# Three-Phase Power Equations

## Electrical 3-phase equations

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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

W_{applied}= 3^{1/2}U I cos Φ

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

where

W_{applied}= 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

* 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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