How to

How to do the VFD commissioning and testing?

Pre-commissioning procedure of VFD

  • Make sure the installation of the VFD is complete and proper
  • Check for damage in the VFD
  • If there is any damage, then the VFD must be repaired
  • The insulation of the incoming and the outgoing power wiring must be checked
  • We need to check if the incoming and outgoing wires are terminated to their respective equipment with proper polarity
  • Check if the VFD cable dressing is properly done
  • Make sure that the earthing is properly done
  • Check the fuses and other protective devices

Testing of insulation

  • Connection tightness must be checked
  • The incoming and the outgoing cables must be isolated
  • Megger testing
  • Verify the earth loop impedance

VFD commissioning procedure

Visual inspection

  • Check if the ratings of the VFD and the motor is compatible and this can be done by checking the specifications in the motor nameplate
  • The voltage and current in the nameplate must be checked for the contactors, fuses, and breakers
  • The overload devices must be compared with the full load motor current for proper sizing
  • We must check if the grounding is properly connected to the main grounding
  • Check the isolation transformers rating
  • Check if the overload devices and parameter settings of the VFD is properly done or not
  • Check if the voltage, the current transducer is installed properly and wired
  • Output inductors rating should be checked

Mechanical inspection

  • Check if the motor is properly mounted or not
  • The shaft of the motor shouldn’t have any restriction for rotation
  • The switching device, contactors, and isolating devices should work properly

Electrical tests

  • Power cable insulation resistance must be checked, the cables from the VFD to the motor.
  • PTC sensor cables should be properly terminated to the drive
  • Check the motor heater supply to the terminal and also check if the heater is working properly
  • Motor bearing heater supply and the bearing lubricant supply must be checked
  • Check the ratio of the current and voltage transformer
  • Check if the temperature sensors are properly working
  • Thermal overloads, operation, and calibration should be checked by current injection and also test the internal protection of the VFD

VFD and motor no load test

  • Check if the motor is uncoupled and isolated from accidental contacts
  • Make sure the pre-commissioning is done properly
  • Check all the circuits
  • Ensure the PTC sensor resistance is up to the drive relay point and also make sure the sensor is properly installed
  • Make sure the control cables are properly set for the start, stop, speed, current, and also check the feedback from the DCS is proper from the drive up to the DCS.
  • In order to do the visual inspection of the drive open all the panel doors and make sure that the VFD is clean of dirt
  • Check if there is any loose material in the drive panel
  • Make sure all the components are installed in the proper place
  • We must check certain connections such as the supply cable from the distribution board to the VFD and also the connection of the converter and inverter unit to the bus bar. Check the cables from the drive to the motor.

What are the factors that could affect the quality of VFD?

  • Poor power quality
  • High temperature
  • High altitude

So if the VFD is subjected to the above mentioned factors then it would exhibit certain symptoms such as erratic behavior, frequent faults, and the service life will be shortened.  

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