Frequency converter operation

The motor in series design (confirming to IEC 60034‑17) can be operated with a frequency converter. Contact customer service if the rated voltage is above 415 V/50 Hz or 480 V/60 Hz. Because of the additional heating caused by harmonics, the rated power of the motor should be around 10 % more than the power requirement of the mixer. For frequency converters with a low-harmonic output, it is possible to reduce the 10 % power reserve. Harmonic waves are reduced by means of output filters. Synchronise the frequency converter and the filter with each other!

The configuration of the frequency converter depends on the rated motor current. Make sure that the mixer operates across the entire control range without jerking or vibrating (without vibrations, resonance, oscillation). Otherwise, the mechanical seals may leak or be damaged. Increased motor noise caused by the harmonics of the power supply is normal.

During parameterisation of the frequency converter, observe the setting of the quadratic characteristic curve (U/f characteristic curve) for submersible motors! The U/f characteristic curve ensures that the output voltage at frequencies less than the rated frequency (50 Hz or 60 Hz) is adjusted to the power requirement of the mixer. More recent frequency converters feature an automatic power optimisation function - this automation achieves the same effect. For the frequency converter setting, refer to its installation and operating instructions.

Motor monitoring faults may occur if the motor is operated with a frequency converter. The following measures can reduce or avoid these faults:

  • Keeping within the limit values stated in IEC 60034‑25 for overvoltage and rise speed. If necessary, install output filters.
  • Vary the pulse frequency of the frequency converter.
  • In the event of a fault in the internal sealing chamber monitoring, use the external double-rod electrode.

The following construction measures can help to reduce or prevent faults:

  • Separate connection cables for the main and control cable (depending on the motor size).
  • Keep an adequate distance between main and control cable during routing.
  • Use shielded connection cables.

Summary

  • Min./max. frequency during continuous duty:
    • Asynchronous motors: 30 Hz up to rated frequency (50 Hz or 60 Hz)
    • Permanent magnet motors: 30 Hz up to the stated maximum frequency as per rating plate
    • NOTICE! Higher frequencies are possible following consultation with customer service!
  • Observe additional measures with regard to EMC regulations (choice of frequency converter, using filters, etc.).
  • Do not exceed the rated current or rated speed of the motor.
  • Connection for bimetallic strip or PTC sensor.