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Recent questions and answers in Synchronous machine

1 answer 28 views

The number of electrical degrees ‘passed through’ in one revolution of a 6-pole synchronous alternator is: A) 360 degree B) 720 degree C) 1080 degree D) 2160 degree

answered Jun 17, 2018 in Synchronous machine
0 answers 40 views

The ratio of air-gap line voltage from open-circuit characteristic and armature current from short-circuit characteristic for a particular value of the field current in a synchronous generator is (A) synchronous reactance (B) synchronous impedance (C) unsaturated synchronous reactance (D) unsaturated synchronous impedance 

asked Jun 4, 2018 in Synchronous machine
0 answers 42 views

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

asked Jun 4, 2018 in Synchronous machine
0 answers 29 views

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

asked Jun 4, 2018 in Synchronous machine
0 answers 19 views

Two 3-phase synchronous generators with reactance 60% and 40% feed a fault current of 1200 A up to short-circuit fault point. The short-circuit current is (A) 1200 A (B) 2400 A (C) 4000 A (D) 5000 A 

asked Jun 4, 2018 in Synchronous machine
0 answers 20 views

The active power of a synchronous generator can be varied mainly by (a) changing field excitation (b) changing of prime mover speed (c) both (a) and (b) (d) none of the above

asked May 25, 2018 in Synchronous machine
0 answers 16 views

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. 

asked May 25, 2018 in Synchronous machine
0 answers 26 views

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. 

asked May 25, 2018 in Synchronous machine
0 answers 12 views

Armature reaction mmf and leakage reactance of a synchronous machine are determined by (a) open circuit test and short circuit test (b) open circuit test and zero power factor test (c) zero power factor test only (d) short circuit test only  

asked May 25, 2018 in Synchronous machine
0 answers 16 views

A synchronous motor works as synchronous condenser when it operates (a) under excited with leading power factor (b) normal excited with unity power factor (c) over excited with leading power factor (d) over excited with lagging power factor 

asked May 25, 2018 in Synchronous machine
0 answers 14 views

Use of double line to transmit power is helpful in (a) increasing power capability (b) increasing stability (c) both (a) and (b) (d) decreasing power capability 

asked May 25, 2018 in Synchronous machine
0 answers 35 views

A suspension insulator string has three units with ground capacitance of 0.2 C and self capacitance of C. Its string efficiency is (a) 75% (b) 78% (c) 80% (d) 85%

asked May 25, 2018 in Synchronous machine
0 answers 9 views

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  

asked May 25, 2018 in Synchronous machine
1 answer 46 views

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

answered May 20, 2018 in Synchronous machine
1 answer 24 views

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

answered May 20, 2018 in Synchronous machine
1 answer 14 views

A stand alone engine driven synchronous generator is feeding a partly inductive load. A capacitor is now connected across the load to completely nullify the inductive current. For this operating condition.  (A) the field current and fuel input have to be reduced (B) the field current and fuel input have to be increased (C) the field current has to be increased and fuel input left unaltered (D) the field current has to be reduced and fuel input left unaltered

answered May 17, 2018 in Synchronous machine
1 answer 26 views

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

answered May 17, 2018 in Synchronous machine
1 answer 16 views

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.

answered May 17, 2018 in Synchronous machine
1 answer 18 views

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

answered May 17, 2018 in Synchronous machine
1 answer 17 views

A 100 kVA, 415 V(line), star-connected synchronous machine generates rated open circuit voltage of 415 V at a field current of 15 A. The short circuit armature current at a field current of 10 A is equal to the rated armature current. The per unit saturated synchronous reactance is  (A) 1.731 (B) 1.5 (C) 0.666 (D) 0.577

answered May 17, 2018 in Synchronous machine
1 answer 15 views

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

answered May 17, 2018 in Synchronous machine
1 answer 11 views

The angle δ in the swing equation of a synchronous generator is the  (A) angle between stator voltage and current (B) angular displacement of the rotor with respect to the stator (C) angular displacement of the stator mmf with respect to a synchronously rotating axis. (D) angular displacement of an axis fixed to the rotor with respect to a synchronously rotating axis

answered May 17, 2018 in Synchronous machine
1 answer 30 views

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

answered May 17, 2018 in Synchronous machine
1 answer 115 views

A 500 MVA, 11 KV synchronous generator has 0.2 p.u. synchronous reactance. The p.u. synchronous reactance on the base values of 100 MVA and 22 KV is  A) 0.16 B) 0.01 C) 4.0 D) 0.25

answered May 17, 2018 in Synchronous machine
1 answer 6 views

During hunting of synchronous motor  A) Negative phase sequence currents are generated B) Harmonics are developed in the armature current C) Damper bars develop torque D) Field excitation increases 

answered May 17, 2018 in Synchronous machine
1 answer 27 views

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

answered Mar 20, 2018 in Synchronous machine
1 answer 19 views

When the stator windings are connected in such a fashion that the number of poles are made half, the speed of the rotor of a synchronous motor?

answered Mar 20, 2018 in Synchronous machine
1 answer 28 views

The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as?

answered Mar 20, 2018 in Synchronous machine
0 answers 37 views

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?

asked Mar 20, 2018 in Synchronous machine
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