Single Phase Load Estimate to Three Phase Power Supply

[Locus]

Hi Everyone

I would be glad if you could clarify this for me:

For a Load Estimate Survey whereby 95% is single phase, the Load Estimate is 90 KVA (Single Phase). However, the power supply is three phase 4 wire system.

To calculate the current per phase, the 90 kVA is divided by three i.e. 30 kVA per phase. Hence, current per phase is (30 x 1000/230) = 130 A/ph.

Hence, the 90 kVA single phase is equal to 90 kVA three phase??? This is where I'm confused.

In addition, to undertake a load estimate survey, which is better to workout all the currents or use the kW or kVA ratings with Utilisation factor & simultaneity factor.

Thanks in advance.

 

[telectrix]

a 90kVA 3 phase supply will give you approx 30kVA per phase assuming the loads are balanced across the 3 phases. it would be wise to allow 20 -25% additional capacity to allow for some imbalance.

 

[Locus]

No, its 90 kVA Single Phase Load Estimate. Hence, if the power supply is three phase. Then, if the load is properly balanced for the three phase, the load per phase will be 30 kVA. Am I right?

Hence, I'm confused that 90 kVA Single Phase Load is equal to 90 kVA Three Phase Load.

 

[David Prosser]

You are not the only one confused. I don't even understand what you are asking.

 

[Locus]

Sorry David, I'll try to explain more clearly.

The total estimated single phase loads for a building is approx. 90 kVA i.e. all the equipment are single phase (socket-outlets, pumps and lighting).

However, the building has a three phase power (4 wires) supply from the utility.

If the single phase loads (90 kVA) are distributed equally over the three phase power, then the apparent power per phase is 30 kVA & the total three phase power is 90 kVA. Is this right?