Losses in Transformer

In this lecture, we will learn about the Losses in transformers in every detail with the equation where and when needed. So start by knowing the types of Losses in transformed and then we will discuss each in detail.

Losses in Transformer

An ideal transformer is loss-free. But in practice, there are some losses taking place in the transformer that we are going to discuss today.

Losses in a transformer refer to the energy dissipated as heat while transforming electrical energy from one voltage level to another. These losses can occur in various components of the transformer due to different factors.

As shown in the above figure, the losses in transformed is divided into two types:

Types of Losses in Transformer
1.	Copper Losses (Pcu)
2.	Iron Losses (Pi)

The Iron losses are further classified into two types:

1. Hysteresis loss in transformer
2. Eddy current loss in transformer

Now we will discuss losses in transformers one by one in detail.

Copper Loss In Transformer (P_cu)

The total power loss taking place in the winding resistances of a transformer is known as the copper loss.

\therefore Copper Loss = Power loss in the primary resistance + Power loss in the secondary resistance

The Copper loss is denoted by P_cu,

\therefore \;\boxed{\mathbf{P_{cu}= I_1^2 R_1 + I_2^2 R_2}}

Where, I_1^2 R_1 = Power loss taking place in the primary resistance R1

and I_2^2 R_2 = Power loss taking place in the primary resistance R2

The copper loss in the transformer should be kept as low as possible to increase the efficiency of the transformer. To reduce the copper loss, it is essential to reduce the resistance R1 and R2 of the primary and secondary windings.

Copper losses are also called variable losses as they are dependent on the square of load current. The relation between copper loss at full load and that of half load is as follows:

\mathbf{P_{cu(HL)} = \left(\frac{1}{2}\right)^2 P_{cu(FL)}}

\therefore \mathbf{P_{cu(HL)} = \frac{P_{cu(FL)}}{4}}

where P_{cu(HL)} = copper loss at half load and P_{cu(FL)} = copper loss at full load.

Iron Loss in Transformer (P_i)

Iron loss P_i is the power loss taking place in the iron core of the transformer.

There are two types of Iron loss in transformers:

Types of Iron Loss in Transformer
1.	Hysteresis Loss in Transformer
2.	Eddy current loss in Transformer

Iton loss is equal to the sum of two components called hysteresis loss and Eddy current loss.

P_i = Hysteresis Loss + Eddy current loss

Now we will study each component of Iron loss in detail.

Hysteresis Loss in Transformer

• The hysteresis loss is generally taking place in the magnetic material.

• The area enclosed by the hysteresis loop of a material represents the hysteresis loss.

• Hence special magnetic materials should be used in order to reduce the hysteresis loss.

• Material such as silicon steel has hysteresis loops with very small areas.

• Hence such materials are preferred for the construction of the core. Commercially such steel is called Logy, which means low hysteresis materials.

• The hysteresis loss is frequency-dependent. As we increase the frequency of operation, the hysteresis loss will increase proportionally.

Eddy current loss in Transformer

• Due to the time-varying flux, there is some induced EMF in the transformer core.

• This induced EMF causes some currents to flow through the core body. These currents are known as eddy current loss in transformers.

• The core is made of steel and has some finite resistance. hence due to the flow of eddy currents. heat will be produced. The power loss due to the eddy current is given by:

Eddy current loss = (Eddy Current)² x r

Where r = resistance of the core

• The eddy current losses are minimized by using the laminated core.

• The core is manufactured as a stack of laminations rather than a solid iron core.

• These laminations are insulated from each other by means of a varnish coating on all the laminations.

• Hence each lamination acts as a separate core with a small cross-sectional area, providing a large resistance to the flow of eddy currents.

• The eddy current loss is also frequency-dependent. It is directly proportional to the square of the operating frequency.

• Hence the iron loss P_i of the total loss is dependent on the frequency but the copper loss P_cu is constant irrespective of the frequency.

The iron loss is denoted by P_i, It is the sum of hysteresis and eddy current loss. Iron loss is a constant loss that does not depend on the level of load.

FAQs on Losses in Transformer

Also Read: Power Triangle: Understanding the Relationship Between Voltage, Current, and Power