Three Phase Power Equations

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Some common three phase power equations can be expressed as

Real Power

W_applied = 3^1/2 U I cos Φ

             = 3^1/2 U I PF        (1)

where

W_applied = real power (W)

U = voltage (V, Volts)

I = current (A, Amps)

PF = cos Φ = power factor (0.7 - 0.95) 

For purely resistive load: PF = cos Φ = 1 

• resistive loads converts current into other forms of energy, such as heat
• inductive loads use magnetic fields like motors, solenoids, and relays

Example - Pure Resistive Load

For purely resitive load and power factor = 1, the real power in a 415 Voltage 20 Amps circuit can be calculated as

  W_applied = 3^1/2 415 (V) 20 (A) 1

         = 14400 W

         = 14.4 kW

Total Power

W = 3^1/2 U I         (2)

Brake Horsepower

W_BHP = 3^1/2 U I PF μ / 746         (3)

where

W_BHP = brake horse power (hp)

μ = device efficiency

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Related Topics

• Electrical - Amps and electrical wiring, AWG - wire gauge, electrical formulas, motors and units

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