There are 4 types of losses in a transformer i.e Core loss,Ohmic loss, Stray load loss and dielectric loss.
Lets understand each one by one in a easy way.
(1)Core losses in transformer :- Core losses have two components. The hysteresis loss Ph and the eddy current loss Pe .These together are
called no-load losses of a transformer and
are calculated by open circuit test.
i.e Core loss, Pc = Ph + Pe
(a)Hysteresis loss (Ph) in a transformer :- The hysteresis loss expression is given by
hysteresis loss, Ph =Kh f Bmx
where,
Kh = a proportionality
constant whose value depends upon the volume and quality of the core material
f = frequency of the power supply and hence frequency
of the alternating flux
Bm= maximum flux density in the core
x = called steinmetz’s constant and its varies from 1.5 to
2.5 and depends on the magnetic properties of the core material
By default, x=2 is taken as per new IEEE standards.
By default, x=2 is taken as per new IEEE standards.
Another expression for hysteresis loss can be obtain by
putting voltage equation,
V= √2 Ï€ f N BmAi
Or
Bm= V / √2Ï€fNAi
where,
V=voltage induced in the primary=supply voltage for an ideal
transformer
N=number of turns in primary, constant for a given transformer
Ai= net core area,constant for a given transformer
Putting Bmvalue in hysteresis loss, Ph =Kh f Bmx expression. We
get,
Ph =Ch f1-xVx
where, Ch = Kh/(√2Ï€NAi)x , is a
new constant
Thus you can see, hysteresis loss depends on supply
voltage and supply frequency.
How to reduce hysteresis losses in a transformer?
As proportionality constant Kh depends upon the quality of the core material therefore we must choose a
core material that has low Kh and high
permeability. usually silicon steel and Cold Rolled Grain Oriented steel are
used.
(b)Eddy current loss (Pe) in a transformer :- The eddy current loss formula is given by
eddy current loss, Pe =Ke f2 Bm2 t2
where,
Ke = proportionality
constant whose value depends upon the volume and resistivity of the core
material
t = thickness of the laminations
Another expression for eddy current loss can be obtain by
putting voltage equation, Bm= V / √2Ï€fNAi into eddy current loss expression
We get,
Pe =ke V2
where,
ke = a constant = Ke / (√2Ï€NAi)2
Hence, we see that eddy current loss of a transformer is
independent of frequency for a given supply voltage.
How to reduce eddy current losses in a transformer ?
As you saw, eddy current expression depends on Ke and thickness of the laminations t. Therefore, we must choose a core
material with high resistivity and also the thickness of the laminations
must be as small as possible.
(2)Ohmic losses in transformer :- The ohmic losses in transformer is due
to the winding resistance. So, whenever the transformer is loaded these losses occur as these losses depend on the current
through the windings.
Ohmic loss = I2R
Where,
I=current through windings
R=winding resistance
That is why when transformer is not loaded ohmic losses are negligible as the current through the windings is negligibly small
and this principle is used in open circuit test of a transformer which is used to
measure core losses in transformer.
As resistances vary with temperature therefore these losses also vary with temperature and must be calculated at standard operating
temperature.
How to reduce ohmic losses in transformer ?
Simple, use winding conductor of low
resistivity.
(3)Stray losses in transformers :- Always there exists some leakage flux in a transformer. This leakage
flux induces eddy currents in transformer tank, bolts, channels etc. .
This eddy current loss is called stray load loss of a transformer.
Leakage flux must be minimised to reduce it.
(4)Dielectric loss :- This loss occurs in the insulating materials i.e in the transformer oil and the solid insulation of high voltage transformers.
(4)Dielectric loss :- This loss occurs in the insulating materials i.e in the transformer oil and the solid insulation of high voltage transformers.
Its worth mentioning that transformers don’t have any mechanical losses as it is a static device and this makes transformer efficiency as high
as 99% , highest among all electrical machines.
This explains various losses in a transformer and how to reduce losses in transformer.
Closely related concepts :-
(1) Open circuit and Short Circuit test of transformer
(2) Transformer construction - shell type and core type transformer
(3) Transformer working principle
(4) Voltage regulation of transformer
(5) Efficiency of a Transformer
(6) Polarity test on Transformer
This explains various losses in a transformer and how to reduce losses in transformer.
Closely related concepts :-
(1) Open circuit and Short Circuit test of transformer
(2) Transformer construction - shell type and core type transformer
(3) Transformer working principle
(4) Voltage regulation of transformer
(5) Efficiency of a Transformer
(6) Polarity test on Transformer
