Objective Questions on Alternator for Electrician Trade
| Sr. No. | Questions with options |
| 1 | Which rule is used to find the direction of induced emf in an alternator?
(a) Cork screw rule (b) Right hand palm rule (c) Fleming’s left hand rule (d) Fleming’s right hand rule Ans – (d) |
| 2 | How alternators are rated?
(a) KVA (b) KW (c) MW (d) KV Ans- (a) |
| 3 | What is the supply frequency of an alternator having 6 poles runs at 1000 rpm?
(a) 25 Hz (b) 40 Hz (c) 50 Hz (d) 60 Hz Ans-(c) |
| 4 | Calculate the speed of an alternator having 2 poles at a frequency of 50 Hz?
(a) 1500 rpm (b) 2500 rpm (c) 2000 rpm (d) 6000 rpm Ans –(c) |
| 5 | What condition the lamps become dark in dark lamp method of parallel operation of two alternators?
(a) Terminal voltages are equal (b) Voltage and frequency are equal (c) Voltage and power rating are equal (d) Frequency are same in both alternator Ans –(b) |
| 6 | How to compensate de-magnetizing effect due to armature reaction in an alternator?
(a) Reducing the speed of alternator (b) Reducing field excitation current (c) Increasing field excitation current (d) Increasing the speed of alternator Ans –(c) |
| 7 | What is the use of synchroscope?
(a) Adjust the output voltage (b) Adjust the phase sequence (c) Adjust the supply frequency (d) Indicate the correct instant for paralleling Ans –(d) |
| 8 | What is the name of the equipment that provides D.C to the rotor of alternator?
(a) Exciter (b) Inverter (c) Converter (d) Synchronizer Ans – (a) |
| 9 | What is the purpose of damper winding in alternator?
(a) Reduces the copper loss (b) Reduces windage losses (c) Reduces the hunting effect (d) Improves the voltage regulation Ans – (c) |
| 10 | Which condition is to be satisfied before parallel operation of alternators?
(a) Rating must be same (b) Phase sequence must be same (c) Rotor impedance must be same (d) Stator impedance must be same Ans – (b) |
| 11 | What is the speed of an alternator connected with a supply frequency of 50 Hz at rated voltage having 4 poles?
(a) 1000 rpm (b) 1500 rpm (c) 3000 rpm (d) 4500 rpm Ans – (b) |
| 12 | What condition the two lamps become bright and one lamp dark during paralleling of two alternators?
(a) Terminal voltages are equal (b) Voltages and frequencies are equal (c) Voltages and phase sequence are equal (d) Both the alternators receive same frequency Ans – (b) |
| 13 | What causes the terminal voltage of an alternator reduces, if the load increases?
(a) Field resistance (b) Armature reaction (c) Inductive reactance (d) Armature resistance Ans –(d) |
| 14 | What is the purpose of using damper winding in AC generator?
(a) Prevents heating (b) Reduces copper loss (c) Reduces windage loss (d) Prevent the hunting effect Ans – (d) |
| 15 | Calculate the speed in r.p.s of the 2 pole, 50 Hz alternator?
(a) 50 rps (b) 100 rps (c) 1500 rps (d) 3000 rps Ans-(a) |
| 16 | What is the advantage of using rotating field type alternator?
(a) Easy to locate the faults in the field (b) Easy to connect the load with alternator (c) Easy to dissipate the heat during running (d) Two slip rings only required irrespective of No. of phases Ans – (d) |
| 17 | What is the effect in increasing the field excitation current in alternator?
(a) Prevents demagnetizing (b) Over voltage protection (c) Dead short circuit protection (d) Alternator will be over loaded Ans – (a) |
| 18 | Calculate the pitch factor (KP) for a winding having 36 stator slots 4 pole with angle (alpha) is 30 degree in alternator?
(a) 0.942 (b) 0.965 (c) 0.978 (d) 0.985 Ans – (b) |
| 19 | What is the cause for hunting effect in alternators?
(a) Due to over load (b) Running without load (c) Running with fluctuation in load (d) Due to continuous fluctuation in load Ans –(d) |
| 20 | Calculate the voltage regulation in percentage if the load is removed from an alternator, the voltage rises from 480 V to 660 V?
(a) 0.272 (b) 0.325 (c) 0.375 (d) 0.385 Ans –(c) |
| Data Collected By – Rashmi | |
| Published On – 27th May 2022 | |
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