Sizing a Generator

Method 1
Method 2
Single Phase
Three Phase
Single Phase
Three Phase
  • Measure the total current flowing with all equipment switched on that need to be supplied.
  • Multiply the current with the supply voltage and divide by 1000 to get a kVA figure . Multiply kVA with 0.8 to get a kW figure.
  • This kVA and kW figures are continuous generator power and not standby. Standby figures will be higher.
  • Measure the current flowing through all three phases with all equipment switched on that need to be supplied.
  • Add the three current values (a safer practice is to multiply the highest reading by 3).
  • Multiply the current with the supply voltage and divide by 1000 to get a kVA figure.
  • Multiply kVA with 0.8 to get a kW figure.
  • Add the Watt values of all equipment together. Equipment starting values should be used.
  • Divide by 1000 to get a kW value.
  • Divide the kW value by 0.8 for a kVA value.
  • This kVA and kW figures are continuous generator power and not standby.
  • Add the Watt values of all equipment together. Equipment starting values should be used.
  • Divide by 1000 to get a kW value.
  • Divide the kW value by 0.8 for a kVA value.
  • This kVA and kW figures are continuous generator power and not standby.

Notes

1. In AC work the product of the supplied voltage and current drawn is VA, voltampere. This term is used to distinguish this quantity from power (Watt). Power in Watts = voltamperes x power factor. Power factor for a generator is normally 0,8.

2. When the current readings for the 3 phases in the method above differs significantly, you should get a qualified electrician to balance the 3 phases.