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Mariner's Formulae Quick reference guide
Electrical Formulae
 
OHM'S LAW

Resistance, R =  Voltage  [ohm]
                         Current

Current, I =    Voltage    [ampere]
                   Resistance

Voltage, V = Current x Resistance [volt]


SINGLE PHASE A.C. POWER

Power = V x I x cosΦ [watt]

            where cosΦ = power factor


THREE PHASE A.C. POWER

Power = 1.732 x V x I x cosΦ [watt]


SERIES A.C. CIRCUIT

Reactive or 'Idle' Component = tanΦ x kW  [kVAR]

Reactive kVA =  kVAR  = (kW2 + kVAR2)½  [kVA]
                        sinΦ

Active Component = kVA x cosΦ  [kW]


EFFICIENCY

Efficiency =  746 x Output Horsepower 
                            Input Watts


INDUCTION MOTOR

Synchronous Speed, Ns =  120 x frequency (hertz)    [rpm]
                                             number of poles

Actual Speed, N = Ns(1-slip)  [rpm]

Rotor output = Torque x 2 x π x N  [watt]

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