AC Theory, Power Factor, and Circuit Design

Impedance in an AC circuit is voltage divided by current (Z = V / I).

Apparent power (kVA), real power (kW), and reactive power (kVAR) form the power triangle.

Power factor equals real power divided by apparent power (kW / kVA).

In a wye system, line current equals phase current and line voltage is 1.732 times phase voltage.

In a delta system, line voltage equals phase voltage and line current is 1.732 times phase current.

Three-phase power = 1.732 x V x I x power factor.

A 208Y/120-V system has 120 V line-to-neutral; a 480Y/277-V system has 277 V line-to-neutral.

Capacitor kVAR for correction = kW x (tan(theta1) - tan(theta2)).

Triplen (3rd-order) harmonics add in the neutral of a three-phase, four-wire system.

Neutrals of predominantly nonlinear loads are counted as current-carrying conductors for adjustment.

Continuous loads are sized at 125% of the load current for conductors and overcurrent devices.

Demand factor is maximum demand divided by connected load and is always 1 or less.

Balancing phase loads reduces neutral current and improves system efficiency.

Single-line diagrams use one line and standard symbols to represent the power system.