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kW & HP
HP = kW x 1.340
1kW = 1.340 HP
1HP = 746Watt

 

Single Phase
1kVA = 1kW (Power Factor = 1)
kVA = Watt ÷ Amps
Watt = Volt x Amps
Volts = Watt ÷ Amps
Three Phase
kVA = Amps per Phase ÷ 1.52
Power Factor = 0.8 (kW = kVA x 0.8)
kVA = kW ÷ 0.8
   
To Calculate the Amps an Alternator can Produce (provided it is fitted to adequately powered engine)
Single Phase
Amps an alternator can produce
Amps = kVA x 1 000 ÷ 230
Example:
Amps = 12 x 1 000 ÷ 230 = 52A
Three Phase
Amps/Phase an alternator can produce
Amps/Phase = kVA x 1 000 ÷ 400 ÷ 1.732
Example:
Amps/Phase = 20 x 1 000 ÷ 400 ÷ 1.732 = 28.9A/Phase
   
To calculate kVA required when Current (Amps) is known
Single Phase
kVA Required = Amps x 230 ÷ 1 000
Example:
kVA Required = 52A x 230 ÷ 1 000 = 11.96kVA
Three Phase
kVA Required = Amps per Phase ÷ 1 000 x 1.732 x 400
Example:
kVA Required = 28.9A ÷ 1 000 x 1.732 x 400 = 20kVA

 

To determine the kVA the engine can produce AT SEA LEVEL (Note that the same calculations are used for 3 000rpm & 1 500rpm)

Single Phase
kWm x 0.Eff of Alternator = kVA (Divide answer by 0.82 for altitude conditions)
Ex: 7kW x 0.79 = 5.53 kVA at sea level

Three Phase
kWm x 0.Eff of Alternator ÷ 0.8 (PF) = kVA (Divide answer by 0.82 for altitude conditions)
Ex: 10kW x 0.83 ÷ 0.8 (PF) = 10.375 kVA at sea level

 

Engine Selection

kVA x Power Factor ÷ Alternator Eff ÷ 0.746 = HP required at 3 000rpm (or 1 500rpm)
(Power Factor for Three Phase = 0.8 and 1 for Single Phase)
Example:
6kVA x 1 ÷ 0.79 ÷ 0.746 = 10.18 HP on shaft at sea level (Divide answer by 0.82 for altitude conditions)

 

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