## Determining motor slip

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### Determining motor slip

Q: I have an application which involves using one of your three-phase induction motors and a third party inverter (VFD). I am trying to calculate the frequency needed to run the motor at the speed that I require. I found this equation and I need help determining the slip of your motor:

Motor slip - induction motor RPM formula, frequency, poles, slip.jpg (62.46 KiB) Viewed 3619 times

A: As stated in the paragraph shown above, the slip will change based on the rotation speed of the motor.

Synchronous speed without slip:
Ns = 120 * F / P

where
Ns = synchronous speed in RPM
F = frequency in Hz
P = # of poles

Synchronous speed with slip:
Ns = 120 * F * (1*S) / P

S = Ns - N / Ns

where
N = speed under a given load in RPM

Because speed makes a difference in motor slip, we do not provide a value for slip for our AC induction motors. Instead, we provide the following specification for our older induction motors (FPW and WK2 series motors):

"The speed is calculated by dividing the motor's synchronous speed (50 Hz: 1500 RPM, 60 Hz: 1800 RPM) by the gear ratio. The actual speed is 2~20% less than displayed value, depending on the load."

This means that for each application, the actual speed of the motor may vary due to the load that is being rotated. The only way to calculate the required frequency for your specific application is to test a frequency value and fine tune that value to produce the output speed that you require from the motor.
For a smaller speed variation (or value of slip), consider going with our newest KII series three-phase induction motors. The KII series three-phase induction motors have the following specification:

"The speed is calculated by dividing the motor's synchronous speed (50 Hz: 1500 RPM, 60 Hz: 1800 RPM) by the gear ratio. The actual speed is 2~10% less, depending on load".

Please click below to view features and specifications of the KII series:
http://www.orientalmotor.com/products/a ... otors.html

JS

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