Electrical Engineering - Transformer Losses and Efficiency test, Study notes of Electrical and Electronics Engineering

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Transformer Losses & Efficiency

and Test

Why Transformer

Rating in kVA?

Why Transformer Rating in kVA?

• (^) An important factor in the design and

operation of electrical machines is

• (^) The relation between the life of the insulation
• (^) operating temperature of the machine.
• (^) Therefore, temperature rise resulting

from the losses is a determining factor in

the rating of a machine.

Copper loss in a

transformer depends on

current and Iron loss

depends on voltage.

• What are the type of losses?

Transformer losses

and efficiency

• (^) There are broadly two sources of losses

in transformers on load.

• (^) Copper losses
• (^) Iron losses.

These losses appear in the form of heat and

produce

• (^) (i) an increase in temperature and
• (^) (ii) a drop in efficiency.

• (^) How we can say that…..
• (^) Copper loss in a transformer depends on current and Iron loss depends on voltage.

Copper Loss

• (^) Copper losses are variable and result in

a heating of the conductors, due to the

fact that they possess resistance.

• (^) If R

1 and^ R 2 are^ the^ primary^ and

secondary winding resistances then the

total copper loss is I 1

2

R 1 + I 2

2

R 2

Copper losses

Copper losses

• (^) It is clear that copper losses vary as the square of load current.
• (^) Thus if copper losses are 400 W at a load current of 10 A, then they will be (1/2)^2 x 400 = 100 W at a load current of 5A.
• Total losses in a transformer = Pi + PC = Constant losses + Variable losses
• (^) It may be noted that in a transformer, copper losses account for about 90% of the total losses.

Iron Loss

• (^) Iron Loss occurs in the magnetic core of the transformer. This is sum of hysteresis loss and eddy current loss.
• (^) Pi =Ph +Pe
• (^) The hysteresis and eddy current losses are given by

Iron Loss

• (^) As per given expressions Iron losses are constant for a given value of frequency and flux density.
• (^) Hysteresis loss is the heating of the core as a result of the internal molecular structure reversals which occur as the magnetic flux alternates.
• (^) The loss is proportional to the area of the hysteresis loop and thus low loss nickel iron alloys are used for the core since their hysteresis loops have small areas.

Iron Loss

• (^) The hysteresis and eddy current losses are given by
• (^) kh = proportionality constant which depends upon the volume and quality of the core material and the units used
• ke =. proportionality constant whose value depends upon the volume and resistivity of the core material, thickness of laminations and units used.

Iron Loss

• (^) These exponent constant can be represented by x is called Steinmetz constant.
• (^) Its value varies from 1.5 to 2.5, depending upon the magnetic properties of the core material.
• (^) The total core loss can be written as