When using a VFD (Variable Frequency Drive) to run an electric motor, why can long cable distances between the drive and the motor cause problems or even damage the motor over time? How do these long cables affect voltage spikes, insulation stress, heating, and overall motor life?
When a VFD is connected to a motor with a long cable, the fast voltage pulses from the VFD bounce back in the cable. These reflections create high voltage spikes, sometimes going up to 1300–1600 volts on a 400-V motor. These spikes hit the motor windings and can damage the insulation over time.
To prevent this, we use dv/dt filters or sine filters to smooth the pulses.
Standards like IEC 60034-17 also tell us how long the cable can be for safe operation. This simple idea helps maintenance teams understand why motors fail and how to avoid future problems.