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Thursday, 20 August 2015

Losses in Transformer and Efficiency of Transformer

Losses in Transformer and Efficiency of Transformer Points : Losses in Transformer and Efficiency of Transformer, List of Losses in Transformer List of Losses in Transformer In a static transformer, there are no friction or winding Losses. Hence the only losses occurring are: 1) Core or Iron loss It includes both hyteresis loss and eddy current loss. Because the core flux in a transformer remains practically constant for all loads (it variation being 1 to 3% from no load to full-load), hence the core loss is practically the same at all loads.

Hysteresis loss Wn = n B16max fv Watts.
Eddy current loss Wo = P B2 max f2 t2 Watts.

These losses are minimized by using steel of high silicon content the core and by using very thin laminations.

Iron or core loss is found from the O.C. test. The input of the transformer when no-load measure the core loss.
(ii) Copper loss This loss is due to the ohmic resistances of the transformer windings. Total Cu loss = I2 RI + 122 R o2. It is clear that Cu loss is proportional to (current). Efficiency of Transformer The efficiency of a transformer at a particular load and power factor is defined as the out-put divided by the input the two being measured in the same units (either Watts or Kilowatts).

Efficiency = Output/Input

But a transformer being a highly efficient piece of equipment, has very small loss, hence it is impractical to try to measure transformer efficiency by measuring input and output. These quantities arc nearly of the same size. A better method is to determine the losses and then to calculate the efficiency from
It may be noted here that efficiency is based on power output in watts and not in volt-amperes, although losses are proportional to VA. Hence at any volt-ampere load, the efficiency depends on power factor, being maximum at a power factor of unity;

Efficiency can be computed by determining core loss from no-load or open-circuit test and Cu loss iron the short-circuit test.

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