# A transformer cannot raise or lower the voltage of a D.C. supply because?

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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.

## Related questions

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Last Answer : If the supply frequency to the transformer is increased, the iron loss will increase.

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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.

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

Last 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.

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

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

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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.

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Description : A good voltage regulation of a transformer means?

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

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

Last 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.

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

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

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

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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.

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

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

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Description : The efficiency of a transformer, under heavy loads, is comparatively low because?

Last Answer : The efficiency of a transformer, under heavy loads, is comparatively low because copper loss becomes high in proportion to the output.

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Description : Explain the effect of Harmonics on the Transformer.

Last 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.

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Description : List two special feature of welding transformer.

Last 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

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Description : State two applications of isolation transformer

Last 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.

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

Last 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%.

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Description : Equivalent circuit of transformer

Last 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

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Description : Single phase transformer

Last Answer : Single phase Transformer Transformer

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Description : What is the use of transformer?

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

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Description : Write about transformer on DC.

Last 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

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

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Description : State any four characteristics of core type transformer.

Last 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.

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

Last 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

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

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

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

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

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

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

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Last Answer : The maximum efficiency of a distribution transformer is at 50% full load.

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

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

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Last Answer : The power transformer is a constant main flux device.

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

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

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

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

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

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Last Answer : Material used for construction of transformer core is usually silicon steel.

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

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Last 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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Last Answer : A transformer oil must be free from moisture.

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Last Answer : Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds 150°C.

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Last Answer : The main reason for generation of harmonics in a transformer could be saturation of core.

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Last Answer : Delta/star transformer works satisfactorily when on balanced as well as unbalanced loads.