Transformer-III.pptx

7/27/2019 Transformer-III.pptx

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Electric power from one circuit is transfer to electric power of same

frequency into another circuit.It can raise or lower the voltage in a circuit but with corresponding decrease

or increase in current.

Physical Basic is Mutual induction

The coil, in which electrical energy is fed from ac supply mains is known as

primary winding and coil from which energy is drawn out is known assecondary winding.

Working Principle of Transformer


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Core type Transformer


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Shell type Transformer


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Transformer 4

Transformer Construction


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1.The core type has two limbs & shell type has three

limbs.

2.Core type has longer mean length of iron core &

shorter mean length of coil turn.

Shell type has shorter mean length of iron core &

longer mean length of coil turn.

3.In core type transformers the LV(low voltage) coil

is wound next to the core & HV(high voltage) coil iswound on the LV coil after the insulation layer. In

Shell type transformers the LV & HV windings are

sandwiched between each other.

Difference between Core &

Shell type Transformer


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Transformer is a device which..


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Transformer Construction

Transformer consist of two coils having mutual

inductance and laminated steel core.

Two coils are insulated from each other and

laminated steel core.

Suitable container for assembly of core and

winding known as tank.

Suitable medium like oil for insulating the core

and its winding from container.


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Winding of transformer are made up ofinsulated copper wires. The cross-section of

wire will depends upon requirement ofcurrent carrying capacity and number of turnsis calculated according to voltage ratio ofprimary and secondary winding.

Heat produced in a transformer due to I2R inthe winding and hysteresis and eddy currentloss in the core.

I2R depends upon magnitude of currentflowing through the winding whentransformer is supplying some electrical load.


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The core loss which is sum of hysteresis and

eddy current loss remains constant at any

load.

As long as primary voltage is kept constant,

the core loss will remain constant loss.

I2R which is also called copper loss is a variableloss as it varies with the magnitude of current.


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Power Transformer and Distribution

Transformer

Power Transformer:

Connected at two ends of transmission line to step-up or step-down the voltage.

Rating- 11kv/220kv,100 MVA Distribution Transformer:

Feeds electricity to consumers

Rating: 11kv/400V

Energized for 24 hrs hence core losses of suchtransformer must be low to have betterefficiency.


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Theory of an Ideal TransformerAn ideal transformer is one that has

(i) no winding resistance

(ii) no leakage flux i.e., the same flux links both the windings

(iii) no iron losses (i.e., eddy current and hysteresis losses) in the

core


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Voltage Transformation Ratio (K)

We know,

Induced e.m.f in the primary winding is

Similarly Induced e.m.f in the secondary winding is

From the above equations of induced e.m.f.,


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Practical Transformer

A practical transformer differs from the ideal transformer in many respects.

The practical transformer has

(i) iron losses

(ii) winding resistances and(iii) magnetic leakage, giving rise to leakage reactance


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Practical Transformer

A practical transformer differs from the ideal transformerin many respects. The practical transformer has

(i) iron losses

(ii) winding resistances and

(iii) magnetic leakage, giving rise to leakage reactance


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Transformer on No Load with losses but no leakage reactance

We will consider two cases

1.When the Transformer is on No Load


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(i) The component IW in phase with the applied voltage V1. This is known

asactive or working or iron loss component and supplies the iron loss

and a very small primary copper loss.

(ii) The component Im lagging behind V1 by 90 and is known as

magnetizing component. It is this component which produces the

mutual flux f in the core.


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2.When the Transformer is on Load

T f i h i di i b i l k


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Transformer with winding resistance but no magnetic leakage


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Equivalent resistance


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Transformer with winding resistance with leakage reactance


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Equivalent Circuit of a Loaded Transformer


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Voltage Regulation

The voltage regulation of a transformer is the arithmetic difference between

the no-load secondary voltage (0V2) and the secondary voltage V2 on load

expressed as percentage of no-load voltage i.e.


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Losses in a Transformer(1) Core or Iron loss


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Applications of TransformersThere are four principal applications of transformers viz.

(i) power transformers (ii) distribution transformers

(iii) autotransformers (iv) instrument transformers

(i) Power Transformers. They are designed to operate with an almost constant

load which is equal to their rating. The maximum efficiency is designed to be at

full-load. This means that full-load winding copper losses must be equal to the

core losses.

(ii) Distribution Transformers. These transformers have variable load which is

usually considerably less than the full-load rating. Therefore, these are designedto have their maximum efficiency at between 1/2 and 3/4 of full load.

(iii) Autotransformers. An autotransformer has only one winding and is used in

cases where the ratio of transformation (K), either step-up or step down, differs

little from 1. For the same output and voltage ratio, an autotransformer requires

less copper than an ordinary 2-winding transformer. Autotransformers are usedfor starting induction motors (reducing applied voltage during starting) and in

boosters for raising the voltage of feeders.

(iv) Instrument transformers. Current and voltage transformers are used to

extend the range of a.c. instruments.

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Transformer-III.pptx