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The no load current in a transformer lags behind the applied voltage by an angle of about 75°.

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Description : In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are?

Answer : In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are hysteresis and eddy current losses.

Answer : No-load current in a transformer lags behind the voltage by about 75°.

Description : Even at no-load, a transformer draws current from the mains. Why?

Answer : No-load current of a transformer has small magnitude and low power factor.

Answer : In an actual transformer the iron loss remains practically constant from no load to full load because core flux remains practically constant.

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

Answer : At 0.866 time voltage value

Description : A no-load test is performed on a transformer to determine?

Answer : A no-load test is performed on a transformer to determine magnetizing current and loss.

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?

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 : For a transformer, operating at constant load current, maximum efficiency will occur at?

Answer : For a transformer, operating at constant load current, maximum efficiency will occur at unity power factor.

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

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

Answer : An ideal transformer will have maximum efficiency at a load such that copper loss equal to iron loss.

Description : The maximum load that a power transformer can carry is limited by its?

Answer : The maximum load that a power transformer can carry is limited by its voltage ratio.

Answer : The full-load copper loss of a trans¬former is 1600 W. At half-load, the copper loss will be 400 W.

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 : State and justify which of the following two transformers is better:  Transformer A = 4% voltage regulation  Transformer B = 6% voltage regulation

Answer : Transformer A with 4% voltage regulation is better.  Justification: Voltage regulation refers to the percentage change in secondary voltage when load is changed from no-load to full-load with primary voltage ... 4% voltage regulation, which is less as compared to 6% of transformer B, it is better.

Answer : A transformer cannot raise or lower the voltage of a D.C. supply because Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero.

Answer : When a given transformer is run at its rated voltage but reduced frequency, its core flux density is increased.

Description : A good voltage regulation of a transformer means?

Answer : A good voltage regulation of a transformer means output voltage fluctuation from no load to full load is least.

Description : The voltage transformation ratio of a transformer is equal to the ratio of?

Answer : The voltage transformation ratio of a transformer is equal to the ratio of secondary induced e.m.f. to primary induced e.m.f.

Description : If a transformer is switched on to a voltage more than the rated voltage?

Answer : If a transformer is switched on to a voltage more than the rated voltage its power factor will deteriorate.

Answer : The magnetising current of a transformer is usually small because it has small air gap.

Description : When secondary of a current transformer is open-circuited its iron core will be?

Answer : When secondary of a current transformer is open-circuited its iron core will be hot because of heavy iron losses taking place in it due to high flux density.

Description : The secondary of a current transformer is always short-circuited under operating conditions because it?

Answer : The secondary of a current transformer is always short-circuited under operating conditions because it avoids core saturation and high voltage induction.

Description :  The no-load current drawn by transformer is usually what per cent of the full-load current ?

Answer : 5 to 8 percentage of full load current

Description : A transformer has negative voltage regulation when its load power factor is   (1) Zero (2) Unity (3) Leading (4) Lagging

Answer : Leading

Description :  An AC supply of 230 V is applied to a half-wave rectifier circuit through a transformer having primary to secondary turn’s ratio 12:1. The peak inverse voltage is A) 8.62 V B) 12 V C) 19.17 V D) 27.11 V 

Answer :  An AC supply of 230 V is applied to a half-wave rectifier circuit through a transformer having primary to secondary turn’s ratio 12:1. The peak inverse voltage is A) 8.62 V B) 12 V C) 19.17 V D) 27.11 V 

Answer : The purpose of providing an iron core in a transformer is to decrease the reluctance of the magnetic path.

Description : State why a transformer always have an efficiency of more than 90%.

Answer : As transformer is static device with no moving parts, the losses due to friction & windage are completely absent. Hence transformer has efficiency of more than 90%.

Answer : An ideal transformer has infinite values of primary and secondary inductances. The statement is false.

Answer : An ideal transformer is one which has no losses and magnetic leakage.

Description : An open-circuit test on a transformer is conducted primarily to measure?

Answer : The open-circuit test in a transformer is used to measure

Description : The changes in the volume of transformer cooling oil due to the variation of atmospheric temperature during day and night is taken care of by which part of the transformer?

Answer : The changes in the volume of transformer cooling oil due to the variation of atmospheric temperature during day and night is taken care of by conservator.

Answer : Iron loss of a transformer can be measured by low power factor wattmeter.

Answer : The transformer laminations are insulated from each other by thin coat of varnish.

Description : The noise produced by a transformer is termed as?

Answer : The noise produced by a transformer is termed as hum.

Description : Step-down transformer converts high voltage and low current into:  (A) How voltage and high current (B) High voltage and low current (C) Low voltage and high current (D) None of the above

Answer : Step-down transformer converts high voltage and low current into: Low voltage and high current

Description : The kVA rating of Three-phase transformer with Voltage = 200V and Current = 100A will be :  (A) 34.64 kVA (B) 75 kVA (C) 20 kVA (D) None of the above

Answer : The kVA rating of Three-phase transformer with Voltage = 200V and Current = 100A will be : 34.64 kVA

Answer : In the transformer low voltage winding has got more cross-sectional area.

Answer : High voltage winding in a transformer has more number of turns.

Answer : In a transformer, routine efficiency depends upon load current and power factor of load.

Answer : Transformer breaths in when load on it decreases.

Answer : The purpose of providing iron core in a step-up transformer is to decrease the magnitude of magnetizing current.

Answer : In a transformer, the tappings are generally provided on low voltage side.

Answer : The use of higher flux density in the transformer design reduces weight per kVA.

Answer : The chemical used in breather for transformer should have the quality of cleansing the transformer oil.

Answer : The transformer ratings are usually expressed in terms of kVA.

Answer : The thickness of laminations used in a transformer is usually 0.4 mm to 0.5 mm.

Answer : conservator or a reservoir tank for insulating oil in transformer which used for balanced the onload oil level with help of oil level indicator which mount on middle part of reservoir tank.

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