Distribution Transformer Current Rating Calculator

Transformer current capacity calculator

If we have the kVA rating of the transformer available then the maximum full load current carrying capacity of transformer on the LT( 415 V side) and HT(11 KV side) side can be calculated through this transformer full load current calculator. enter primary side voltage 11 kV and secondory side voltage 415 V

What is a Distribution Transformer

The transformer which is used to distribute electricity in the household and small industries of consumers is called a distribution transformer. The rating of the distribution transformer is in kVA. The rating of the distribution transformer ranges from 10 KVA to 3 MVA. The main purpose of the distribution transformer is to supply electricity to the tail end users of the distribution network. The current carrying capacity of the distribution transformer is different on the low voltage and high voltage sides.

Need of neutral in distribution transformer

In distribution transformer, the primary side winding is always used to make in delta and the secondary side winding is used to made in star. The main reason for this is the need for neutral on the secondary side. As we know single-phase supply on the consumer side requires a phase to neutral 230 volts. Hence the secondary side is always low voltage and star type to meet the requirement of neutral. the neutral wire has always kept the grounded to make its voltage zero.

Rating of distribution transformer-

For getting the full load current capacity of a transformer, first of all, we need to know the type of distribution transformer on the basis of their rating-

Low power distribution transformer- 10 kva, 25 kva, 63 kva, 100 kva

Medium power distribution transformer- 250 kva 630 kva, 1 mva

High rating transformer- 2.5 mva, 5 mva,

Rating of a Three Phase Transformer:

 Three-phase transformer rating (kva) used to be calculated using the following formula-

 P = √3. V x I

Rating of a Three-phase transformer in kVA unit

KVA = (√3. V x I) /1000,

How to calculate transformer load capacity

Maximum Current carrying capacity can be calculated using its kva rating and voltage side –

For 100 kva, 3 phase transformer primary and secondary current calculation or current capacity of the distribution transformer on the LT(415 v) side can be calculated as follow-

100 kva transformer load capacity

 100 kva=√3.x 415v x I

 I= 100×1000 / 1.732 X 415v= 139 amp

similarly current capacity on h t side(11 kv side) shall be-

 I= 100×1000 / 1.732 X 11000 v= 5.25 amp

for 400 kva maximum current carrying capacity-

400 kva= √3.x 415v x I

I= 400 x 1000/√3.x 415v = 556 Amp

Sort cut / full load current formula for getting current capacity on LT side is also calculated using the following formula

Current capacity or full load current formula = kva rating * 1.39

100 kva transformer current rating will be= 100*1.39= 139 Amp

250 kva transformer current rating transformer will be= 250* 1.39 = 348 Amp

400 kva transformer current rating transformer will be =400*1.39 = 556 Amp

630 kva transformer will be= 630* 1.39= 875.7 Amp 

Transformer full load current chart

Rating of transformer Primary side full load current (amp)Secondary side full load current(amp)
  Line to line voltage= 11 kv Line to line voltage= 415 v
16 KVA 0.8422.3
25 KVA 1.3134.8
63 KVA 3.3187.6
100 KVA 5.25139
160 KVA 8.4222
200 KVA 10.5278
250 KVA 13.12347
400 KVA 21556
630 KVA 33876
1 MVA 52.491391
2 MVA 104.982782
2.5 MVA 1313478


This formula or calculator is only for countries where the LT voltage is 415v and the voltage on the ht side is 11kv. And the maximum load capacity of the transformer can be calculated through this formula. In the distribution network, the electricity department is required to do load balancing of the distribution transformer. And knowing how much the load is moving in the lt side, the load balance of the transformer can be done to keep the load running at less than the capacity of the transformer. That is, only after knowing the maximum load, we can save the load transformer from burning due to overloading.


Distribution Transformer: Construction | Type | Rating

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