(i) Approximate voltage drop. When there is no-load on the transformer, then,
V1 = E1 (approximately).
and E2 = KE1 = KV1
Also E2 = 0V2, where 0V2 is secondary terminal voltage on no-loud
E2 = 0V2 =KV1
V2 = 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 I1Z02 = 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]
= I2R02 cos ɸ + I0X02 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:
(I2R02 cos ɸ – I2X02 sin ɸ)
- The approximate voltage drop for a transformer in general is given by :
(I2R02 cos ɸ ± I1X02 sin ɸ) … (12)
- The voltage drop as referred to primary is given by:
(I1R01 cos ɸ ± I1X02 sin ɸ
- Percentage voltage drop in secondary