Quantcast No-Load and Load Losses

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transformers have been placed in service in a test program to monitor long term performance of
the units on overhead distribution circuits. Westinghouse has present capacity for 2400 unit/year
in sizes 10 to 75 kVA and for primary voltages of 2.4 to 19.9 kV. Units for the typically larger
three-phase substation applications are not yet readily available, as the transformer manufacturers
are limited by the width of the amorphous steel material, as well as the quantity of material that is
available from the Allied Corporation, which has the patent on this material. There are presently
at least three manufacturers offering amorphous steel distribution type transformers for
commercial use.
3.2.2 Losses. A transformer has three distinct circuits; electric, magnetic, and dielectric.
Each of these circuits incurs losses, which may be subdivided as follows:
(a) Losses in the electric circuit.
o  I 2 R loss due to load currents.
o  I 2 R loss due to no-load exciting current.
o  Eddy-current loss in conductors due to leakage fields.
(b) Losses in magnetic circuit.
o
Hysteresis loss in core laminations.
o
Eddy-current loss in core laminations.
o
Stray eddy-current loss in core clamps, bolts, and other attachments.
(c) Loss in the dielectric circuit. This loss is small for all voltages up to 50 kV, and is
consequently included in the no-load losses.
3.2.2.1 No-Load and Load Losses. The various losses are normally grouped as follows:
(a) No-load losses (commonly called iron losses).
I 2 R loss due to no-load exciting current.
o
o
Hysteresis loss in core laminations.
o
Eddy-current loss in core laminations.
o
Stray eddy-current loss in core clamps, bolts and other attachments.
o
Loss in the dielectric circuit.
In practice only the hysteresis and eddy-current losses are of importance in transformers. These
losses are constant for a given applied voltage and unaffected by the load on the transformers.
The dielectric losses are also functions of the primary and secondary voltages, but vary slightly
with the temperature of the windings affected by the load on the transformer. The copper loss
due to the magnetizing current is generally negligible and is independent of the load for a given
3-3





 


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