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

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

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

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

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

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 : 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 : 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 : 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

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

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

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?

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?

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

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.

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

Answer : High voltage winding of the transformer has less cross-sectional area.

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

Answer : A shell-type transformer has reduced magnetic leakage.

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

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

Answer : Leading

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 single-phase transformer has no-load loss of 64 W, as obtained from an open circuit test. When a short-circuit test is performed on it with 90% of the rated currents flowing in its both LV and HV windings, ... .0% of the rated current (C) 80.0% of the rated current (D) 88.8% of the rated current

Answer : A single-phase transformer has no-load loss of 64 W, as obtained from an open circuit test. When a short-circuit test is performed on it with 90% of the rated currents flowing in its both ... measured loss is 81 W. The transformer has maximum efficiency when operated at 80.0% of the rated current

Description : Explain the effect of Harmonics on the Transformer.

Answer : Effect of Harmonics on the Transformer:  1. Core loss: Harmonic voltage increases the hysteresis and eddy current losses in the lamination. The amount of the core loss depends on ... small core vibrations.  5. Saturation problem: Sometimes additional harmonic voltage causes core saturation.

Description : List two special feature of welding transformer.

Answer : Special features of welding transformer: i) It is a step down transformer that reduces the source voltage to a voltage desired according to the demands of the welding process. ii) Having large primary turns and less ... V ii) Secondary voltage - 40 to 60 V iii) Secondary current - 200 to 600 A

Description : State two applications of isolation transformer

Answer : Applications of isolation transformer: i) Isolates the load equipment from supply ground: ii) Reduction of voltage spikes iii) It acts as a decoupling device. iv) Protects loads from harmonic distortion.

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%.

Description : Equivalent circuit of transformer

Answer : Equivalent Circuit Diagram of Transformer Referred to Primary: V1 -Primary Input voltage I1 - Input Current I0- Exciting current/ No load current Im- Magnetizing component ... equivalent of secondary terminal voltage ZL- Load impedance ZL ′- Primary equivalent of load impedance

Description : Single phase transformer

Answer : Single phase Transformer Transformer

Description : What is the use of transformer?

Answer : The use of transformer  is to do lower or raise  the voltage or currents in an electrical  circuit.  That's quite so simple. 

Description : Write about transformer on DC.

Answer : Transformer on DC : Transformer cannot work on DC. Transformer works on electromagnetic induction principle. Electromagnetic induction principle means when flux linking with coil changes and EMF induced in it ... winding insulation will burn. https://youtu.be/TVp_0fIfxqY

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.

Description : State any four characteristics of core type transformer.

Answer : Characteristics of core type transformer: i) It has one window. ii) It has one magnetic circuit. iii) Core surrounds the winding. iv) Average length of core is more. v) Area of cross ... Better cooling for winding. vii) Mechnical strength is comparatively less. viii) Repair and maintenance is easy.

Description : Explain construction and working of single phase Auto transformer.

Answer : Construction of single phase auto transformer: (i) It has only one winding wound on a laminated circular magnetic core. (ii) The core is made of silicon steel stampings. (iii) The two terminals of the ... help of handle. 5) The same transformer can be used as step-up or step down auto-transformer

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

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 : Primary winding of a transformer could either be a low voltage or high voltage winding.

Answer : The efficiency of a power transformer is of the order of 98 percent.

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

Answer : The maximum efficiency of a distribution transformer is at 50% full 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 : The power transformer is a constant main flux device.

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.

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