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SSOLR on drive output.

Issue:
 SSOLR on drive output. Could you please provided details/ white papers for use of SSOLRs with VFDs?
 
 
Product Line:
 Solid State OverLoad Relays
 
 
Environment:
 Solid State Overload Relays used on Variable Frequency Drives
 
 
Cause:
 Nuisance tripping
 
 
Resolution:

There are no white papers for using any SSOLR on the output of a drive. This is not a recommended application.

Typically the drive will be monitoring the current that it is providing to the motor and will signal an overload condition. Thus the use of an overload on the drive output is redundant.

Understanding that there may be a need to use a bypass contactor to run the motor should the drive require servicing, the recommendation then is to place the overload ahead of the bypass contactor. With this placement, the SSOLR will not see the output of the drive but will still provide overload protection for the motor when the drive is bypassed.

All of our SSOLR devices are CT driven. The output of a CT will fall off at low frequencies that may be produced by the drive so the SSOLR would not be providing proper protection. Further, many, if not most, drives will produce an output with high harmonic content. The CT will pass the harmonics on to the electronics and can cause the nuisance tripping that you reference.
 

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