# All Day Efficiency of Transformer

- Link: https://studyelectrical.com/2016/09/all-day-energy-efficiency-transformer.html
- Published: 2016-09-19T19:30:00+00:00
- Author: 

**The ratio of output in kWh to the input in kWh of a transformer over a 24-hour
period is known as all day efficiency.**[⌊Three phase distribution transformer IMG 8096 Hurum Norway⌉](https://1.bp.blogspot.com/-qRbIs1fg8Ug/V-A1V2SUcJI/AAAAAAAACAU/aFOctED3b6g7IW_CFgqbpfmikZpOAC5vwCLcB/s1600/Three-phase_distribution_transformer_IMG_8096_Hurum_Norway.JPG)

The ordinary or commercial efficiency of a transformer is defined as the ratio of
output power to the input power.

Commercial efficiency = Output power ∕ Input power

## Importance of All Day Efficiency

There are certain [types of transformers](https://studyelectrical.com/2017/11/core-type-and-shell-type-transformers-comparison-application.html)
whose performance cannot be judged by commercial efficiency.

For instance, distribution transformers used for supplying lighting loads have their
primaries energized all the 24 hours in a day but the secondaries supply little 
or no load during the major portion of the day.

It means that a constant loss (i.e., iron loss) occurs during the whole day but 
copper loss occurs only when the transformer is loaded and would depend upon the
magnitude of load. 

Consequently, the copper loss varies considerably during the day and the commercial
efficiency of such transformers will vary from a low value (or even zero) to a high
value when the load is high.

The performance of such transformers is judged on the basis of energy consumption
during the whole day (i.e., 24 hours). This is known as all day efficiency or energy
efficiency.

## What is All day Efficiency?

**The ratio of output in kWh to the input in kWh of a transformer over a 24-hour
period is known as all day efficiency.**

ηall-day = kWh output in 24 hours ∕ kWh input in 24 hours

All day efficiency is of special importance for those transformers whose primaries
are never open-circuited but the secondaries carry little or no load much of the
time during the day.

In the design of such transformers, efforts should be made to reduce the iron losses
which continuously occur during the whole day.

_Note._ The efficiency of a transformer means commercial efficiency unless stated
otherwise.

> Read : [Percentage Impedance of Transformer](http://www.studyelectrical.com/2018/05/percentage-impedance-of-transformer-and.html)

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