SOLUTION

Power transformers are designed to have maximum efficiency at full load.

Transformers of the large size used in generating stations at the sending end of the transmission line to step up the voltage and at the receiving end of the transmission line to step down the voltage is known as power transformers. A number of such transformers are connected in parallel. They are operated up to full-load capacity by connecting or disconnecting transformers depending upon the load condition. Power transformers are mostly used near full load conditions and hence designed for maximum efficiency at or near full load.

Power transformers are used for transmission as a step-up device hence they are not directly connected to consumers therefore, load fluctuation is very less. So the power transformer can operate on full load.

Distribution transformers are comparatively smaller transformers of rating of the order of hundreds of KVA and are connected directly to supply the load at 400/230 volts. Thus, the secondary side of a distribution transformer is directly connected to the load. They are to be kept in operation all the time for all the days irrespective of whether the consumer is utilizing the power or not. Thus, the load on a distribution transformer varies throughout the day depending upon how the consumers utilize the load. The average load on a distribution transformer is much less than its rated capacity. That is why they are rated to have maximum efficiency at a load lower than their full-load capacity. They are designed to have good all-day efficiency rather than the highest efficiency at or near full-load.