Synopsis of Electrical Engineering

Important Multiple Choice Questions On Electrical Machines 1. Supply to one terminal of delta-star three-phase core type transformer which is on no-load fails. Assuming magnetic circuit symmetry, voltages on the secondary side will be 230, 230,115 230,115, 115 345, 115, 115 345, 0, 345 2. A 220/440 V, 50Hz, 5kVA single phase transformer operates on 220V, 40 Hz supply with secondary winding. Then The eddy current loss and hysteresis loss of the transformer decrease The eddy current loss and hysteresis loss of the transformer increase The hysteresis loss of the transformer increases while eddy current loss remains the same The hysteresis loss remains the same whereas eddy current loss decreases 3. The voltage regulation of a large transformer is mainly influenced by No-load current and load power factor Winding resistances and load power factor Leakage fluxes and load power factor Winding resistances and core losses 4. If a sinus

Important Multiple Choice Questions On Power Systems 1. With 100 % inductive shunt compensation, the voltage profile is flat for 100% loading line 50% loading line Zero loading of line None of these 2. For a long uncompensated line the limit to the line loading is governed by Thermal limit Voltage drop Stability limit Corona loss 3. Series capacitive compensation in EHV transmission lines is used to Reduce the line loading Improve   the stability of the system Reduce the voltage profile Improves the protection of the line 4. The main consideration for higher and higher operating voltage of transmission is to Increase the efficiency of transmission Reduce power losses Increase power transmission capability Both (A) and (B) above 5. The inertia constant H of a machine of 200MVA is 2 p.u. its value corresponding to 400MVA will be 4 2 1 0.5 6. A 500MVA, 11kV synchronous generator has 0.2 p.u. synchronous re

Important multiple choice questions on power system 1.        A line trap in carrier current relaying tuned to carrier frequency presents A)      High impedance to carrier frequency but low impedance to power frequency B)       Low impedance to both carrier and power frequency C)       High impedance to both carrier and power frequencies D)      Low impedance to carrier frequency and high impedance to power frequency 2.        The use of fast acting relays and circuit breakers for clearing a sudden short circuit on a transmission link between generator and the receiving end bus improves the transient stability of the machine because A)      Short circuit current becomes zero B)       Post-fault transfer impedance attains a value higher than that during the fault C)       Ordinate of the post-fault power-angle characteristic is higher than that of during fault characteristic D)      Voltage behind the transient reactance increases to a higher value 3.        A

Important Multiple Choice Questions on Electrical Machines 1.        Transformer excited from a sinusoidal voltage source will draw a no-load current which A)      Is sinusoidal and of the same frequency as the voltage source B)       Comprises the fundamental frequency (same as that of the voltage source) and the peaking third harmonic C)       Comprises the fundamental frequency and the depressing third harmonic D)      Is sinusoidal of frequency three times that of the voltage source 2.        A transformer on no-load is switched on to a source of voltage. It will draw a current which A)      The same as the steady-state magnetizing current B)       Several times the steady-state magnetizing current depending upon the initial state of the residual flux in the transformer core C)       Several times the steady-state magnetizing current depending upon the initial state of the residual flux in the transformer core D)      Twice the steady-state magnetizing curre

Important Multiple Choice Questions in Electrical Machines 1.        A single phase transformer when supplied from 220V, 50 Hz has eddy current loss of 50 W. If the transformer is connected to a voltage of 330V, 50 Hz, the eddy current loss will be A)      168.75 W B)       112.5 W C)       75 W D)      50 W 2.        A coil wound on magnetic core is excited from an AC voltage source. The source voltage and its frequency are both doubled. The eddy current loss in the core will become A)      Half B)       Remains same C)       Double D)      Four times 3.        Building steel core out of stampings reduces eddy current loss because it A)      Increases core resistivity B)       Increases the effective length of eddy currents paths thereby increasing effective resistance to the flow of eddy currents C)       Increases core permeability D)      Reduces the effective length of eddy current path, thereby reducing effective resistance to the flow of eddy cu