Transformers - kVA Ratings vs. Volt and Amps

Reference tables for single-phase and three-phase transformer full load currents based on kVA ratings and voltage levels. Includes transformer principles and calculation examples.

Transformers - kVA Ratings vs. Volt and Amps

A transformer transfers electrical energy from one circuit to another through inductively coupled conductors. For an ideal transformer:

U1 / U2 = N1 / N2 = I2 / I1

Where:

U = electrical potential difference (Voltage)
N = number of turns of wire
I = current (Amps)

Example

A transformer with 500 primary turns, 3000 secondary turns and 230 V primary voltage:

U2 = U1 × N2 / N1 = 230 × 3000 / 500 = 1380 V = 1.38 kV

kVA Rating	120 V (A)	240 V (A)	480 V (A)
0.05	0.42	0.21	0.1
0.075	0.63	0.31	0.16
0.1	0.83	0.42	0.21
0.15	1.25	0.63	0.31
0.25	2.08	1.04	0.52
0.5	4.17	2.08	1.04
0.75	6.25	3.13	1.56
1	8.33	4.17	2.08
1.5	12.5	6.25	3.13
2	16.7	8.33	4.17
3	25	12.5	6.3
5	41.7	20.8	10.4
7.5	62.5	31.3	15.6
10	83.3	41.7	20.8
15	125	62.5	31.3
25	208	104.2	52.1
37.5	313	156.3	78.1
50	417	208.3	104.2
75	625	313	156
100	833	417	208
167	1392	696	348
200	1667	833	417
250	2083	1042	521

Three-Phase Transformer Full Load Current (Ampere)

kVA Rating	240 V (A)	480 V (A)
3	7.2	3.6
6	14.4	7.2
9	21.7	10.8
15	36.1	18
22	53	26.5
30	72.2	36.1
45	108	54.1
75	180	90.2
112.5	271	135
150	361	180
225	541	271
300	722	361
500	1203	601
750	1806	903