Three-Phase Power Equations

Electrical 3-phase equations

Most AC power today is produced and distributed as three-phase power where three sinusoidal voltages are generated out of phase with each other. With single-phase AC power there is only one single sinusoidal voltage.

Some common three-phase power equations can be expressed as

Real Power

Wapplied = 31/2 U I cos Φ

             = 31/2 U I PF        (1)

where

Wapplied = real power (W, watts)

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 resistive load and power factor = 1, the real power in a 415 voltage 20 amps circuit can be calculated as

  Wapplied = 31/2 415 (V) 20 (A) 1

         = 14400 W

         = 14.4 kW

Total Power

W = 31/2 U I         (2)

Brake Horsepower

WBHP = 31/2 U I PF μ / 746         (3)

where

WBHP = brake horse power (hp)

μ = device efficiency

Related Topics

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

Related Documents

Tag Search

  • en: 3 three-phase electrical power voltage current

Search the Engineering ToolBox

- "Search is the most efficient way to navigate the Engineering ToolBox!"

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your SketchUp model with the Engineering ToolBox - SketchUp Extension/Plugin - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro. Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

Translate the Engineering ToolBox!
About the Engineering ToolBox!

close