Contents

Horsepower


Single Phase: HP = \frac{I\times V\times Eff \times PF}{746}

Three Phase: HP = \frac{I\times V\times 1.732\times Eff \times PF}{746}

Direct Current: HP = \frac{I\times V\times Eff}{746}

Current


Single Phase: I = \frac{746\times HP}{V\times Eff\times PF}

Three Phase: I = \frac{746\times HP}{1.732\times V\times Eff\times PF}

Direct Current: I = \frac{746\times HP}{V\times Eff}

Efficiency


Single Phase: Eff = \frac{746\times HP}{V\times I\times PF}

Three Phase: Eff = \frac{746\times HP}{1.732\times V\times I\times PF}

Direct Current: Eff = \frac{746\times HP}{V\times I}

Power Factor


Single Phase: PF = \frac{Input Watts}{V\times I}

Three Phase: PF = \frac{Input Watts}{1.732\times V\times I}

Direct Current: Not Applicable

Motor Output


Horsepower: HP = \frac{TRQ (lb.ft.)\times RPM}{5250}

Kilowatts: KW = \frac{TRQ (Nm)\times RPM}{9550}

Torque (lb. ft.): TRQ = \frac{HP\times 5250}{RPM}

Torque (Nm): TRQ = \frac{KW\times 9550}{RPM}

Speed - AC Machinery


Synchronous RPM: RPM = \frac{120\times HZ}{Number of Poles}

Percent Slip: SLIP = \frac{Synchronous RPM = Full Load RPM}{Synchronous RPM} \times100

Time for Motor to Reach Operating Speed (in Seconds)


  • Seconds = \frac{Wk^2 (lb.ft.^2) \times Speed Change (RPM)}{308\times Ave. Accelerating Torque (lb.ft.)}
  • WK^2 = Inertia of Rotor + \frac{Inertia of Load\times Load RPM^2}{Motor RPM^2}
  • Average Accelerating Torque = <tex>\frac{[(FLT + BDT)/2] + BDT + LRT}{3}

Shaft Stress


  • Shaft Stress (psi) = \frac{HP \times 321.000S}{RPM\times D^2}
  • Shaft Stress (kg/mm^2) = \frac{KW\times 4.96\times 10^6}{RPM\times D^2}
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