Eliminating impact torque conditions
4th Quarter 2015
Shaft power components
The OLR 84 S protection relay from NewElec, when mounted on a motor circuit, eliminates impact torque conditions which can result in broken chains, damaged screw conveyors, broken couplings and even damaged gearboxes.
The OLR 84 S relay has two settings. The first designates the total start time for the given motor in seconds through a range up to 50 s while the second designates the load trip threshold. The latter setting is percentage calibrated from 30 to 120% of the selected CT ratio XXX:1. It is necessary for the user to select an appropriate ring CT that will cover the expected trip threshold current. A general rule is that if the motor load maximum current is x A, the user must select a current transformer where 3x A is about mid-scale. The reason for this is that a stall or jam condition usually manifests itself at about three times motor full load when the motor develops an output torque in the region of 2,5 to 3 times its normal rated torque. This output torque will then be amplified through a factor dependent on the gearbox ratio.
The OLR 84 S permits the starting current for the motor start but will cause a trip in 100 ms if the motor load suddenly exceeds the upper trip threshold where the motor enters a stall condition after the starting sequence. In doing so, it will interrupt the supply to the motor by means of the main holding contactor and prevent mechanical fractures in the production process.
For more information contact NewElec, 086 010 3041, [email protected], www.newelec.co.za
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