## Total Approximate Voltage Drop of a Transformer

During the no-load condition, induced voltages at the primary and secondary windings are equal to the applied voltage and secondary terminal voltage respectively. If

_{0}V_{2}be the secondary terminal voltage at no load, we can write E_{2}=_{0}V_{2}.When the transformer is on no-load, then V

_{1}is approximately equal to E

_{1}. Hence E

_{2}= KE

_{1}= KV

_{1}.

Also,

E

E

_{2}=_{0}V_{2}where

_{0}V_{2}is the secondary terminal voltage on no-load,hence no-load secondary terminal voltage is KV

The secondary voltage on load is V

_{1}.The secondary voltage on load is V

_{2}. The difference between the two is I_{2}Z_{0}_{2}as shown in Figure below. The approximate voltage drop of the transformer as referred to secondary is found thus.With O as the centre and radius OC draw an arc cutting OA produced at M. The total voltage drop I

_{2}

Z

_{02}= AC = AM which is approximately equal to AN. From B draw BD perpendicular on OA produced.

Draw CN perpendicular to OM and draw BL parallel to OM.

Approximate voltage drop

= AN =AD+DN

= I

_{2}R

_{02}cosφ + I

_{2}X

_{02}sinφ

where φ

_{1}= φ

_{2}= φ (approx).

This is the value of the approximate voltage drop for a lagging power factor.

The different figures for unity and leading power factors are shown below.

The approximate voltage drop for the leading power factor becomes (I

In general, the approximate voltage drop is

_{2}R_{02}cosφ ± I_{2}X_{02}sinφ).In general, the approximate voltage drop is

(I

It may be noted that approximate voltage drop as referred to primary is=

(I

% voltage drop in the secondary is

_{2}R_{02}cosφ ± I_{2}X_{02}sin /φ).It may be noted that approximate voltage drop as referred to primary is=

(I

_{1}R_{01}cosφ ± I_{1}X_{01}sinφ)% voltage drop in the secondary is

=[(I

_{2}R_{02}cosφ ± I_{2}X_{02}sin /φ)/_{0}V_{2}]*100=[(100*I

=v_{2}R_{o2})/_{0}V_{2}]cosφ ±[(100*I_{2Xo}_{2})/_{0}V_{2}]sinφ_{r}cosφ ± v

_{x}sinφ

where,

v

_{r}=_{ }(100*I_{2}R_{o2})/_{0}V_{2 }=percentage resitive drop=(100*I_{1}R_{01})/V_{1}_{vx}=(100*I

_{2Xo}

_{2})/

_{0}V

_{2}=percentage reactive drop=(100*I

_{1}X

_{01})/V

_{1}

_{}

_{}

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