The function of oil in a transformer is to provide

The function of oil in a transformer is to provide 

A) Insulation and cooling B) Protection against Lightning C) Protection against short circuit D) Lubrication
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1 Answer

Answer :

The function of oil in a transformer is to provide Insulation and cooling

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Transformer oil tester is used to know

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A transformer oil must be free from?

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

Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds?

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

The dielectric strength of transformer oil is expected to be?

Description : The dielectric strength of transformer oil is expected to be?

Last Answer : The dielectric strength of transformer oil is expected to be 33 kV.

The function of conservator in a transformer is?

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.

The function of breather in a transformer is?

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

Explain direct loading test on single phase transformer with neat circuit diagram.

Description : Explain direct loading test on single phase transformer with neat circuit diagram. 

Last Answer : Direct loading test on single phase transformer with neat circuit diagram:   Direct loading test on transformer is carried out to calculate the losses, efficiency and voltage regulation of the ... voltage.  Efficiency and regulation can be calculated by using following formulae:   

Explain the effect of Harmonics on the Transformer.

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.

List two special feature of welding transformer.

Description : List two special feature of welding transformer.

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State two applications of isolation transformer

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.

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

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%.

Equivalent circuit of transformer

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

Single phase transformer

Description : Single phase transformer

Last Answer : Single phase Transformer Transformer

What is the use of transformer?

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. 

Transformer on DC

Description : Write about transformer on DC.

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Why phasing out and polarity test is carried out on three phase transformer?

Description : Why phasing out and polarity test is carried out on three phase transformer?

Last Answer : The phasing out test is carried out to identify the windings (primary and secondary) of corresponding phase of the three phase transformer. The polarity test is carried out to identify the ... identical polarity of the primary and secondary windings of each phase of the three phase transformer.

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

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.

State any four characteristics of core type transformer.

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.

Explain construction and working of single phase Auto transformer.

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

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If the frequency of input voltage of a transformer is increased keeping the magnitude of voltage unchanged,

Description :  If the frequency of input voltage of a transformer is increased keeping the magnitude of voltage unchanged, then: A) both hysteresis loss and eddy current loss in the core will increase B) ... current loss will increase D) hysteresis loss will decrease but eddy current loss will remain unchanged

Last Answer :  If the frequency of input voltage of a transformer is increased keeping the magnitude of voltage unchanged, then: hysteresis loss will decrease but eddy current loss will remain unchanged

Full load copper loss in a transformer is 1600 watts. At half load the copper loss will be:

Description : Full load copper loss in a transformer is 1600 watts. At half load the copper loss will be: A) 6400 watt B) 1600 watt C) 800 watt D) 400 watt

Last Answer :  Full load cupper loss in a transformer is 1600 watts. At half load the cupper loss will be: 400 watt

The current transformer that is used to measure a 100 A current by 5 A ammeter is a_____.

Description : The current transformer that is used to measure a 100 A current by 5 A ammeter is a_____.

Last Answer : The current transformer that is used to measure a 100 A current by 5 A ammeter is a step up transformer

The voltage applied to the H.V. side of a transformer during S.C. test is 2% of the rated voltage. The core loss

Description : The voltage applied to the H.V. side of a transformer during S.C. test is 2% of the rated voltage. The core loss as the fraction of its rated core loss is (a) 4% (b) 0.4% (c) 0.25% (d) 0.04%

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Three phase step-up transformer installed at power house, just before commencement of transmission line, have:

Description : Three phase step-up transformer installed at power house, just before commencement of transmission line, have:

Last Answer : Three phase step-up transformer installed at power house, just before commencement of transmission line, have: star delta connections

When two transformer of different kVA rating are connected in parallel they share the load in proportion to

Description : When two transformer of different kVA rating are connected in parallel they share the load in proportion to their respective kVA rating only when their:

Last Answer : When two transformer of different kVA rating are connected in parallel they share the load in proportion to their respective kVA rating only when their: P u impedance are equal

In a transformer the voltage regulation will be zero when it operates at

Description : In a transformer the voltage regulation will be zero when it operates at (A) unity p.f. (B) leading p.f. (C) lagging p.f. D) zero p.f. leading.

Last Answer : In a transformer the voltage regulation will be zero when it operates at leading p.f.

The primary winding of a 220/6 V, 50 Hz transformer is energised from 110 V, 60 Hz supply. The secondary

Description : The primary winding of a 220/6 V, 50 Hz transformer is energised from 110 V, 60 Hz supply. The secondary output voltage will be (A) 3.6 V. (B) 2.5 V. (C) 3.0 V. (D) 6.0 V.

Last Answer : The primary winding of a 220/6 V, 50 Hz transformer is energised from 110 V, 60 Hz supply. The secondary output voltage will be 3.0 V.

The core flux of a practical transformer with a resistive load

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A single-phase transformer has a turns ratio of 1 :2 and is connected to a purely resistive load as shown in the

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A simple phase transformer has a maximum efficiency of 90% at full load and unity power factor. Efficiency at

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A 500 kVA, 3-phase transformer has iron losses of 300 W and full load copper losses of 600 W. The percentage

Description : A 500 kVA, 3-phase transformer has iron losses of 300 W and full load copper losses of 600 W. The percentage load at which the transformer is expected to have maximum efficiency is  (A) 50.0% (B) 70.7% (C) 141.4% (D) 200.0%

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Which three-phase connection can be used in a transformer to introduce a phase difference of

Description : Which three-phase connection can be used in a transformer to introduce a phase difference of 30o between its output and corresponding input line voltages  (A) Star-Star (B) Star-Delta (C) Delta-Delta (D) Delta-Zigzag

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A single-phase, 50 kVA, 250 V/500 V two winding transformer has an efficiency of 95% at full load, unity

Description : A single-phase, 50 kVA, 250 V/500 V two winding transformer has an efficiency of 95% at full load, unity power factor. If it is re-configured as a 500 V/750 V auto-transformer, its efficiency at its new rated load at unity power factor will be  (A) 95.752% (B) 97.851% (C) 98.276% (D) 99.241%

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A single-phase transformer has no-load loss of 64 W, as obtained from an open circuit test. When a short-circuit

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

Last 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

Which losses in a transformer varies significantly with load

Description : Which losses in a transformer varies significantly with load  a. Hysteresis losses b. Eddy current losses c. Copper losses d. Core losses 

Last Answer : Which losses in a transformer varies significantly with load Copper losses

For a pulse transformer, the material used for its core and the possible turn ration from primary to secondary

Description : For a pulse transformer, the material used for its core and the possible turn ration from primary to secondary are respectively   (A) ferrite : 20 : 1 (B) laminated iron : 1 :1 (C) ferrite : 1 : 1 (D) powered iron : 1: 1

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The transformer utilization factor of full wave bridge rectifier is

Description : The transformer utilization factor of full wave bridge rectifier is   (A) 0.812 (B) 0.286 (C) 0.693 (D) 0.782

Last Answer : The transformer utilization factor of full wave bridge rectifier is 0.286 

In a power transformer, the fundamental frequency of the hum arising due to magnetostriction is

Description : In a power transformer, the fundamental frequency of the hum arising due to magnetostriction is  (a) equal to the line frequency (b) double the line frequency (c) 4 times the line frequency (d) not related to the line frequency

Last Answer : In a power transformer, the fundamental frequency of the hum arising due to magnetostriction is double the line frequency

A transformer is used to

Description : A transformer is used to

Last Answer : A transformer is used to Step-up or step-down AC voltage

If the secondary turns of a transformer are doubled and at the same time primary voltage is

Description : If the secondary turns of a transformer are doubled and at the same time primary voltage is reduced to half then the secondary voltage will

Last Answer : If the secondary turns of a transformer are doubled and at the same time primary voltage is reduced to half then the secondary voltage will not change

In a step-up or step-down transformer, electrical power is transferred from one circuit to another without change in

Description : In a step-up or step-down transformer, electrical power is transferred from one circuit to another without change in

Last Answer : In a step-up or step-down transformer, electrical power is transferred from one circuit to another without change in frequency

Which of the following is not a basic element of a transformer ?

Description : Which of the following is not a basic element of a transformer ?  1. Core 2. Primary winding 3. Secondary winding 4. Mutual flux 

Last Answer : A

A transformer transforms

Description : A transformer transforms  1. Frequency 2. Voltage 3. Current 4. Voltage and current

Last Answer : A transformer transforms Voltage and current

The hysteresis and eddy current losses of a single phase transformer working on 200 V, 50 Hz

Description : The hysteresis and eddy current losses of a single phase transformer working on 200 V, 50 Hz supply are Ph and Pe respectively. The percentage decrease in these when operated on a 160 V, 40 Hz supply are   (a) 32, 36 (b) 20, 36 (c) 25, 50 (d) 40, 80 

Last Answer : The hysteresis and eddy current losses of a single phase transformer working on 200 V, 50 Hz supply are Ph and Pe respectively. The percentage decrease in these when operated on a 160 V, 40 Hz supply are 20, 36

For a constant load current, transformer maximum efficiency occurs at

Description : For a constant load current, transformer maximum efficiency occurs at   (a) any power factor (b) zero power factor leading (c) zero power factor lagging (d) unity power factor 

Last Answer : For a constant load current, transformer maximum efficiency occurs at unity power factor 

In a transformer, low voltage winding is placed near the core in case of concentric windings so

Description : In a transformer, low voltage winding is placed near the core in case of concentric windings so as to  1. Reduce the leakage flux 2. Reduce the insulation requirement 3. Reduce the risk of voltage shock in case of insulation breakdown 4. Reduce the ... a) 1, 2, 3 (b) 2, 3, 4 (c) 1, 2, 3, 4 (d) 2, 3

Last Answer : In a transformer, low voltage winding is placed near the core in case of concentric windings so as to  1. Reduce the leakage flux 2. Reduce the insulation requirement 3. Reduce the risk of voltage shock in case of insulation breakdown 4. Reduce ... ) 1, 2, 3 (b) 2, 3, 4 (c) 1, 2, 3, 4 (d) 2, 3

In a transformer, zero voltage regulation at full load is

Description : In a transformer, zero voltage regulation at full load is   (a)Not possible   (b) Possible at unity power factor load   (c) Possible at leading power factor load   (d) Possible at lagging power factor load

Last Answer : In a transformer, zero voltage regulation at full load is Possible at leading power factor load 

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

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

The degree of mechanical vibrations produced by the laminations of a transformer depends on?

Description : The degree of mechanical vibrations produced by the laminations of a transformer depends on?

Last Answer : The degree of mechanical vibrations produced by the laminations of a transformer depends on tightness of clamping, gauge of laminations, size of laminations.

A transformer core is laminated to?

Description : A transformer core is laminated to?

Last Answer : A transformer core is laminated to reduce eddy current losses.