Description : In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of?
Last Answer : In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of less than 15A.
Description : Material used for construction of transformer core is usually A. 0.4mm to 0.5 mm B. 4mm to 5 mm C. 14mm to 15 mm D. 25mm to 40 mm
Last Answer : d) 25mm to 40mm
Description : During short circuit test iron losses are negligible because A. The current on secondary side is negligible B. The voltage on secondary side does not vary C. The voltage applied on primary side is low D. Full-load current is not supplied to the transformer
Last Answer : C) the voltage applied on primary side is low
Description : 30 In performing the short circuit test of a transformer A. high voltage is usually short circuited B. low voltage side is usually short circuited C. any side is short circuited with preference D. none of the above
Last Answer : B. Low voltage side is usually short circuited
Description : How much is the no load current of transformer?
Last Answer : No load curent of transformer is 3 to 5% of rated current in transformer.
Description : What are two components of no load current in transformer?
Last Answer : i) IM (Magnetizing/reactive /wattless) current. It magnetizes core ii) Iw (Coreloss/ active/wattful ) current. It supplies hysteresis and eddy current loss and negligible I² R loss.
Description : What are the functions of no-load current in a transformer ?
Last Answer : No-load current produces flux and supplies iron loss and copper loss on no-load.
Description : 40 No load test on a transformer is carried out to find A. Copper loss B. magnetising current C. Magnetising current and loss D. Efficiency of the transformer
Last Answer : C. Magnetising current and loss
Description : 22 No load test on a transformer is carried out to find A. copper loss B. magnetising current C. Magnetising current and no load loss D. Efficiency of the transformer
Last Answer : C. Magnetising current and no load loss
Description : The inrush current of a transformer at no load is maximum if the supply voltage is switched on (1) at peak voltage value (2) at zero voltage value (3) at half voltage value (4) at 0.866 time voltage value
Last Answer : At 0.866 time voltage value
Last Answer : No-load current in a transformer lags behind the voltage by about 75°.
Last Answer : The no load current in a transformer lags behind the applied voltage by an angle of about 75°.
Last Answer : No-load current of a transformer has small magnitude and low power factor.
Description : The no-load current drawn by transformer is usually what per cent of the full-load current ?
Last Answer : 5 to 8 percentage of full load current
Description : Why the efficiency of distribution transformer is 60 to 70 % and not 100%?
Last Answer : Distribution transformer is designed for maximum efficiency at 60% to 70% load as it normally doesn't operate at full load all the time. Its load depends on distribution demand. Whereas power transformer ... efficiency at 100% load as it always runs at 100% load being near to generating station.
Last Answer : The magnetising current of a transformer is usually small because it has small air gap.
Description : In an actual transformer the iron loss remains practically constant from no load to full load because?
Last Answer : In an actual transformer the iron loss remains practically constant from no load to full load because core flux remains practically constant.
Description : 29.In transformer terminology, the ratio 20:1 indicates that A. there are 20 turns on primary one turn on secondary B. secondary voltage is 1/20th of the primary C. primary current is 20 times greater than the secondary current D. for every 0 turns on primary, there is one turn on secondary
Last Answer : A. there are 20 turns on primary one turn on secondary
Description : For a transformer, operating at constant load current, maximum efficiency will occur at?
Last Answer : For a transformer, operating at constant load current, maximum efficiency will occur at unity power factor.
Description : A 40 kVA transformer has a core loss of 400 W and a full load copper loss of 800 W. The proportion of full load at maximum efficiency is
Last Answer : A 40 kVA transformer has a core loss of 400 W and a full load copper loss of 800 W. The proportion of full load at maximum efficiency is 0.707
Description : A transformer operates 24 hours day at full -load. It's full -load efficiency is : (A) equal all day efficiency (B) more than all -day efficiency (C) less than all -day efficiency (D) equal to maximum efficiency
Last Answer : A transformer operates 24 hours day at full -load. It's full -load efficiency is : equal all day efficiency
Description : At full -load of a transformer, the iron loss and copper loss are 3000 W and 4000 W respectively. Then total loss at maximum efficiency is : (A) 7000 W (B) 6000 W (C) 8000 W (D) 4000 W
Last Answer : At full -load of a transformer, the iron loss and copper loss are 3000 W and 4000 W respectively. Then total loss at maximum efficiency is : 6000 W
Last Answer : The full-load copper loss of a trans¬former is 1600 W. At half-load, the copper loss will be 400 W.
Last Answer : In a power or distribution transformer about 10 percent end turns are heavily insulated to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns.
Description : A transformer at 25 Hz develops 20 W hysteresis loss and 50 W eddy current loss. If the applied voltage and frequency are doubled, the new core losses are (A) 140 W (B) 180 W (C) 240 W (D) 480 W
Last Answer : A transformer at 25 Hz develops 20 W hysteresis loss and 50 W eddy current loss. If the applied voltage and frequency are doubled, the new core losses are 240 W
Description : During No load why the power factor of the transformer is very low ?
Last Answer : Current flowing through the transformer consists of two components. Magnetizing current (Im) which is in quadrature (90 0 ) to the applied voltage and in phase current which is in phase to the applied voltage ... power factor of transformer during no load condition will by in the order of 0.1 to 0.2
Last Answer : A. Current flowing through the transformer consists of two components. Magnetizing current (Im) which is in quadrature (900) to the applied voltage and in phase current which is in phase to the applied voltage ... factor of transformer during no load condition will by in the order of 0.1 to 0.2
Description : A no-load test is performed on a transformer to determine?
Last Answer : A no-load test is performed on a transformer to determine magnetizing current and loss.
Last Answer : High Voltage side is open circuited.
Last Answer : Primary side is low voltage side and secondary side is high voltage side.
Description : 46 The core used in high frequency transformer is usually A. Copper core B. Cost iron core C. Air core D.Mid steel core
Last Answer : C. Air core
Description : The transformer ratings are usually expressed in terms of A. Volts B. Amperes C. kW D. kVA
Last Answer : D) KVA
Last Answer : The stator of phase shifting transformer for use in conjunction with an A.C. potentiometer usually has a two-phase winding.
Last Answer : The transformer ratings are usually expressed in terms of kVA.
Last Answer : Material used for construction of transformer core is usually silicon steel.
Last Answer : The thickness of laminations used in a transformer is usually 0.4 mm to 0.5 mm.
Last Answer : Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds 150°C.
Last Answer : The core used in high frequency transformer is usually air core .
Description : A 4000 kVA, 11 kV/132 kV delta-star connected 3-phase transformer has reactance, x1 = 0.12 p.u. The actual value of x1 referred to the low voltage side is (A) 0.85 Ω (B) 3.63 Ω (C) 36.3 Ω (D) 252 Ω
Last Answer : A 4000 kVA, 11 kV/132 kV delta-star connected 3-phase transformer has reactance, x1 = 0.12 p.u. The actual value of x1 referred to the low voltage side is 3.63 Ω
Description : 51 A transformer has negative voltage regulation when its load power factor is A. Zero B. Unity C. Leading D. Lagging
Last Answer : C. leading
Description : 6 In a two winding transformer, the primary and secondary induced emf E1 & E2 are always A. equal in magnitude B. anti phase with each other C. in phase with each other D. determined by load on transformer secondary
Last Answer : C. In phase with each other
Description : 10] The main reason for generation of harmonics in a transformer could be A. Fluctuating load B. Poor insulation C. Mechanical vibrations D. Saturation of core
Last Answer : D) saturation of core
Description : A transformer has negative voltage regulation when its load power factor is (1) Zero (2) Unity (3) Leading (4) Lagging
Last Answer : 0
Last Answer : An ideal transformer will have maximum efficiency at a load such that copper loss equal to iron loss.
Description : In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are?
Last Answer : In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are hysteresis and eddy current losses.
Description : The maximum load that a power transformer can carry is limited by its?
Last Answer : The maximum load that a power transformer can carry is limited by its voltage ratio.
Description : 27] In a transformer, the leakage flux of each winding is proportional to the current in that winding because A. Ohm's law applies to magnetic circuits B. Leakage paths do no saturate C. the two windings are electrically isolated D. mutual flux is confined to the core
Last Answer : B. Leakage path do not saturate
Description : The area of the yoke in a transformer is taken 15 to 20% larger than that of the core. Why?
Last Answer : By keeping yoke area 15-20% higher ,the flux density in the yoke is reduced, resulting into reduction in iron losses for yoke. The reduced core area results working flux density and needed to increase the number of turns.
Description : 12] Which is not the basic element of the transformer? A. core B. primary winding C. secondary winding D. mutual flux
Last Answer : D. Mutual flux