Electrical Engineering ⇒ Topic : Condition for Maximum Efficiency
Let us assume the iron losses = Pi
The total copper losses referred to the primary side =
In a given transformer, V1 is approximately constant and hence for a given value of /1 and cos Φ1 the efficiency will be maximum when the denominator of Eq. (1) is minimum. Thus, differentiating both the sides with respect to /1, we get
will be maximum when d/d/i = O.
Copper loss = Iron loss ............(2)
Hence, the efficiency of a transformer is maximum when the variable copper loss is equal to the constant iron loss. From Eq. (2), it follows that at maximum efficiency, the primary current
Similarly, at maximum efficiency, the load current
where Re2 is the equivalent resistance of the transformer referred to the secondary side given by Re2 = R2 + (V2/V1)2Ri [Eq.)]. The efficiency versus load current curves are shown in Fig. (a) for different power factors
FIGURE (a) Efficiency of a transformer as a function of the load current for different power factors
For a given transformer, the efficiency decreases with a decrease in power factor. Distribution transformers are generally designed to give maximum efficiency at 75% of full-load
CONDITION FOR MAXIMUM EFFICIENCY
It may be noted that the output current corresponding to maximum efficiency is given by
Figure (a) Efficiency vs current.
The plot of efficiency vs current is shown in Figure (a).
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