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Single Phase Power Equations

Power equations for single phased electrical systems.

Single phase power equations:

Real Power

Wapplied = U I PF / 1000                             (1)

where

Wapplied = 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.

WBHP = U I PF μ / 746                          (3)

where

WBHP = 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 

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

         = 0.125 HP

         ≈ 1/8 HP 

 

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