Rahul Tanwar Presentation 1 (P.T).

8/4/2019 Rahul Tanwar Presentation 1 (P.T).

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SUBMITTED BY:- RAHUL TANWAR

ELECTRICAL DEPT.

08EBNEE043

B-SET ,JAIPUR

SUBMITTED TO:-

PUSHPENDRA SINGH

H.O.D. ELECTRICAL DEPT.,

B.S.E.T, JAIPUR


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CONTENTS Introduction 1

Construction of P.T 3

Circuit diagram 5

Phasor diagram 7

High voltage P.T 8

Error in P.T 9

Reduction of error in P.T. 10

Characteristics of P.T. 11


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POTINTIAL TRANSFORMER

P.T. are used to operate voltmeters. The normal secondary voltage rating is 110v.

The P.T. may be considered as parallel transformer with

its secondary winding operating nearly under open circuit

conditions. The primary winding current in a P.T. certainly depends

upon the secondary circuit burden.

In a P.T. full line voltage is impressed upon its terminal.

Under normal operation the line voltage is nearly

constant and, therefore, the flux density and hence the

exciting current of a P.T. varies only over a restricted range


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POTINTIAL TRANSFORMERThe power loading of a P.T. is a

very small and consequently the

exciting current is of the sameorder as the secondary winding

current while in a power

transformer the exciting current is

a very small fraction of secondary

winding load current.


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Construction of P.T P.T. has larger core and conductor sizes.

The output of a P.T is always small and the size is quit

larger.

The temperature rise is small and hence there are nothermal problems caused by overloads as in power

transformer.

The load range from 2 to 3 times for low voltage P.T

and up to 30 or more times for same high voltage

transformer.


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Construction of P.T. CORE: The core may be of small or core type of

construction.

WINDINGS: The primary and secondary winding are

coaxial to reduce the leakage reactance to minimum.

INSULATION: Cotton tape and varnished cambric are used

as insulation for coil construction. Hard fiber separators

are used between coil.

BUSHINGS: Oil filled bushings are usually used for oil filledP.T as this minimizes the overall size of the transformer.


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Equivalent circuit of P.T


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Single phase P.T.


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Phasor diagram of a P.T


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High voltage P.T. Conventional type P.T used for high voltages of 100kv and

above, are very large in size and costly to build because of

insulation requirements.

Exe. A 110kv P.T has an overall height of about 7.5 metre

and weight nearly 5 tones.

Insulating casing:

Moulded rubber potential transformer: Cascaded transformers:


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Errors in P.T. Ratio (Voltage) error: The actual ratio of transformation varies

with operations and the errorin secondary voltage may be

defined as:

% Ratio error = Kn-R*100/R. Phase angle error: In an ideal voltage transformer there should

not be any phase difference between winding voltage and the

secondary winding voltage reversed. However, in an actual

transformer there exists a phase difference between Vp and Vsreversed.

Phase angle =(Is/n) *(Xicos - Risin) + (*Ie Xp Im Rp)/nVs.

= (Is/Vs)* (Xs cos - Rs sin)+(Ie Xp Im Rp)/nVs


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Reduction of errors in P.T. Reduction of magnetising and loss components: A

considerable improvement in the performance can be

made by reducing the value of Im and Ie. Such a reduction

requires short magnetic path, good quality core material,

low flux density in core and suitable precautions in the

assembly and interleaving of core.

Reduction of resistance and leakage reactance: Winding

resistance can be minimized by using thick conductors andby adopting the smallest length of mean turn.

Turn compensation: At no load the actual ratio exceeds

the turn ratio by an amount (IeRp+ImXp)/Vs.


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Characteristics of P.T Effect of secondary current or VA: If we increase the

secondary current is increased, and therefore, the primarycurrent increase.

Effect of power factor of secondary burden: If the powerfactor of secondary circuit burden is reduced, angle isincreased. This makes current Ip to shift toward currentIo. The voltage Vp and Vs come more nearly in to phase

with Ep and Es respectively since the voltage drop arealmost constant. The result is an increase in Vp relative toEp. But Vp is constant and, therefore , Ep reduce relativeto Vp.


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Characteristics of P.T. Effect of frequency: For a constant voltage, the flux is

inversely proportional to frequency. Increase in frequency

reduces the flux and, therefore, Im and Ie are decreased

and, therefore, the voltage ratio decrease.

Effect of primary voltage: There is no wide variation of

supply voltage to which the primary winding of the P.T. is

connected.


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REFERENCES

A.K Sawhney (2009), ISBN o-81-770-016-0.

EXTERNAL LINK http://en.wikipedia.org/Potential Transformer
http://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Transformer

Rahul Tanwar Presentation 1 (P.T).

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