September 2007 Electrical Apparatus

September 2007 Electrical Apparatus

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

We think of a global marketplace as one in which the same goods, made to the same standards, are sold worldwide. Although that applies to many consumer goods, the approach to efficiency standards for industrial electric motors is broadly diverse. Government agencies and environmental groups issue an increasing variety of requirements.

Improving motor efficiency is simple in theory. What’s uncertain is how far such improvement can cost-effectively go. That depends upon the economics of manufacturing and energy sources in each country. Within the European Union, several agencies now prescribe motor efficiency levels, among them CEMEP (a motor manufacturer group) and the SEEEM program sponsored by utility, government, and industry organizations. Elsewhere, standards in China, Japan, Australia, the United States, and Canada have been adopted to dictate efficiencies at several levels or grades, for standard machines, mostly of low voltage ratings at 2, 4, and 6 pole speeds (sometimes including 8 poles).

Some requirements are guidelines only; others are subject to legal enforcement. In either event, motor users must be able to rely on the accuracy of the manufacturer’s stated efficiency when making purchasing decisions. Unfortunately, little progress has been made towards a single universally accepted global standard for verifying motor efficiency by test.

The problem is stray load loss. No simple test measures it directly. In the United States, load testing plus statistical analysis using IEEE Standard 112 Method B has been incorporated into federal law. In Europe, under IEC 60034-2, stray loss has been arbitrarily assigned a single fixed percentage of power input for all motor ratings. However, IEC 61972 was recently adopted to allow either the method of IEEE 112, or a varying percentage of output, and IEC 60034-2 is now being revised to add yet another option for stray loss evaluation. In some countries, prescribed efficiencies depend upon which test is used.

Add to that the accommodation for both 50 Hz and 60 Hz designs, plus the widespread system of output rating in kilowatts instead of horsepower, and the motor user clearly faces increasing difficulty in deciding what to believe. No simple solution appears to be forthcoming soon.

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