Learn How To Calculate Transformer Losses And Efficiency

The transformer is an electric device that has a completely static structure, meaning it has no moving parts. It performs the crucial function of transferring electricity from one circuit to the other at a required frequency.

But do you know a considerable amount of power is lost in this transferring process?

Yes, you hear us right. 

What’s more notable is that these losses lead to the heating up of the transformer, which affects its efficiency. Therefore, it becomes important to calculate transformer losses to keep its efficiency under check.

Now you must be thinking, what are transformer losses, and why do they occur?

Don’t worry, we have got you covered!

In this blog, you will learn all the important aspects that relate to how you can calculate transformer losses. 

So, let’s dive in!

What is the Function of a Transformer?

Before we start with transformer losses, let’s understand how a transformer works.

You may have seen compact structures around your house in the electric power grid. These structures constantly convert high voltage power into low voltage to meet the requirements of different residential or commercial spaces.

It is important because most power grids supply 220 kV or 440 kV across different power stations. Such a high-power electric current can cause potential harm to various electronic devices. Therefore, transformers are used to step down the electric voltage for safe power consumption.

What are Transformer Losses?

To calculate transformer losses, it is vital to understand what these losses are.

As mentioned above, a transformer has no moving parts. There is no mechanical loss during the power distribution process. As a result, it has extremely high efficiency, above 90%. 

Then what is transformer loss?

The answer lies in the loss caused by load difference that occurs due to differences in the input and output voltage, which increases the temperature within the transformer structure.

When you calculate transformer losses, you will learn that these losses are categorised as core losses and copper losses. These losses are similar to other DC devices, except for zero mechanical loss.

4 Types of Transformer Losses

Now that you know the meaning of transformer losses, let’s explore another factor that is crucial to calculate transformer losses. Broadly, there are four types of transformer losses. These are explained below:

#1. Resistive Loss

In simple terms, this loss is known as copper loss, which is the result of the resistance of copper wire that is used for winding. This loss occurs because higher load frequency makes the electron move towards the outer surface of the conducting wire. The electrical fluctuations reduce the size of copper wire and increase resistive loss.

#2. Eddy Current Loss

Power loss in a transformer that is caused by currents created in the metal components is known as eddy current loss. Any conductor that is exposed to a moving magnetic field experiences induced voltage and current.  

#3. Hysteresis Loss

This loss occurs in a transformer due to remaining magnetism in the structure even when the magnetising force is removed. Magnetic parts are small sections of materials that act together when a magnetic force is applied. Due to this force, all the magnetic parts are realigned. The realignment process consumes power, which is used to calculate transformer losses. 

In simple terms, the movement of magnetic particles creates heat in the transformer, leading to hysteresis loss. 

#4. Flux Loss

When some of the flux lines from the primary can not pass through the core and to the secondary, a transformer gets flux loss, which results in a loss of electric current. 

There are two basic explanations for why flux lines move via the atmosphere rather than the core. These are:

  • – The iron core gets saturated, which prevents it from accepting any more flux lines. As a result, the lines of flux go through the air without being interrupted.
  • – Second, in the unsaturated area, the air and core normally have a reluctance ratio of 10,000:1. Accordingly, there is 1 line of flux via the air for every 10,000 lines of flux through the core. 

What is Transformer Efficiency?

Transformer efficiency is known as the ratio of its output to the input. To know the effects of voltage fluctuation when you calculate transformer losses, its efficiency is considered.

Generally, the efficiency is expressed in percentage. Moreover, the following formula is broadly applied for calculating the transformer’s efficiency:

= PoutPin


  • – represents the efficiency of the transformer.
  • – Pout is the transformer’s output power in watts.
  • – The Pin is the transformer’s input power in watts.

Can you Determine the Efficiency of a Transformer?

Now the question arises if it is possible to know the exact efficiency value once you calculate transformer losses.

To get the answer to this question, let’s consider the following situation.

A conventional transformer’s efficiency ranges from 96% to 99% and is generally very high. So, it is quite challenging to accurately measure the output and input of a transformer to assess its efficiency.

The main variance between output and input and output readings of machines is so negligible that a 15% range of instrument error will result in an error within the transformer wastes.


The transformer helps in the even distribution of power from the electric grid. Due to their static structure, there is hardly any damage to their mechanics. However, the fluctuation and difference in output and input voltage results in some loss. Therefore, to get its maximum benefit, it is important to calculate transformer losses. 


1. How many types of transformer losses are there?

Transformer losses are broadly categorised into the following four types:

  • – Flux loss
  • – Hysteresis loss
  • – Eddy current loss
  • – Resistive loss
2. What is the efficiency range of conventional transformers?

Generally, the efficiency of a conventional transformer ranges between 96% to 99%.

3. What is the most common reason for transformer loss?

The difference between input and output voltage creates heat in the transformer structure. This is the primary reason for transformer loss.