Synopsis of Electrical Engineering

Important Multiple Choice Questions on Electrical Machines 1.        Can a 50Hz transformer be used for a 25Hz if the input voltage is maintained constant at the rated value corresponding to 50Hz? a)       Yes. Since the voltage is constant, current levels will not change. b)       No. Flux will be doubled which will drive the core excessive saturation. c)        No. Owing to decreased reactance of transformer, input current will be doubled at load. d)       Yes. At constant voltage, insulation will not be overstressed. 2.        In a transformer, if the iron losses and copper losses are 40.5 kW and 50 kW respectively, then at what fraction of load will be the efficiency be maximum? a)       0.8 b)       0.57 c)        0.7 d)       0.9 3.        If the frequency of input voltage of the transformer is increased keeping the magnitude of voltage unchanged, then a)       Both the hysteresis and eddy current losses in the core will increase. b)       Hysteresis l

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.