The power loss in transformer can be divided into two types namely the copper loss and the iron loss. The iron power loss in a transformer can be further classified into two types namely the hysteresis loss and eddy current loss.
 

Copper Power Loss in Transformer

 
The total losses that takes place in the winding resistance of a transformer is known as the copper loss. This loss in a transformer should be kept as low as possible to increases the efficiency of the transformer.
 
To reduce the copper loss, it is essential to reduce the resistance of primary and secondary windings of the transformer. It is also known as the variable loss as it is dependent on the square of load current.
 
To determine the copper loss, short circuit test on transformer is performed.
 

Iron Loss (Pi) in a Transformer

 
The power loss that takes place in its iron core is known as the iron loss. In the transformer, flux set up in the core remains constant from no load to full load. Hence this power loss in a transformer is independent of load and also known as constant losses of a transformer.
 
This power loss has two components named hysteresis loss and eddy current loss. To determine the iron loss, open circuit test of transformer is performed.
 

Hysteresis Power Loss in Transformer

 
The hysteresis loss of a magnetic material depends upon its area of the hysteresis loop. Hence the magnetic materials such as silicon steel, which has very small hysteresis loop area, are used for the construction of the core to minimize this power loss in a transformer.
 
The hysteresis loss (Ph = KhVfBm1.6) is frequency dependent. As we increase the frequency of operation, this loss increases proportionally.
 

Eddy Current Loss

 
Due to alternating flux in the transformer, some EMF is induced in the transformer core. This induced EMF causes some currents to flow through the core of the transformer. These currents are known as eddy currents. The core of transformer has some finite resistance. Hence due to the flow of eddy currents, some power loss takes place and it is known as eddy current loss
 
(Pe = KeVft2Bm2).
 
The eddy current loss is minimized by using the laminated core. These laminations are insulated each other by mean of a thin varnish coating. Hence each lamination acts as a separate core of a small cross sectional area, offers a high resistance to the flow of eddy currents.
 
Therefore, with the use of laminations in the core, eddy currents and eddy current losses are reduced. This power loss is also frequency dependent. It is directly proportional to the square of operating frequency.


Transformer — 7 | Objective Type Question Answers

#1 A current transformer is

magnetic component to change current level

#2 For power purpose sine wave shape is preferred because

it is stable wave shape as the line parameters cannot change it

#3 A sinusoidal e.m.f.

lags the flux inducing it by 90 degrees

#4 The advantage of putting tappings at the phase ends of a transformer is

to reduce the number of bushings

#5 In a three-phase delta transformer, one of the phases burns up. The transformer will supply

none of the above

#6 When a 440/220 V transformer is connected to 400 V D.C. supply

the transformer may burn

#7 Which of the following transformers is smallest ?

2 kVA 500 Hz

#8 The purpose of a breather in a transformer is to

extract moisture from the air

#9 Cross-over windings are used for

high voltage winding of small rating transformers

#10 In core type transformers, the concentric windings are used with

low  voltage winding placed next to core

#11 The yoke sections of transformers using hot-rolled laminations is made 15 percentage greater than that of the core to

to reduce the iron loss in yoke and magnetizing current

#12 When two single phase transformers are running in parallel and if the impedance triangles of the transformers are not identical in shape and size then

power factors at which the transformers operate will be different from one another and again these will be different from power factor of common load.

#13 What is the typical use of an auto-transformer ?

Variable transformer

#14 In a transformer the magnitude of mutual flux

same at all loads

#15 The principle of working of a transformer is

mutual induction

#16 In a transformer an insulating material may fail due to

any of the above

#17 The reactance of a transformer depends on ,

leakage  flux

#18 In a transformer on no load, the input voltage

leads the magnetizing current by 90 degrees

#19 The value of useful flux least depends on

load

#20 Which of the following can be reduced when the flux density In the transformer core is increased?

Size of the transformer

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