Reducing harmonics

Reducing harmonics Reducing harmonics

Changing the pulse rate or switching the drive inverter transistor to a slower frequency can eliminate the low-order harmonics of high electrical power. Also, filters, reactors and isolation transformers can be added to lop off harmonics and block spikes. Designers must keep in mind, however, that these add-ons do cause voltage drop between power supply and motor.

If these measures are taken, cable is left the weakest link in a VSD system. That is why since 1996 National Electrical Code Article 430-22a has specified that source-power cable conductors must be sized at 125% of the full load current of the drive. This requirement protects cables from power distortions generated by the rectifier and ensures safe and uninterrupted operation. This ensures that the cable will not fail due to power downtown distortions — so the whole system is able to handle the type of power that a VSD drive generates.