Standard KVA Rating of Three Phase Power Transformer

Rated kVA

• The rated kVA is related to the product of rated voltage, rated current and appropriate phase factor as given below.

Number of Phases	Phase Factor
1	1
3	1.73

• The rated kVA corresponding to continuous duty, if it is oil immersed transformer considering the standard for overload as per Indian standard.
• The occasional overload up to 1.5 times the rated value may be allowed on transformer with rated power up to 100 MVA and in this condition no limitations by bushings, tap changers or any other auxiliaries shall apply.
• Daily overload / emergency overload in excess of 1.5 times may be restricted by considering performance of auxiliaries. 
• The operation of transformer at 1.5 times the rated current  may affect the transformer life 3% without making tap changes.

The standard kVA rating for three phase power transformer is given as below

kVA rating

5	80
6.3	100
8	125
10	160
12.5	200
16	250
20	315
25	400
31.5	500
40	630
50	800
63	250
	315

Bold figures are preferred rating of Power Transformer

• The rating of three single phase transformer intended for use of three phase transformer is one third that of kVA rating of three phase transformer.

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