Engineering Formulas
Quantity Symbol Unit Symbol Example
apparent power S Voltage x Current VA 120kVA (1000 x V x I )
current I Ampere A
efficiency η per unit 0.95 (i.e. 95%)
frequency f Hertz Hz 50 Hz
poles p number 2 pole, 4 pole
pole pairs pp number 4 pole is 2 pp
active power P Watt W kW = 1000 x W
power, input Pin Watt W
power, output Pout Watt W
power factor pf per unit 0.86
reactive power Q Voltage x Current reactive var
slip s per unit
speed N revs per minute Not SI unit
torque T Newton . metre Nm
voltage V Volt V

Quantity DC AC 1 Phase AC 3 Phase
Current (I)
Efficiency
Power Factor

Formula

Quantity Formula
Fan load power
Fan load power
Ohm’s Law

(Resistive circuits)

Power (kW)
Power (Hp)
Power Factor
Pump load power (Hp)
Pump load power (kW)
Slip, s,  (p.u.)
Slip,  (%)
Synchronous speed, NS,  (rpm)
Torque (N.m)
Torque (lb.ft)

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