This monthly column, submitted by SAPMA (SA Pump Manufacturers Association) guides and advises readers on the in's and outs of the pump world. Practical considerations for the use of AC variable speed drives & motors VSD compatible motor selection Not all standard AC motors are truly suitable for VSD applications. There are two main issues to consider: 1. Motor heat rise - a motor on a VSD will run at higher temperature than a D.O.L. motor. It is important for this additional heat rise to be minimal and to be precisely known. 2. Motor insulation - VSD output pulses have peak values (Vpeak) and sharp rise times (dv/dt) far above the normal grid 50Hz sine wave. These values as produced by the VSD and the corresponding motor insulation must be known and must be compatible.
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