In applications where the driven machine presents a high starting load and/or there is a need to start with absolute minimal current draw, a wound rotor (or slip ring) motor can provide unparalleled starting performance. NHP offers a range of Australian made and industry proven fixed and moving electrode liquid resistance starters for use with low and medium voltage wound rotor motors from 200 kW to 12.4 MW.

The issues

The torque and current versus speed characteristics of a wound rotor motor can be altered and controlled through the addition of resistances to the rotor circuit. Whilst one of the more common methods for starting wound rotor motors is the multistage secondary resistance starter, it is understood the resistors can generate substantial amounts of heat during starting, provide inconsistent starting performance and require frequent and costly maintenance.

Close control of starting torque and current also requires more resistance stages adding complexity and cost to the motor control system.

The Solution

With many systems comprising little more than a tank which holds an electrolytic solution, thermostats and floats to monitor electrolyte temperature and level, and an enclosure which houses a shorting contactor and timer, the simplicity of liquid resistance makes them the ideal proposition for any down time critical plant and/or for remote installations where the availability of specialist electrical personnel may be limited. For these reasons electrical engineers and equipment specifiers’ have turned their attention to liquid resistance starting of wound rotor motors.

Key Benefits

- Simple, easy to understand technology
- Optimum control over starting current, torque & motor/load acceleration.
- High reliability
- No need for specialist electrical personnel or equipment
- Easy to maintain
- Ideal for down time critical plant