Saturday, January 9, 2016

Transformer Losses; Eddy current Hysteresis losses

Transformers are backbone of electrical systems. They are used for stepping up and stepping down the voltages.

We will study about losses in Transformer in this article. Losses are necessary evil in electrical systems. These losses can be minimized but could not be eliminated.
Transformers are static devices as they don’t have any rotary parts as these are static devices these don’t have any mechanical losses. Now there are only electrical losses which are needed to be looked upon.

There are various types of electrical losses in a Transformer, these are as below:-
1.    Core losses
2.    Copper losses

1.    Core losses:-
As clear from its name these losses occur in Transformers core and these consists of Hysteresis losses and eddy current losses. Hysteresis losses and eddy current losses both depends upon magnetic properties of Transformer core. These losses are always fixed and also known as no load losses and these don’t depend upon load current. These losses are also known as iron loss in Transformers.

Hysteresis Losses:-
How these losses are generated in Transformer is as explained below:-
Core of Transformer is made of CRGO Silicon Steel i.e. Cold rolled grain oriented Silicon Steel. As Steel is ferromagnetic material and ferromagnetic materials are very sensitive to magnetism. Now whenever magnetic flux passes through transformer core, core starts behaving like a magnet. As we know that magnetism is associated with domains. These domains are arranged in magnetic material in such a random manner so that resultant magnetic field of that material is zero. Whenever magnetic field is applied externally to that material these randomly oriented domains get aligned towards external mmf direction. When external mmf is removed maximum no. of domains come back to their random positions but till some domains still remains unchanged. To bring back these domains to their random position some external opposite mmf required to applied. The mmf applied to transformer to bring back domains in original position is alternating. This leads to electricity consumption and this is known as Hysteresis losses.

Eddy current losses:-
In Transformers power supply is applied to Transformer primary winding, this power supply which is alternating in nature produces alternating magnetic flux in the core, that flux links with secondary winding which will leads to induced voltage in secondary winding. Some of alternating flux also links with other parts of Transformer which are conducting in nature. These linkage fluxes will generate local induced EMF in these parts. This will leads to losses of energy as this will not contribute to Transformer output. So these losses are known as eddy current losses.

There are following formula uses to represent Hysteresis losses and eddy current losses:-

Hysteresis loss (Wh)= Kh X f X (Bm)1.6
Where Kh=Hysteresis Constant

These are measured in watts.
Now eddy current losses (We)= Ke X f2X K2fX(Bm)2
Where Ke= Eddy current constant
Kf= Form constant
From above relations we see that both Hysteresis losses and eddy current losses are independent of voltage and current. These losses are depend upon frequency and magnetic field strength as Hysteresis losses are directly proportional to system frequency and relation with magnetic field is as per equation.
Eddy current losses are proportional to square of both frequency and magnetic field strength.
2.    Copper losses:
Copper losses are the losses which occur in Transformer winding and these losses depend upon load current. These losses are also known as variable losses.
Copper losses are = I2R + Stray losses
Copper losses are also known Ohmic losses.