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Motor protection relays help OEMs to cut costs

26 May, 2015

The Brazilian motors and controls manufacturer WEG used the recent Hannover Fair to launch a series of electronic motor protection relays with a wide current adjustment range of 1:5, allowing OEM machine-builders to stock fewer spares and to save time that would be needed when designing machinery to accommodate different relays with narrower specifications. The RW_E relays are also claimed to dissipate 87% less power than conventional thermal devices, thus saving energy.

“In an increasingly globalised and competitive market, it is common for machine manufacturers to provide their customers with a wide choice of electric motors with a huge number of different models and output powers,” points out Marek Lukaszczyk, WEG’s European & Middle East marketing manager. The new relays, he says, “mean that machine manufacturers can now standardise their control panels, saving time.”

The relays come in ratings from 0.4–840A and protect motors rated up to 690V AC against overheating due to overloads, phase drop-outs or phase asymmetries. They are powered by the motor’s current, thus avoiding the need for external power connections. A thermal memory models the heat balance in a motor to optimise the protection.

The relays’ low power dissipation helps to reduce heat loads in switching cabinets and allows equipment in switchgear sets approved to IEC 61439 to be replaced without needing new certification.

WEG's electronic motor protection relays have a wide current adjustment range

The relays are said to be as easy to use as bimetallic motor protection relays, and offer manual or automatic reset after tripping. Trip classes 10, 20 and 30 for normal and heavy-load starting can be set from the front panel. Temperature compensation ensures high trip accuracies from –20°C to +60°C.

The relays are manufactured and tested to IEC/EN 60947 and UL 60947-4-1A. They can be combined with WEG's CWM and CWB contactors to produce compact motor starter sets.

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