General Calculations 

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

Single Pase 

• 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 (Devide 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 (Devide 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
• (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 (Devide answer by 0.82 for altitude conditions)