October 2007 Electrical Apparatus

October 2007 Electrical Apparatus

This is a summary of the Electrical Apparatus October 2007 featured technical article, by Richard L. Nailen, P.E.    

The energy-saving and operating flexibility benefits of electronic adjustable-speed control of a-c motors have brought users inconveniences as well. Some can be serious problems with medium-voltage apparatus in sizes above a few hundred kilowatts.

First, premature equipment failures can cripple a continuous process industry. Second, advances in complex electronic technology can render both hardware and software obsolete within a few years. Replacement parts for older units become difficult to get. The retraining and re-programming needed for the transition to newer apparatus can cause costly downtime.

Seven years ago, petrochemical engineers within the IEEE decided that a standard was needed to enable drive purchasers to deal with such concerns. The result, published in 2006, is IEEE Standard 1566 for “Performance of Adjustable Speed AC Drives Rated 375 kW and Larger,” and covering only ratings of 750 volts and above. The scope involves the entire drive system consisting of switchgear, input transformer if any, controls, bypass, and motor (either induction or synchronous). Compatibility between drive and motor is assured by vesting total system responsibility in a single vendor.

While placing no restrictions on basic drive topology, the standard presents detailed requirements for drive enclosure (such as the ability to contain a bolted fault); installation; grounding and bonding; solid-state component ratings and cooling; loading capability; harmonic generation; behavior during utility supply disturbances including voltage sags, swells, and transient surges; control, alarm, and protective functions; testing; startup; and safety.

In addition, IEEE 1566 stresses the need for reliability, and dictates minimum service life. The vendor must identify those replacement parts needed to maintain that life, make adequate technical support available throughout that life, and must furnish expected values of mean time between failures and mean time to repair “based on known experience.”

Appended to the text are data sheets allowing both purchaser and vendor to describe any changes or variations specific to a particular application.

To order a back issue with the full article, “A new standard for large drives” call 312-321-9440 or visit our online webstore.

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