3-Phase Power Equations
In a balanced three-phase system, power can be calculated using the line-to-line voltage and line current.
Frequently Asked Questions
For a balanced 3-phase load, the Active Power (P) in Watts is calculated as: P = √3 × V_line × I_line × Power_Factor.
Three-phase power is a type of electrical power transmission using three alternating currents, each offset 120° in phase. It is the standard for industrial and commercial power distribution because it delivers more power with less conductor material than single-phase, and efficiently drives three-phase motors and large equipment.
In a star (Y) connection: Line voltage VL = √3 × Phase voltage Vph (approximately 1.732 × Vph). In a delta (Δ) connection: Line voltage VL = Phase voltage Vph. For a standard 400V system, the phase voltage is 400 / 1.732 = 231V — which is why phase-to-neutral voltage in Europe is 230V.
Apparent power S (kVA) = √3 × VL × IL / 1000. Where VL is line-to-line voltage in Volts, IL is line current in Amperes. To find line current: IL = S × 1000 / (√3 × VL). Apparent power is what the transformer and cables must handle, regardless of load power factor.
A balanced three-phase load has equal impedances on all three phases, resulting in equal currents and zero neutral current. An unbalanced load has unequal impedances, causing unequal currents and a neutral current. Unbalanced loads reduce efficiency, cause voltage distortion, and can damage sensitive equipment. VFDs and computers can cause significant imbalance.
Three-phase power transmits three times the power using only 1.73 times the conductor material of equivalent single-phase systems, making it ~73% more material-efficient. Three-phase motors are also self-starting, more efficient, produce smooth torque without pulsation, and have better power density than single-phase motors of the same output.