IMP VIVA QUESTIONS ON TRANSFORMER| CLASS 12TH

IMP VIVA QUESTIONS ON TRANSFORMER| CLASS 12TH

What Is A Transformer?

Ans.

A transformer is a static device which can transfer power from one circuit to another at same frequency.

How Does A Transformer Work?

Ans.

Transformer consists of two coils.If one coil is connected with ac voltage source then it will produce alternating flux in the core. Most of the flux is linked with second coil hence mutually induced emf will produce in the second coil as per faraday's law of electromagnetic induction.

 Explain the elementary theory of Ideal Transformer?

Ans.

 Ideal Transformer does not exist in real, only it help us to understand the basic concept of practical transformer. Under the following assumption Ideal Transformer can be treated as Practical Transformer.

·     The resistance of Transformer windings are Zero. Hence copper losses (I²R) are zero and windings are purely inductive.

·     Hysteresis losses & eddy current losses are zero.

·     There should be no losses

·The leakage flux should be zero

·     The permeability of core should be so high that the negligible current is required to  establish the flux in it.

Explain the working of tank and other accessories like terminal, bushing, conservator and breather?

Ans.

§  Tank:It filled with insulating oil which provide cooling to both winding and insulation to transformer assembly

§  Terminal and Bushing: The winding of transformer is brought outside and covered with the procelain bushings.

§  Conservator: It permits the expansion of oil and keep the main transformer full of oil. It is placed over tank.

§  Breather: It is placed over the conservator.It allow to pass the gasses in atmosphere which is produces in the tank. It consist of silica gel to prevent moisture enter inside the tank.

What Are The Various Types Of Transformers?

Ans.

Based on supply

o   Single phase transformer 

o   Three phase transformer 

Based on winding

o   Auto transformer (single winding)

o   Two winding transformer 

o   Three winding transformer 

o   Six winding transformer 

Based on construction 

o   Core Type transformer 

o   Shell Type transformer 

Based on the service

o   Distribution transformer 

o   Power transformer 

Based on measurement

o   Current transformer

o   potential transformer 

Based on cooling

o   Dry type Transformer

o   Oil immersed type transformer 

Based on function

o   Step up transformer 

o   Step down transformer

o   Isolation transformer

Explain Core type Transformer?

Ans.

It has a single magnetic core and two leg or limbs. First of all some part of low voltage winding (lv) is wound around the 2 limbs after that some part of high voltage (hv) winding is wound over lv winding.after that again lv is winding is wrapped over hv and so on. Both are wrapped over each other. Hence various section lv are connected in series and various section hv are also connected in series. Both are insulated by mica, paper etc.

Explain Shell type Transformer?

Ans. 

It has a double magnetic circuit and 3 limbs but winding will be wrapped around the central limb. First of all lv is wound around central limb then hv will wrapped then again lv and so on. In thus winding don’t overlap each other but they are of disc type. Hence hv is sand-witched between 2 lv winding.

Define Step up & Step down Transformer?

Ans. 

Step Up: This transformer is used to boost up the voltage level from primary winding to the secondary winding.
Step Down: This transformer is used to reduce the voltage level from primary winding to the secondary winding.

What Is Auto-transformer?

Ans.

In these transformer only one winding is used as primary and secondary. Also, primary and secondary are conductively coupled.

What Is Two Winding Transformer?

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Two separate windings one as primary and other as secondary are used. Both windings are magnetically coupled.

Define Transformation Ratio?

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 It is the ratio of sec. voltage to the primary voltage. Denoted by k.
For Ideal transformer: k = N2/N1 = V2/V1 = I1/I2

Can Dc Be Applied To Transformers ?

Ans.

No

1.  Transformer works on Faraday's law of Electromagnetic Induction for which current in coil must change. If DC is applied current will not change and transformer will not work.

2.  Practically winding resistance is very small. For DC ,inductive reactance is zero and frequency is zero. Therefore impedance is low. Thus winding draws more current which may damage the winding.

 What Is Three Winding Transformer?

Ans.

Three windings are used each work as primary and secondary. Also primary and secondary windings are conductively couple. They are three phase auto transformer.

 What Are Dry Type Transformer ?

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In this type of transformer, air is used as coolant.The heat is taken to walls of tank and dissipated to the surrounding air

Why the core of Transformer is laminated?

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To reduce eddy current loss. They are made up of thin laminated sheet & are insulated from each other. Finally the solid structure is pressed to remove presence of air gap.

Explain the effect of cooling?

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To control the temp. of transformer we use some cooling mechanism like cooling fins. It is attached with tank to prevent the harmful effect of excessive temp.

Explain auto and audio transformer?

Ans.

 It is smaller, lighter, cheaper as compare to dual winding transformer. In this single winding act as primary & sec. winding. It does not provide electrical isolation.

Why The Efficiency Of Distribution Transformer Is 60 To 70 % And Not 100%?

Ans.

Distribution transformer is designed for maximum efficiency at 60% to 70% load as it normally doesn’t operate at full load all the time. Its load depends on distribution demand. Whereas power transformer is designed for maximum efficiency at 100% load as it always runs at 100% load being near to generating station.

 Explain On The Material Used For Core Construction?

Ans.

The  core  is  constructed  by  sheet  steel  laminations  assembled  to  provide  a  continuous magnetic  path  with  minimum  of  air  gap  included.  The  steel  used  is  of  high  silicon content sometimes  heat  treated  to  produce  a  high  permeability  and  a  low  hysteresis  loss at  the  usual operating  flux  densities.  The  eddy  current  loss  is  minimized  by laminating  the  core,  the laminations being used from each other by light coat of coreplate varnish or by oxide layer on the surface. The thickness of lamination varies from 0.35mm for a frequency of 50Hz and 0.5mm for a frequency of 25Hz.

Why The Cross-section Of Iron Is Less Than Total Cross Section Area Of Core?

Ans.

This is because the core is laminated & on each lamination the insulations are are used.

What Is Hysteresis Loss In Transformer?

Ans.

The magneto motive force or mmf applied in the transformer core is alternating. For every cycle due to this domain reversal, there will be extra work done. For this reason, there will be a consumption of electrical energy which is known as Hysteresis loss of transformer.