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- Jun 12, 2014
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Agreed. It is probably more precautionary, and this subject has been discussed extensively in a previous thread(s). I believe there are varied suggestions based on incomplete information on the motor specifics, type, age, wiring configuration, etc. There are probably different recommended connection configurations depending on the motor and VFD combination. If you had a standard single speed 3 phase inverter rated motor, a 4 pole motor, it should be capable of running at 120Hz without problems. Each manufacturer has there own recommendations, but I did call several of them a while back and the usual was 2X the base speed for a 4 pole. But performance characteristics may deteriorate in a non-linear fashion above ~90-100Hz unless the motor specs specifically states otherwise (usually vector motors). Most of my 3 phase inverter/vector motors run and are rated to 120Hz. You're motor most likely does not fall into this category, so something like 90Hz might be the maximum, and that assumes you need that speed. If you are running constant torque, then you would most likely use the higher RPM speed wiring and the VFD would provide constant torque below the base speed.
The major concern as previously outlined is matching the motor characteristics to the low or high speed connection configuration of the motor. I have no experience in this area, so will differ to others as to what might be best for you, or you can experiment and see what gives the best performance. In theory the more elaborate VFDs have configuration for 2 motors, one could program a set of variables for the low and high speed connections.
