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Motor Short Circuit Current Calculator

Free calculator estimate 3 phase AC motor short circuit current.

Motor Rating
Voltage
Power factor
%

Motor Rating Current
Motor Fault Current

3 Phase Short Circuit Current Calculation

A short circuit calculation for motor will provide the magnitude of fault current which will flow if a bolted short-circuit occurs at motor terminal. If the values of prospective fault currents are known, it is possible to select protection devices (viz. circuit breakers, fuses), associated cables, motor control centers, and switchgear capable of withstanding the fault. It also is necessary to know the potential fault current values at in order to properly set protective relays for coordinated protection during a fault.

There are several ways of preparing short circuit calculations including:

  • MVA method
  • IEEE per-unit method
  • Ohm method

The MVA method is probably the easiest to perform manually. The ohm method is mainly used by software used since it ask extensive calculations to reflect impedances .

How to Calculate Short Circuit Current of Induction Motor

In rotating machine, impedance will vary during fault period from sub-transient, transient to steady state. To simplify calculations, a sub-transient impedance will be used to come up with an extreme result from motor contribution.

Following induction motor values is applied to obtain a motor short circuit current contribution in calculator for multi-voltage industrial systems:

  • Motors each less than 50 hp, using impedance of 0.28 based on motor rating.
  • Motors 50 hp and larger, using impedance of 0.2 based on motor rating