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Wednesday, 25 March 2020

Transformer Losses - Types of Losses in Transformer

Transformer Losses - Types of Losses in Transformer

Transformer Losses

The transformer has relatively low losses from all rotating AC machines with the same rating.

The efficiency of the distribution transformer is very high. Larger-sized units perform at more than 99%. 

While the performance of small units is more than 97%. The following losses occur in Transformers.

Eddy Current Losses 

Hysteresis Losses

1) core losses in transformer

    i)  Eddy Current Losses 
    ii) Hysteresis Losses

2) copper losses

Transformers have the highest losses in the two parts. One of these types of losses is called copper losses, which is located in the core of the transformer. Core losses occur when the transformer is connected to a supply voltage.

Since in practice the transformer is always connected to the rated voltage, That is why these accessions are considered permanent. These changes do not occur with load changes. But remember that applying less voltage reduces the amount of these losses.

The second type of loss occurs in the transformer winding. And Also change with load. Losses occurring in winding are called Copper Loses.

The following is an explanation of the losses occurring in the transformer.

Also Read: Transformer Basics and Parts of transformer

Core Losses in Transformer

The transformer core has Eddy Current Loses and Hysteres Loses. These losses are determined by a no-load test.

Eddy Current Losses

When the transformer is connected to the supply Voltage. So the alternating magnetizing flux in the core is Produced. which causes locally induced EMF. Due to the conductivity of core material and the close path a circulating current operates that called eddy current.

Eddy Current causes heat in the core. If heat volume exceeds a threshold, the core may burn. Eddy Current sets up his Flux. 

Which is opposite to the main flux or demagnetise the main flux? which causes losses. Cores are made of Petri-shaped to reduce eddy current losses.

We = K Bm2  f2 t2 ( watts)

 Ke = Eddy Current Constant, Depends on the conductivity of the material 

Bm = Maximum Flux Density in Wb/m2 

f     = Frequency of voltage in C/S

t     = The thickness of core lamination in meter

Hysteresis Losses

The direction of the magnetic flux changes after each half cycle in the Alternating current. Due to the molecular frictions of the core material the magnetic flux does not change very rapidly. Which causes losses called hysteresis losses.

In order to reduce losses, an appropriate amount of silicon is added to the steel. CRGO steel is commonly used for this purpose

Wh = Kh  Bm1.62  f   V (watts)

 Ke = Hysteresis Constant, Depends on the molecular frictions of the material 

Bm = Maximum Flux Density in Wb/m2 

F    = Frequency of voltage in C/S

V    = Voltage of core in m3

Copper Losses

Copper losses occur due to both primary and secondary winding resistances of the transformer. Copper losses vairy with the load. That is why they are called variable losses. Copper losses are tested through a short circuit test. 

Total Cu. Loss = I12R1 + I22R2 

Copper losses are directly proportional to the square of the current in the winding. That is why these losses are reduced by four times the square of the current if the current is half. And as the current is higher, these losses are increased by the square of the current.

Transformer rating VA is V and I multiplication. While the quantity of the V is almost constant.  copper Losses by the square of the current (I). Copper losses are therefore directly proportional to the square of the transformer's rating (KVA).

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