Transformer Efficiency

Efficiency is an important parameter to consider when evaluating the performance of a transformer. It is defined as the ratio of output power to input power, expressed as a percentage. In other words, it represents the amount of power that is successfully transferred from the primary side to the secondary side of the transformer.

Efficiency at Full Load

Given that the transformer has a rating of 300 kVA, we can assume that at full load, it delivers 300 kVA of apparent power. The efficiency at full load is given as 95%. This means that the transformer is able to successfully transfer 95% of the input power to the load, while 5% is lost as losses (primarily copper and iron losses) within the transformer itself.

Efficiency at Half Load

At half load, the transformer delivers 150 kVA of apparent power. The efficiency at this load condition is given as 96%. This indicates that the transformer is able to transfer 96% of the input power to the load, while 4% is lost as losses within the transformer.

Maximum Efficiency at Unity Power Factor Load

To find the maximum efficiency at unity power factor (p.f.) load, we need to determine the load condition at which the efficiency is maximum. At unity power factor, the power delivered to the load is equal to the apparent power.

Let's assume that the transformer delivers P watts of real power at unity power factor. Since the power factor is unity, the apparent power is also P VA.

At unity power factor, the efficiency can be calculated as follows:

Efficiency = (Real Power Out / Real Power In) x 100

Since the real power delivered to the load is P watts and the input power is also P watts, the efficiency simplifies to:

Efficiency = (P / P) x 100 = 100%

Therefore, at unity power factor, the efficiency of the transformer is always 100%. This indicates that the transformer is able to transfer all the input power to the load at unity power factor, without any losses within the transformer itself.

Conclusion

The maximum efficiency at unity power factor load is always 100%, as there are no losses within the transformer itself at this load condition. Therefore, the given answer of "96.2%" is incorrect. The correct answer is 100%.