Operator Interfaces, Switches & Relays


Protection for wound rotor motors

January 2010 Operator Interfaces, Switches & Relays

NewElec‘s 330 series motor protection relays are specifically designed to meet the protection requirements of wound rotor motors used on winches and overhead cranes. The information necessary to obtain proper protection can easily be found on the manufacturers nameplates that are fixed to the motor. NewElec uses these technical ratings to formulate a thermal model, tailor made for the protected motor.

In order to correctly manufacture a suitable protection relay for these motors it is necessary to find the thermal rating of the machine, number of starts per hour and the cyclic duration factor (for example 25% CDF or 60% CDF).

Where crane operators are expected to operate their cranes within the motor ratings an additional ‘trip state indicator’ may be fitted inside the cabin. The benefit being that the operator has a visual display of the crane main hoist motor thermal utilisation and is able to ‘lean-off’ or extract more from the working of the crane dependent on the thermal capacity available.

The relays are remarkably accurate and will provide protection against overloading as well as phase unbalance. Users have a choice of door or chassis mounting and 110 or 220 VAC supply voltage.

For more information contact Luc Dutrieux, NewElec, +27 (0)12 327 1729, [email protected], www.newelec.co.za



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