GATE EE
Electrical Machines
Synchronous Machines
Previous Years Questions

## Marks 1

A star-connected 3-phase, 400 V, 50 kVA, 50 Hz synchronous motor has a synchronous reactance of 1 ohm per phase with negligible armature resistance. T...
In a salient pole synchronous motor, the developed reluctance torque attains the maximum value when the load angle in electrical degrees is
If a synchronous motor is running at a leading power factor, its excitation induced voltage (Er) is
A three-phase, 50Hz, star-connected cylindrical-rotor synchronous machine is running as a motor. The machine is operated from a 6.6 kV grid and draws ...
In a synchronous machine, hunting is predominantly damped by
A star connected 400 V, 50 Hz, 4 pole synchronous machine gave the following open circuit and short circuit test results: Open circuit test: VOC = 40...
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 ...
Distributed winding and short chording employed in AC machines will result in
In a stepper motor, the detent torque means
A three phase synchronous motor connected to ac mains is running at full load and unity power factor. If its shaft load is reduced by half, with field...
A synchronous generator is feeding a zero power factor (lagging) load at rated current the armature reaction is
In relation to the synchronous machines, which one of the following statements is false?
For a given stepper motor, the following torque has the highest numerical value.
The following motor definitely has a permanent magnet rotor
Curves X and Y in Figure denote open circuit and full-load zero power factor (zpf) characteristics of asynchronous generator. Q is a point on the zpf ...
A stand-alone engine driven Synchronous generator is feeding a partly inductive load. A capacitor is now connected across the load to completely nulli...
It is desirable to eliminate 5th harmonic voltage from the phase voltage of an alternator. The coils should be short-pitched by an electrical angle of...
Figure shows the magnetization curves of an alternator at rated armature current, unity power factor and also at no load. The magnetization curve for ...
Xd, Xd' and Xd" are steady stated-axis synchronous reactance, transient d-axis reactance and sub-transient d-axis reactance of a synchronous machine r...
The phase sequence of a three-phase alternator will reverse if
Higher synchronous reactance is preferred in the present day alternators, because one can have
A synchronous generator connected to an infinite bus is overexcited. Considering only the reactive power, from the point of view of the system, the ma...
During hunting of synchronous motor
In Figure. The characteristic that corresponds to the variation of synchronous reactance of synchronous motor with field current is ...
A synchronous motor on load draws a current at a leading power factor angle $$\phi$$. If the internal power factor angle – which is the phase angle be...
The torque angle of a synchronous machine operating from a constant voltage bus, is usually defined as the space angle between
The developed electromagnetic force and or torque in electro $$-mechanical energy conversion systems act in a direction that tends ## Marks 2 A$$3$$-phase,$$2$$-pole,$$50Hz,$$synchronous generator has a rating of$$250MVA,0.8pf$$lagging. The kinetic energy of the mac... Two generating units rated$$300MW$$and$$400MW$$have governor speed regulation of$$6\% $$and$$4\% $$respectively from no load to full... A$$25kVA,400V,\Delta $$- connected,$$3$$-phase, cylindrical rotor synchronous generator requires a field current of$$5A$$... Two parallel connected, three-phase,$$50Hz,11kV,$$star-connected synchronous machines$$A$$and$$B,$$are operating as synchronous condensers.... A three-phase,$$50Hz$$salient-pole synchronous motor has a per-phase direct-axis reactance$$\left( {{X_d}} \right)$$of$$0.8pu$$and a p... A three-phase,$$11kV,50Hz,2$$pole, star connected, cylindrical rotor synchronous motor is connected to an$$11kV,50$$... A non-salient pole synchronous generator having synchronous reactance of$$0.8pu$$is supplying$$1pu$$power to a unity power factor load a... There are two generators in a power system. No-load frequencies of the generators are$$51.5Hz$$and$$51Hz,$$respectively, and both are ha... A$$20$$-pole alternator is having$$180$$identical stator slots with$$6$$conductors in each slot. All the coils of a phase are in series. If the c... A synchronous generator is connected to an infinite bus with excitation voltage$${E_f} = 1.3\,pu.$$The generator has a synchronous reactance of$$1....
A three phase synchronous generator is to be connected to the infinite bus. The lamps are connected as shown in the figure for the synchronization. Th...
The direct axis and quadrature axis reactances of a salient pole alternator are $$1.2$$ $$p.u$$ and $$1.0$$ $$p.u$$ respectively. The armature resista...
A $$50$$ $$Hz$$ synchronous generator is initially connected to a long lossless transmission line which is open circuited at the receiving end. With t...
A separately excited $$dc$$ machine is coupled to a $$50Hz,$$ three-phase, 4-pole induction machine as shown in the figure. The dc machine is energize...
A field excitation of $$20A$$ in a certain alternator results in a armature current of $$400$$ $$A$$ in short circuit and a terminal voltage of $$2000... A synchronous motor is connected to an infinite bus at$$1.0p.u$$voltage and draws$$0.6pu$$at unity power factor. Its synchronous reacta... A synchronous motor is connected to an infinite bus at$$1.0p.u$$voltage and draws$$0.6pu$$at unity power factor. Its synchronous reactance ... A$$100kVA$$,$$415V,$$star connected synchronous machine generates rated open circuit voltage$$415V$$at a field current of$$15A.$$The shor... A$$3$$phase,$$3$$stack, variable reluctance stepper motor has$$20$$poles on each rotor and stator stack. The step angle of this stepper motor is... A$$3$$-phase$$4000V,5kW,$$star connected synchronous motor having an internal reactance of$$10ohms$$is operating at$$50\% $$... A$$4$$pole,$$50Hz,$$synchronous generator has$$48$$slots in which a double layer winding is house. Each coil has$$10$$turns and is short... A$$4$$pole,$$50Hz,$$synchronous generator has$$48$$slots in which a double layer winding is house. Each coil has$$10$$turns and is short... A$$1000kVA,6.6kV,3$$-phase star connected cylindrical pole synchronous generator has a synchronous reactance of$$20\Omega .$$Ne... A$$1000kVA,6.6kV,3$$-phase star connected cylindrical pole synchronous generator has a synchronous reactance of$$20\Omega .$$Ne... The synchronous speed for the seventh space harmonic$$mmf$$wave of a$$3$$-phase,$$8$$pole,$$50Hz$$induction machine is Two$$3$$-phase,$$Y$$-connected alternators are to be paralleled to a set of common bus bars. The armature has a per phase synchronous reactance of ... A$$400V,50kVA,0.8pf$$leading delta connected,$$50Hz$$synchronous machine has a synchronous reactance of$$2ohm$... For a $$1.8$$ degree, $$2$$-phase bipolar stepper motor, the stepping rate is $$100$$ steps/second. The rotational speed of the motor in $$rpm$$ is A $$500$$ $$MW$$ $$3$$-phase $$Y$$-connected synchronous generator has a rated voltage of $$21.5kV$$ at $$0.85$$ $$pf.$$ The line current when operati... A hydraulic turbine having rated speed of $$250$$ $$rpm$$ is connected to a synchronous generator. In order to produce power at $$50$$ $$Hz,$$ the num... A $$4$$-pole, $$3$$-phase, double layer winding is housed in a $$36$$-slot stator for an $$ac$$ machine with $$60$$ degree phase spread. Coil span is ... The flux per pole in a synchronous motor with the field circuit ON and the stator disconnected from the supply is found to be $$25$$ $$mWb.$$ When the... A star-connected 440 V, 50 Hz alternators has per phase synchronous reactance of 10 Ω. It supplies a balanced capacitive load current of 20 A, as show... A single-phase, 2000 V alternator has armature resistance and reactance of 0.8 ohms and 4.94 ohms respectively. The voltage regulation of the alternat... A three phase alternator is wound with a 60 degree phase-spread armature windings and develops 300 kVA. If the armature is reconnected utilizing all t... The armature of a single phase alternator is completely wound with T single turn coils distributed uniformly. The induced voltage in each turn is 2 Vo... A single-phase alternator has a synchronous reactance of $$2$$ $$ohms$$ and negligible resistance. If it supplies $$10$$ $$A$$ to a purely capacitive ... A three phase alternator has negligible stator resistance. A short circuit test is conducted on this alternator. At a particular speed a field current... Two $$550$$ $$kVA$$ alternators operate in parallel to supply the following loads $$(i)$$ $$250$$ $$kW$$ at $$0.95$$ power factor lag $$(ii)$$ $$100... A synchronous motor operates at$$0.8p.f.$$lagging. If the field current of the motor is continuously increased$$(1)$$the power factor decrea... ## Marks 5 A$$415V,2$$pole,$$3$$phase,$$50Hz,$$star connected, non-salient pole synchronous motor has synchronous reactance of$$2\,\Omega$...
A $$50$$ $$kW$$ synchronous motor is tested by driving it by another motor. When the excitation is not switched on, the driving motor takes $$800$$ $$... Two identical synchronous generators, each of$$100MVA,$$are working in parallel supplying$$100MVA$$at$$0.8$$lagging$$p.f.$$at rated ... A$$2300V,3$$-phase synchronous motor driving a pump is provided with a line ammeter and a field rheostat. When the rheostat is adjusted suc... A$$5MVA$$,$$11kV$$,$$3$$-phase star connected alternator is synchronized to the bus bars and is operating with an induced$$EMF$$of$$125\% $$of ... The per unit voltage of two synchronous machines connected through a lossless line are$$0.95\,\,\angle \,{10^0}\,\,$$and$$1.0\,\,\angle \,{0^0}\,\,...
The distribution factor for a $$36$$ slot stator with three-phase, $$8$$-pole winding, having $${120^ \circ }$$ phase Spread, is _________
Figure depicts the load characteristics of an constant speed. Match the following sets of operating conditions with the given characteristics. Disrega...
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