In applications where the driven machine presents a high starting load and/or there is a need to start with minimal current draw, a wound rotor (or slip ring) motor can provide better starting performance. NHP Electrical Engineering Products offer a range of 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 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. While one of the methods for starting wound rotor motors is the multi-stage secondary resistance starter, it is understood that 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.
With many systems comprising 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 starters makes them a suitable proposition for any downtime critical plant and/or for remote installations where the availability of 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.
The fixed and moving electrode liquid resistance starters are suitable for use with heavy industrial machines such as Ball and SAG mills, crushers, conveyors, compressors, chippers, fans, pumps, mixers and saws.
The fixed and moving electrode liquid resistance starters have the following benefits:
- Easy to understand technology
- Optimum control over starting current, torque and motor/load acceleration
- No need for specialist electrical personnel or equipment
- Easy to maintain
- Suitable for downtime critical plant