Definition: All day efficiency means the power consumed by the transformer throughout the day. It is defined as the ratio of output power to the input power in kWh or wh of the transformer over 24 hours. Mathematically, it is represented as
All day efficiency of the transformer depends on their load cycle. The load cycle of the transformer means the repetitions of load on it for a specific period.
The ordinary or commercial efficiency of a transformer define as the ratio of the output power to the input power.
What is the need of All Day Efficiency?
Some transformer efficiency cannot be judged by simple commercial efficiency as the load on certain transformer fluctuate throughout the day. For example, the distribution transformers are energised for 24 hours, but they deliver very light loads for the major portion of the day, and they do not supply rated or full load, and most of the time the distribution transformer has 50 to 75% load on it.
As we know, there are various losses in the transformer such as iron and copper loss. The iron loss takes place in the core of the transformer. Thus, the iron or core loss occurs for the whole day in the distribution transformer.The second type of loss known as copper loss takes place in the windings of the transformer also known as the variable loss. It occurs only when the transformers are in the loaded condition.
Hence, the performance of such transformers cannot be judged by the commercial or ordinary efficiency, but the efficiency is calculated or judged by All Day Efficiency also known as operational efficiency or energy efficiency which is computed by energy consumed during 24 hours.