Waldiberto de Lima Pires, WEG Electric Motors Corporation
Since the motor losses constitute heat sources, the loss reduction obtained by using this method for driving the motor results in significantly better thermal performance than the same motor operating under constant flux conditions (Figure 3). These theoretical results have also been confirmed experimentally on a wide range of NEMA high efficiency, NEMA premium efficiency and EFF1 motors ranging from 5-hp to 300-hp.
Figure 3. Temperature rise vs. operational frequency showing motor performance under constant flux and optimal control strategies
The Benefits of OptimalFlux Control
The combination of a standard off-the-shelf NEMA High or Premium Efficiency induction motor and a standard variable frequency drive with these optimal capabilities delivers several benefits to the pump user. First and foremost, TEFC NPE motors driven using these techniques run significantly cooler than inverter class solutions using traditional constant flux drive strategies, so they last much longer on the factory floor. Typically, for each 10-degC of operating temperature reduction, motor life doubles. Motors powered by these new methods will operate cooler over their entire speed range than when driven using the traditional constant flux technique.
Longer motor life leads to reduced motor maintenance costs and less downtime. Since this optimal run solution can be based used in other applications like compressors and conveyor belts throughout the plant, lower spares inventory and related costs can be achieved.