How to Calculate 3 Phase Transformer For 1 Phase Load?

If the single phase 1,000 kW load is a single load, then what Rakesh mentioned is correct.

But if the 1,000 kW load comprises of several individual single phase loads, then distribute the loads to 3 different groups, as equally as possible. Then multiply the largest group load by 3 and the result (converted to kVA using average power factor) should be the transformer capacity.

For example, if the individual loads are:

Load 1 – 100 kW

Load 2 – 150 kW

Load 3 – 200 kW

Load 4 – 250 kW

Load 5 – 300 kW

Load groupings:

Group 1: Load 1 + Load 4 = 350 kW

Group 2: Load 2 + Load 3 = 350 kW

Group 3: Load 5 = 300 kW

The maximum group load is 350 kW

The 3 phase transformer capacity requires to supply 350 x 3 = 1,050 kW

Assuming average power factor of the loads is 0.8, the transformer capacity is 1,050/0.8 = 1,312 kVA. Considering some reserve loads, you can select a 3 phase transformer of size 1,500 KVA or more.

Each group of loads shall be connected to each phase of the transformer.

- MS