Variable frequency drive for motors

The VFD motor shall be speed controlled corresponding to 4-20 mA or 0-10V reference input signal, the VFD shall automatically run at constant speed as at 80-110% of the last speed reference available prior to the loss of signal. The power controller shall be controlled to always start the motor in the forward direction. Logic shall be provided to prevent the motor from being started in the reverse direction.

A high resistance ground system would add typically 150-200 'sto the Fig. 8 T1 secondary neutral circuit that is grounded. This resistor is in the series path of the CM noise current return and significantly reduces peak CM current magnitude to small levels such that potential differences in the plant ground grid caused by CM noise is minimal. Surge testing has shown acceptable primary to secondary line to ground transient voltage reduction.

Once it's determined that the application falls within the required specific conditions, the next step is detailed design, where care must be taken to select and apply the right variable frequency drive and associated components.