(41) If the iron core of a transformer is replaced by an air core, then the hysteresis losses in the transformer will
(a) Increase
(b) Decrease
(c) Remain constant
(d) Becomes zero
(42) The flux created by the current flowing through the primary winding induces emf in
(a) Primary winding only
(b) Secondary winding only
(c) Transformer core only
(d) Both primary and secondary windings.
(43) The iron core in a transformer provides a ________ path to the main flux.
(a) low reluctance
(b) low resistance
(c) high reluctance
(d) high conductivity
(44) The joints in the transformer core laminations are staggered so as to
(a) avoid undue humming noise
(b) avoid continuous gap causing increase in magnetizing current
(c) increase the mechanical strength of the assembled core
(d) All of the above
(45) For CRGOS mitred overlap is preferred for the core-yoke joints as it
(a) improves the mechanical strength
(b) reduces magnetostriction
(c) reduces the magnetizing current and also the core losses
(d) makes better use of core space
(46) Tappings of a transformer are provided
(a) at the phase end of LV side
(b) at the phase end of HV side
(c) at the neutral end of HV side
(d) at the middle of HV side
(47) In operating a 400 Hz transformer at 50 Hz
(a) only voltage is reduced in the same proportion as the frequency
(b) only kVA rating is reduced in the same proportion as the frequency
(c) both voltage and kVA rating are reduced in the same proportions as the frequency
(d) None of the above
(48) Repeated switching-in of transformer located near the generating stations may cause
(a) excessive temperature rise
(b) mechanical distortion of the windings and subsequent turn-to-turn insulation failure
(c) intense local eddy currents in the core
(d) surface flash-over of the bushings
(49) Dust should never be allowed to accumulate on the core and windings in a dry type transformer as it is likely to
(a) reduce dissipation of heat
(b) absorb oil and grease
(c) short circuit the windings
(d) corrode the metal surface
(50) Polarity test is performed to deterie
(a) no-load current
(b) the terminals having the same instantaneous polarity
(c) copper loss
(d) Efficiency
(51) Sumpner’s test is performed to measure
(a) Iron loss
(b) Copper loss
(c) Temperature rise
(d) Efficiency
(52) Usually short-circuit test is performed on
(a) LV side
(b) HV side
(c) Both the LV side and HV side
(d) None of the above
(53) Open-circuit test is also called as
(a) Impedance test
(b) Back-to-Back test
(c) Voltage ratio test
(d) No-load test
(54) While performing the open-circuit test the error due to power loss in ammeter can be eliminated by_____
(a) Short circuiting the ammeter while reading wattmeter
(b) Short circuiting the voltmeter while reading wattmeter
(c) Short circuiting the both ammeter and wattmeter
(d) Open circuit the wattmeter
(55) In a transformer the energy is conveyed from primary to secondary
(a) Through air
(b) By the flux
(c) Through cooling coil
(d) None of the above
(56) A buchholz relay can be installed on
(a) Welding transformers
(b) Air cooled transformers
(c) Auto transformer
(d) Oil cooled transformer
(57) The no-load current drawn by transformer is usually what percent of the full load current
(a) 0.2 to 0.5 percent
(b) 2 to 5 percent
(c) 12 to 15 percent
(d) 20 to 30 percent
(58) In a transformer routine efficiency depends upon ______
(a) Supply frequency
(b) Load current
(c) Power factor of load
(d) Both (a) and (b)
(59) The dielectric strength of transformer oil is expected to be
(a) 11 kV
(b) 33 kV
(c) 66 kV
(d) 132 kV
(60) Generator transformers are________
(a) Step-up transformer
(b) Step-down transformer
(c) Auto transformer
(d) Power transformer
