Avoid problems wiring those motor drives!Variable Speed Drives (VSD) are an integral part of industry these days. The ability to electronically control the operation of motors has allowed for complex control systems to be realised at an affordable cost. However, there are some wiring rules that need to be followed in order to make the control system reliable and also to be a "good citizen" amongst other nearby control systems.
VSDs basically rectify the incoming mains AC voltage into DC and then, using high frequency switching, synthesize an output voltage whose amplitude and frequency is programmable and controllable. The use of high frequency switching produces an amazing amount of electro magnetic interference and high frequency currents, which if not handled correctly can disrupt the control system or other control systems nearby.
Some basic rules for wiring up VSDs are:
- Use good quality shielded cable from the VSD output to the motor
- Keep the output cable as short as possible. if long cable runs are unavoidable, use a VSD manufactuer recommended output filter and place this as close the the VSD as possible. Use shielded cable to connect it up!
- Earth the shield of the output cable at both ends (motor and VSD). This is not a substitute for the normal earthing of the motor. Make sure the motor is also earthed in accordance with local regulations as well.
- Keep all low voltage control wiring as far away as possible from the shielded cable and the VSD mains input wiring
- Keep all VSD mains wiring away from the mains wiring of other control systems
- "Star point" the earths in the control system. Do not share the VSD earth with any other system components