Variable speed with power supply voltages ≥ 500 V
When motors are powered by frequency inverters with input voltages of 500V or more, several issues can affect their performance and lifespan.
High voltage increases stress on the winding insulation, which can lead to early failure. Inverter-driven systems produce voltage spikes and transients that worsen this effect, causing partial discharges that gradually damage the insulation.
When operating under these conditions, BITZER recommends to
- use shielded cables,
- shorten the cables as much as possible, if cable length ≥ 10 m, install a dV/dt filter at the inverter output (sinus filter is a possible option),
- limit dV/dt 1000 V at rise time ≥ 0.2 μs.
Using shielded cables can help to contain electromagnetic interference (EMI) and reduce the likelihood of induced voltages that can stress the motor windings.
Additionally, shorter cables reduce the inductance and capacitance in the system, thereby minimizing the amplitude of voltage peaks and transients.
dV/dt filters are designed to limit the rate of voltage change, thereby reducing the magnitude of voltage peaks. Such filters can therefore significantly enhance the reliability and lifespan of motor windings.
When using permanent magnet motors in sensor-less mode, the addition of dV/dt or sine wave filters may interfere with position estimation.
This should be carefully evaluated to avoid loss of synchronism. Always consult the drive manufacturer’s guidelines and adjust control parameters accordingly.
Further technical information can be found in the following standards:
- NEMA MG1 Part 30
- IEC 60034‑25