Short Answer:

Transformer efficiency tells us how well a transformer converts input electrical power into useful output power with minimum losses. A highly efficient transformer wastes very little energy as heat or other losses. It is usually expressed as a percentage and is an important performance parameter.

The efficiency of a transformer is calculated by comparing the output power to the input power. The formula is:
Efficiency (%) = (Output Power / Input Power) × 100.
In real applications, losses like iron loss and copper loss are considered while calculating efficiency.

Detailed Explanation:

Transformer efficiency and how it is calculated

Transformer efficiency refers to the ratio of useful power output delivered by the transformer to the total power input supplied to it. It gives a clear idea of how much power is being effectively transferred from the primary side to the secondary side, and how much is lost during the process. In an ideal transformer, efficiency would be 100%, but in practical transformers, there are always some losses. These losses reduce the efficiency slightly, though modern transformers are usually very efficient, often above 95%.

There are mainly two types of losses in a transformer:

1. Iron Loss or Core Loss:
   These are constant losses and occur due to magnetizing the iron core. They include:
   • Hysteresis Loss: Due to continuous magnetization and demagnetization of the core.
   • Eddy Current Loss: Circulating currents in the iron core cause this loss.
2. Copper Loss:
   These are variable losses and occur due to the resistance of the winding when current flows.
   • I²R Loss: When load current flows through primary and secondary windings, resistance causes heat loss.

Since core loss remains almost constant and copper loss varies with load, efficiency also changes slightly depending on loading conditions.

Efficiency Formula:

The basic efficiency formula is:
Efficiency (%) = (Output Power / Input Power) × 100

But since Input Power = Output Power + Losses, we can also write:
Efficiency (%) = (Output Power / (Output Power + Total Losses)) × 100

Where:

• Output Power = V₂ × I₂ × power factor
• Total Losses = Iron loss + Copper loss

Condition for Maximum Efficiency:

The transformer gives maximum efficiency when copper loss is equal to iron loss.
That is:
Iron Loss = Copper Loss
This condition is used while designing the transformer to ensure it operates efficiently at the desired load level.

Typical Values and Importance:

• Most distribution transformers have an efficiency of 95% to 99%.
• Higher efficiency reduces energy loss and heat generation.
• It saves operational cost and increases the reliability of power supply.
• In critical applications like hospitals, industries, and data centers, high efficiency is essential.

Conclusion:

Transformer efficiency shows how effectively a transformer delivers output power compared to the input power. It is reduced due to losses in the core and windings. The efficiency is calculated using the formula: (Output/Input) × 100, and is highest when copper loss equals iron loss. Good transformer efficiency ensures energy savings, stable performance, and reliable power delivery in all electrical systems.