf of a dc motor is doubled and its speed is also doubled, the torque developed in the machine will  (1) get doubled (2) become 4 times (3) get halved (4) remain unaltered

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

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

What type of defect causes F -centers in a crystal ?  (a) Stoichiometric defect (b) Metal excess defect due to anion vacancies (c) Metal excess defect due to extra cations (d) Frenkel defect

An emf of 120 V causes a current of 3A to flow in a circuit how much energy is supplied by the source in 12 seconds. A. 4130 J B. 4310 J C. 4320 J D. None of these

Short circuit in a system causes which type of faults (1) Series (2) Shunt (3) Symmetrical (4) All of the above

If we change the excitation of synchronous machine will it affect on power factor?

A separately excited dc motor operating in first quadrant is fed from 3-phase semi -converter free -wheeling diode is open circuited, then the motor :  (A) can be operated in first quadrant (B) can be operated in first & second quadrants (C) can be operated in first & fourth quadrants (D) cannot be operated

In a DC motor, it is important to place the brushes along ______ A) Magnetic Neutral Axis B) Normal Geometric Axis C) Nominal Geometric Axis D) None of these

In a differentially compounded dc motor (A) the speed is constant as the torque increases (B) the speed falls non-linearly as the torque increases (C) the speed increases non-linearly as the torque increases (D) the flux increases as the load increases

A separately excited dc motor is required to be controlled, from a 3-phase supply, for its operation in the first quadrant only. The most preferred converter would be  (a) 3-phase fully controlled converter (b) 3-phase fully controlled converter with free wheel diode (c) 3-phase dual converter (d) 3-phase half wave converter

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

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 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

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

In a Synchronous motor, the magnitude of stator back e.m.f (Eb) depends on

A large dc motor is required to control the speed of the blower from a 3 -phase ac source. The suitable ac to dc converter is, 3 -phase (a) Fully controlled bridge converter (b) Fully controlled bridge converter with freewheeling diode (c) Half controlled bridge converter (d) Converter pair in sequence control

The method of speed control used for increasing the speed of a dc shunt motor above its rated speed is  1) armature resistance control 2) field control (3) armature voltage control (4) series parallel control

A 4 pole lap wound dc shunt motor rotates at the speed of 1500 rpm, having a flux of 0.4 mWb and total number of conductors 1000. The value of e.m.f. will be:  (A) 100 Volts (B) 0.1 Volts (C) 1 Volts (D) 10 Volts

If the load current and flux of a DC motor are held constant, and voltage applied across its armature is increased by 10%, its speed will:  (A) Decrease by 10%. (B) Remain unchanged. (C) Increase by 10%. (D) Increase by 20%.

What is the back EMF of a dc motor?