Synopsis of Electrical Engineering

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

Important Multiple Choice Questions in Electrical Machines 1.        In a shaded pole induction motor, the rotor runs from the A)      Shaded portion to the unshaded portion of the pole while the flux in the former leads that of the latter B)       Shaded portion to the unshaded portion of the pole while the flux in the former lags that in the latter C)       Unshaded portion to the shaded portion while the flux in the former leads that it in the latter D)      Unshaded portion to the shaded portion  while the flux in the former lags that in the latter 2.        The torque of a reluctance motor can be effectively increased by A)      Increasing reluctance of the magnetic circuit along the direct axis B)       Decreasing the reluctance of the magnetic circuit along the quadrature axis C)       Increasing the ratio of the quadrature axis reluctance to direct axis reluctance D)      Decreasing the ratio of quadrature axis reluctance to direct axis reluctance 3.