advanced search

Troubleshooting VFD Problems

Nov 1, 2000 12:00 PM, By Paul Frank

Find more articles on: Variable Frequency Drives

When a motor drive goes down, production often grinds to a halt. How do you find and resolve the problem quickly?

When that variable frequency drive (VFD) goes down, you're under pressure to get it back online. Don't let this pressure make you take even longer to resolve the problem. Instead, remember the VFD troubleshooting checkpoints: check the basics (the controller display, connections, and temperatures), check the motor, and check the drive - then check a little closer.

Check the controller display. Most VFD controllers include an interface to set up the drive for operation and to display information about its operation, once it's underway. Although the information displayed varies, most controllers tell you about high current (usually including blown fuses and overload trips), high and low voltages on the input and output sides, high temperatures, internal faults, and even offer advanced power diagnostics.

Check the connections. If the fault codes can't help you track down the problem, then check the connections. Loose connections are among the most common causes of faulty operation in VFD applications. Just eyeballing a connection is sometimes enough to know it's loose. You can also check for a voltage drop across the connection if you're still powered up - or resistance through a connection if you're powered down. Don't forget to isolate the connection to get a reliable reading.

Check temperatures. Checking the temperature of connections with a temperature probe or IR-thermometer is one way to tell if they're loose. They should never be hotter than the connecting wires. You can check temperatures in the drive and at the motor. For example, if the motor insulation is unsuitable for VFDs, it'll gradually degrade until it develops a short. Such shorts are often too small to blow a fuse, and too intermittent to trip an overload - but enough to shut down a controller. An IR thermometer can show what's going on. Also, use your nose: If a motor smells hot, it is.

You can do more. But usually, just checking the basics will be enough to uncover any problems you may have and get the system running again. That can give you the time you need for a permanent fix.

Sidebar: Check a Little Closer

In new installations, apparent problems with drive performance are often due to improper application, drive selection, setup, or installation of the motor as well as the drive. Sometimes "drive problems" are due to process control logic and not the drive at all.

In the case of frequent breaker trips, you may need to examine protection coordination, to ensure your breakers are the right size from the drive back to the service. You may also need to check other branch and feeder circuits. But first, see if your drive can reduce inrush current with a "soft start" function. Also, you may need to check:

- Current to the motor (ammeter),

- Voltage notching (oscilloscope),

- Inductive noise in signal, control, or power wiring (oscilloscope),

- Cable routing (visual inspection),

- Damaged signal, control, or power wiring (insulation resistance, TDR), and

- Current through the controller during sudden load changes, or during speed ramps (controller display).

Want to use this article? Click here for options!

© 2012 Penton Business Media, Inc.

---

Acceptable Use Policy blog comments powered by Disqus

Browse Back Issues Select an Issue November 2011 October 2011 September 2011 August 2011 July 2011 June 2011 May 2011 April 2011 March 2011 February 2011 January 2011 December 2010 November 2010 October 2010 September 2010 August 2010 July 2010 June 2010 May 2010 April 2010 March 2010 February 2010 January 2010 December 2009 November 2009 October 2009 September 2009 August 2009 July 2009 June 2009 May 2009 April 2009 March 2009 February 2009 January 1, 2009 December 2008 November 2008 October 1, 2008 September 2008 August 2008 July 2008 June 1, 2008 May 2008 April 2008 March 2008 February 2008 January 2008 December 2007 November 2007 October 2007 September 2007 August 2007 July 2007 June 2007 May 2007 April 2007 March 2007 February 2007 January 2007 December 2006 November 2006 October 2006 September 2006 August 2006 July 2006 June 1, 2006 May 1, 2006 April 2006 March 1, 2006 February 2006 January 2006 December 2005 November 2005 October 2005 September 2005 August 2005 July 2005 June 2005 May 2005 April 2005 March 2005 February 2005 January 2005 December 2004 November 2004 October 2004 September 2004 August 2004 July 2004 June 2004 May 2004 April 2004 March 2004 February 1, 2004 January 1, 2004 December 1, 2003 November 1, 2003 October 1, 2003 September 1, 2003 August 1, 2003 July 1, 2003 June 1, 2003 May 1, 2003 April 1, 2003 March 1, 2003 February 1, 2003 January 1, 2003 December 1, 2002 November 1, 2002 October 1, 2002 September 1, 2002 August 1, 2002 July 1, 2002 June 1, 2002 May 1, 2002 April 1, 2002 March 1, 2002 February 1, 2002 January 1, 2002 December 1, 2001 November 1, 2001 October 1, 2001 September 1, 2001 August 1, 2001 July 1, 2001 June 1, 2001 May 1, 2001 April 1, 2001 March 1, 2001 February 1, 2001 February 1, 1995 January 1, 2001 December 1, 2000 November 1, 2000 October 1, 2000 September 1, 2000 August 1, 2000 July 1, 2000 June 1, 2000 May 1, 2000 April 1, 2000 March 1, 2000 February 1, 2000 January 1, 2000 December 1, 1999 November 1, 1999 October 1, 1999 September 1, 1999 August 1, 1999 July 1, 1999 June 1, 1999 May 1, 1999 April 1, 1999 March 1, 1999 February 1, 1999 January 1, 1999 December 1, 1998 November 1, 1998 October 1, 1998 September 1, 1998 August 1, 1998 July 1, 1998 June 1, 1998 May 1, 1998 April 1, 1998 March 1, 1998 February 1, 1998 January 1, 1998 December 1, 1997 November 1, 1997 December 1, 1996 November 1, 1996 October 1, 1996 September 1, 1996 August 1, 1996 July 1, 1996 June 1, 1996 May 1, 1996 April 1, 1996 March 1, 1996 February 1, 1996 January 1, 1996 December 1, 1995 November 30, 1995 November 1, 1995 October 1, 1995 September 1, 1995 August 1, 1995 July 1, 1995 June 1, 1995 May 1, 1995 April 1, 1995 March 1, 1995

browse e-newsletters