advanced search

What’s the Most Cost-Effective Way to Obtain 380V?

Oct 1, 1998 12:00 PM, Edited by Robert J. Lawrie

Q. A large textile plant purchased several looms from Europe, which operate on 380V, 3-phase. The only distribution voltage available is 480V, 3-phase. The plant requested advice on the most economical way to obtain 380V for these loads. The electrical service to these looms is from a 3-wire busway. The service to the plant is 480/277V, 3-phase, grounded wye.

I determined an autotransformer connected in open delta (no neutral) would be the most cost-effective arrangement. However, local jurisdiction told me this connection violates Sec. 210-9 of the NEC. I see how an autotransformer in an ungrounded wye system would cause problems, but why would an open (or closed) delta autotransformer create problems? Can anyone explain this to me? —N.K.

A. N.K. didn’t mention the circuit frequency for the looms. The frequency in UK is 50 Hz—in France it’s 331/3 Hz. These parameters were adapted in the channel tunnel projects a few years back. At one time, there were other variations in power sources in Europe. Perhaps they still exist.

The proposed solution is technically reasonable, but without details of the 380V, 3-phase system, it’s difficult to be sure. We once had a situation requiring application for 50 Hz in our 60 Hz arrangement. Our solution was to use a standard 60 Hz generator running at reduced speed to provide 50 Hz power. It worked. Perhaps N.K. could apply a similar solution to his situation. —B.B.B.

A. I recommend using a 3-phase transformer with a 480V delta primary and a 380Y/220V secondary. These are available for 60 Hz applications. As far as compliance with Sec. 210-9 of the NEC, the application would fall under one of the exceptions, since the grounded circuit conductor isn’t needed for supplying the loads. However, I assume the exceptions don’t list the specific voltage of 380V, since it’s rare in the U.S. —M.R.P.

A. N.K.’s reason for using an open-delta connected autotransformer scheme to change 480V, 3-phase to 380V or 400V, 3-phase is not appropriate. For example, the maximum kVA loading can’t be more than 58% of the bank’s total nameplate rating. If you exceed this limit, the transformers will overheat. Also, the current loading on the 3-phase, 480V primary system will be unbalanced on a per-phase basis. And, the 380V to 400V, 3-phase line-to-neutral voltages won’t be symmetrical, because the neutral “zero” point is determined by the original 480V supply. Because he would have to use two “custom” single-phase autotransformers, each rated 480V, with a tap at 380V or 400V, his plan would cost the same as a single “special” 3-phase transformer rated 480V delta to 380V or 400V wye. This latter type of transformer is usually obtainable from the larger manufacturers.

For either arrangement, N.K. would need primary and secondary overcurrent protection in accordance with the NEC. The European Union Electrical power utilization format is now 400VY/230V, 3-phase—it was 380VY/220V, 3-phase. This parameter is comparable to the U.S. practice of using 460V-rated equipment on a 480V supply. It is also important to verify these looms will correctly operate on 60 Hz power. Some minimally designed European electrical utilization systems will not work on other than 50 Hz. —F.M.P.

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