Aiming to increase the efficiency of energy-consuming products, the Energy-related Products Directive has made it necessary for motor manufacturers to make changes to their designs. Manufacturers now use thicker wires for windings to reduce resistance, optimised laminations to reduce losses from stray magnetic fields and higher quality steel to reduce hysteresis losses. As a result, high efficiency motors now have increased inductance, leading to larger starting currents. Therefore, contactors and motor-protection circuit breakers must be able to cope reliably with these developments.
To suit IE3 motors, Eaton has upgraded the characteristics of its PKZ and PKE motor protection circuit breakers as the starting current provision of 8x normal full load current is not sufficient. To prevent conditions such as contactor ‘bounce’, the devices now allow for starting currents as high as 12x to 15.5x full-load current.