Affordable motor protection

November 2001 Motion Control & Drives

The locally designed and manufactured N Series motor protection relays, from NewElec, range from the NC relay offering basic protection to the more sophisticated NJ model. All types provide simple operation and reliability. The four models cover the current ranges 5 to 55 A, 20 to 220 A, 50 to 550 A and 10-110% of selected CT ratio, to accurately protect LV three-phase induction motors against overloads, phase unbalance, earth leakage and jam protection.

LED indication is provided for ease of operation. During a thermal lockout fault condition, a red LED indicates that the overload protection circuit has operated and that the thermal capacity available is less than 60% of the set value. This LED switches off once 60% capacity is available.

The earth leakage circuit operates on a core balance principle with a 250 mA sensitivity and a 100 ms trip delay. The main trip contacts of the NH and NJ relays are actuated provided the motor current is below 8 x Ifl. This feature prevents the motor contactor or any other device with insufficient rupturing capacity from attempting to clear a high-energy fault.

Both the NJ and NK relays provide a motor running jam protection feature which protects the driven plant against impact torques developed when jamming occurs during normal running conditions. A 100 ms trip delay is initiated when the motor load current exceeds 3 x Ifl. The NK and NJ relays' interface facility allows their potential free relay outputs to duplicate the red LED fault indicators to communicate with a PLC or telemetry interface.

NewElec

(012) 327 1729

newelec@pixie.co.za

www.newelec.co.za

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