(i) **Approximate voltage drop**. When there is no-load on the transformer, then,

V_{1} = E_{1} (approximately).

and E_{2} = KE_{1} = KV_{1}

Also E_{2} = _{0}V_{2}, where _{0}V_{2} is secondary terminal voltage on no-loud

E_{2} = _{0}V_{2} =KV_{1}

V_{2} = secondary voltage on load.

Refer Fig. 32. The procedure of finding the approximate voltage drop of the transformer as referred to secondary is given below:

- Taking O as center, radius OC draw an arc cutting OA produced at E.

The total power voltage drop I_{1}Z_{02} = AC = AE which is approximately equal to AG.

- From B draw BF perpendicular on OA produced. Draw CG perpendicular to OE and draw BD parallel to OE.

Approximate voltage drop = AG = AF + FG = AF + BD [FG=BD]

= I_{2}R_{02} cos ɸ + I_{0}X_{02} sin ɸ

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

Figs. 33 and 34 refer to *unity *and *leading power factor *respectively.

- The approximate voltage drop for a
*leading power factor*becomes:

(I_{2}R_{02} cos ɸ – I_{2}X_{02} sin ɸ)

- The approximate voltage drop for a transformer
*in general*is given by :

(I_{2}R_{02} cos ɸ ± I_{1}X_{02} sin ɸ) … (12)

- The voltage drop as
*referred to primary*is given by:

(I_{1}R_{01} cos ɸ ± I_{1}X_{02} sin ɸ

*Percentage*voltage drop in*secondary*

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