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The core used in high frequency transformer is usually air core .

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

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

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

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

Description : Reduction in core losses and increase in permeability are obtained with transformer employing?

Answer : Reduction in core losses and increase in permeability are obtained with transformer employing core built-up of laminations of cold rolled grain oriented steel.

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 : 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 size of a transformer core will depend on?

Answer : The size of a transformer core will depend on frequency and area of the core.

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

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

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

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

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

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

Answer :  Sandwich type winding is used in 3 phase shell-type transformer.

Description : The core construction is like spokes of a wheel in following transformer:  (A) Berry Type Transformer (B) Core Type Transformer (C) Shell Type Transformer (D) None of the above

Answer : The core construction is like spokes of a wheel in following transformer:  Berry Type Transformer

Description : The main purpose of using core in a transformer is to (A) decrease iron losses (B) eliminate magnetic hysteresis (C) reduce reluctance of the common magnetic circuit (D) prevent eddy current loss

Answer : Reduce Relucatnce of the common magnetic circuit.

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 : The desirable properties of transformer core material are  (1) low permeability and low hysteresis loss. (2) high permeability and high hysteresis loss. (3) high permeability and low hysteresis loss. (4) low permeability and hysteresis loss.

Answer : The desirable properties of transformer core material are high permeability and low hysteresis loss.

Description : Why does the core of a transformer need to be laminated?

Answer : Transformer cores are laminated to reduce eddy current loss.

Answer : Transformer core is laminated to reduce Eddy current losses.

Answer : The stator of phase shifting transformer for use in conjunction with an A.C. potentiometer usually has a two-phase winding.

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

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

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 : 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 : 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.

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

Answer : The leakage flux in a transformer depends upon load current.

Answer : Noise level test in a transformer is a type test.

Answer : The value of flux involved in the e.m.f. equation of a transformer is maximum value.

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

Answer : The function of breather in a transformer is to arrest flow of moisture when outside air enters the transformer.

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 : 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 : In a transformer the resistance between its primary and secondary should be?

Answer : In a transformer the resistance between its primary and secondary should be infinity.

Description : If a transformer is continuously operated the maximum temperature rise will occur in?

Answer : If a transformer is continuously operated the maximum temperature rise will occur in windings.

Description : The hum in a transformer is mainly attributed to?

Answer : The hum in a transformer is mainly attributed to magnetostriction.

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 path of magnetic flux in a transformer should have?

Answer : The path of magnetic flux in a transformer should have low reluctance.

Description : what do not change in transformer?

Answer : Frequency and power are constant in transformers. Suppose we apply 50 Hz input frequency then the output frequency will also be 50 Hz whether the transformer is step up or step down. Similar ... is decreased on secondary side and hence power on primary side and secondary side remains constant.

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

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