Single Phase Power Equations

Single phase power equations:

Real Power

W_applied = U I PF / 1000                             (1)

where

W_applied = real power (kilowatts, kW)

U = voltage (volts, V)

I = current (amps, A)

PF = power factor - 0.7 - 1

Total Power

W = U I / 1000                                     (2)

Brake Horsepower

• Brake horsepower is the actual power delivered to or by a shaft.

W_BHP = U I PF μ / 746                          (3)

where

W_BHP = brake horsepower (hp)

μ = device efficiency

Example - Horsepower vs. Current and Voltage

An AC motor consumes 8 amps of current. The voltage supplied is 12 V, the efficiency of the system is 96% (0.96) and the power factor is 1. The horsepower can then be calculated as 

W_BHP = (12 V) (8 A) (1) (0.97) / 746  

         = 0.125 HP

         ≈ 1/8 HP