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Don’t forget the installation basics

01 April, 2018

Poor installation is often to blame for VSDs failing in service. Andy Preston, ABB’s drives product manager in the UK, runs through some of the common reasons for VSD failures – and offers suggestions for avoiding such failures.

Most variable-speed drive (VSD) failures can be attributed to poor installation practices. Some failures can be avoided by using drives with built-in features to minimise mistakes and errors. For example, many of today’s keypads guide users through commissioning, making sure that nothing is forgotten and that the installation goes smoothly.

The most common reasons that VSDs fail include:

  • Location/environment  Many VSDs fail because they are used in environments that are too hot, too dusty, too damp or suffer from too much vibration. Most of these failures can be attributed to heat, either because of poor siting or ventilation, or because they are positioned in direct sunlight. Always check that a drive is designed for the environment in which it will be used.
  • Cable type  Selecting the correct motor cable is more critical than the supply cable. Fully shielded (screened), three-core symmetrical cables with separate equipotential earth bonds are recommended. The cable should not have a break in the shielding, even when it goes via an isolator box. Isolators need to be in metal enclosures to keep a continuous screen. Connections at the motor and drive ends need to be via metal glanding. Always check the manufacturer’s documentation.
  • Grounding (earthing)  When using VSDs, close attention to the grounding schemes is needed to avoid unwanted effects such as high-frequency bearing currents (caused by induced motor shaft and frame voltages), or to reduce the effects of EMI (electromagnetic interference).
  • Cable routing  Because of VSDs’ power electronics and the way that they operate, it is essential to consider carefully the routing of all cabling, otherwise other electronic equipment in their vicinity could suffer from interference. Any emissions which the motor cables produce can also affect other cables that are close by, even if they are screened, so product manuals recommend minimum distances from motor cables to other sensitive signals, to prevent “pick-up”. If cables need to cross, then crossing at 90 degrees is recommended.
  • Incorrect motor data and set-up  Once the power has been applied, it is important that the VSD is told the correct information about the motor to which it is connected. Without this, control anomalies will occur, the application will not perform correctly, and energy will be wasted. 

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