# A pair of synchronous machines on the same shaft may be used to generate power at 60 Hz from given

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A pair of synchronous machines on the same shaft may be used to generate power at 60 Hz from given source of power at 50 Hz. Using minimum number of poles for both the machines, the synchronous speed will be (a) 500 r.p.m. (b) 600 r.p.m. (c) 1000 r.p.m. (d) 1200 r.p.m.

## Related questions

In relation to the synchronous machines, which on of the following statements is false ?  (A) In salient pole machines, the direct-axis synchronous reactance is greater than the quadrature-axis synchronous reactance. (B) The damper bars help the synchronous motor self start. (C) Short circuit ratio is the ratio of ... rated armature current. (D) The V-cure of a synchronous motor represents the variation in the armature current with field excitation, at a given output power.

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

When two synchronous machines are connected in parallel the synchronizing power tends to (A) accelerate the faster machine (B) retard the faster machine (C) retards the slower machine (D) pull the faster machine out of step

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If transformer frequency is changed from 60 Hz, to 60 Hz the ratio of eddy current loss 60 Hz to 50 Hz, at constant voltage will be?

An 8 pole wound rotor induction motor operating on 60 Hz supply is driven at 1800 r.p.m. by a prime mover in the opposite direction of revolving magnetic field. The frequency of the rotor current is (a) 30 Hz (b) 60 Hz (c) 120 Hz (d) 180 Hz

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The primary winding of a 220/6 V, 50 Hz transformer is energised from 110 V, 60 Hz supply. The secondary output voltage will be (A) 3.6 V. (B) 2.5 V. (C) 3.0 V. (D) 6.0 V.

The primary winding of a 220/6 V, 50 Hz transformer is energised from 110 V, 60 Hz supply. The secondary output voltage will be; (A) 3.6 (B) 2.5 V (C) 3.0 V (D) 6.0 V

A synchronous generator is feeding a zero power factor (lagging) load at rated current. The armature reaction is  (A) magnetizing (B) demagnetizing (C) cross-magnetizing (D) ineffective

A 100 MVA, 11 KV, 3-phase, 50 Hz, 8—pole synchronous generator has an inertia constant H equal to 4 seconds. The stored energy in the rotor of the generator at synchronous speed will be  A) 100 MJ B) 400 MJ C) 800 MJ D) 12.5 MJ

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

If the field of synchronous motor is under excited, power factor will be?

The corona loss in a 50 Hz system is 0.25 kW/ph/km. At a frequency of 60 Hz, the corona loss would be   (a) 0.30 kW/ph/km (b) 0.36 kW/ph/km (c) 028 kW/ph/km (d) 0.21 kW/ph/km

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

A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because?

The synchronous motor which works on leading power factor and does not drive any mechanical load is called?

How can a magnetic field be used to generate an electric current?

A three phase transformer can be used in emergency at reduced rating of 58% to deliver three phase power when it is connected (a) in star-delta (b) delta-star (c) star-star (d) delta-delta

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 single phase transformer rated at 3000 kVA, 69 kV 4.16 kV, 60 Hz has a total internal impedance Zp of 127 ohm, referred to the primary side. Calculate the primary current if the secondary is accidentally short circuited.  (A) 43.5 A (B) 543 A (C) 9006 A (D) 721 A

In a half-wave rectifier, if an a.c supply is 60 Hz. Then what is the a.c ripple at output? (A) 30 Hz (B) 60 Hz (C) 20 Hz (D) 15 Hz

What is the slip (as a percentage) when a 6 pole single phase induction motor operating on 220 V and 60 Hz is rotating at speed of 1140 rpm? A) 60% B) 5% C) 10% D) None of these

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A 500 MW, 3-phase, Y-connected synchronous generator has a rated voltage of 21.5 kV at 0.85 p.f. The line current when operating at full load rated conditions will be  (A) 13.43 kA (B) 15.79 kA (C) 23.25 kA (D) 27.36 kA

For a fault at the terminals of a synchronous generator, the fault current is maximum for a  A) 3-phase fault B) 3-phase to ground fault C) Line to ground fault D) Line to line fault

The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as?

A coil having 90 turns is connected to a 120 V, 60 Hz source. If the effective value of the magnetizing current is 4 A. Calculate the inductance of the coil.  (A) 79.6 mH (B) 121.2 mH (C) 32.2 mH (D) 83.16 mH

The power factor of a synchronous machine is controlled by (A) connected load (B) generated voltage (C) field current (D) load angle

A series RLC circuit resonate at 200 Hz. If the capacitance is increased to four times, the circuit will be in resonance at   (a) 100 Hz (b) 200 Hz (c) 400 Hz (d) 800 Hz

The damping winding in synchronous motor is generally used to?

A 60 Hz, 2 pole alternator should run at • a. 3000 r.p.m. c. 1500 r.p.m. • b. 3600 r.p.m. d. 1800 r.p.m.

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.

A 3 Phase, 60 Hz generator connected in Y connection, generates a line to line voltage of 23900 V. Calculate the peak line voltage.  (A) 13800 V (B) 33800 V (C) 42300 V (D) 23900 V

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

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

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

The back emf of synchronous motor depends on?

Hunting in synchronous motor cannot be due to?