Electrical Power
Motor power calculations
Single-Phase Power
Real Power (P)
—
Three-Phase Power
Real Power (P)
—
Electrical Power Formulas
Single-Phase AC Power
P = V × I × cos(φ)
P = Real power (W)
V = Voltage (V)
I = Current (A)
cos(φ) = Power factor (0-1)
V = Voltage (V)
I = Current (A)
cos(φ) = Power factor (0-1)
Three-Phase AC Power
P = √3 × V × I × cos(φ)
√3 = 1.732 (constant for three-phase)
V = Line-to-line voltage (V)
I = Current per phase (A)
Alternately: P = 3 × V_phase × I × cos(φ)
V = Line-to-line voltage (V)
I = Current per phase (A)
Alternately: P = 3 × V_phase × I × cos(φ)
Reactive & Apparent Power
Q = V × I × sin(φ)
S = V × I
Q = Reactive power (VAR)
S = Apparent power (VA)
Power triangle: S² = P² + Q²
S = Apparent power (VA)
Power triangle: S² = P² + Q²
Typical Power Factors
0.95-1.0: Pure resistive load, efficient
0.85-0.95: Typical motor running
0.70-0.85: Motor starting, induction motor
0.50-0.70: Poor; requires correction
0.85-0.95: Typical motor running
0.70-0.85: Motor starting, induction motor
0.50-0.70: Poor; requires correction
Motor Efficiency & Power
P_shaft = P_input × Efficiency
Typical motor efficiency: 85-95%
P_input = Electrical power drawn (kW)
P_shaft = Mechanical power output (kW)
P_input = Electrical power drawn (kW)
P_shaft = Mechanical power output (kW)