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And why exceeding standards may not be a good idea
LIBERAL VERSUS CONSERVAuve. In politics we think we know what those terms mean. Though not always accurate, the stereotypes are wellknown. A "conservative" follows the old ways; honors tradition; avoids the new, the untried, the risky. The "liberal" is ready to take a chance, to adopt new ideas, to "think outside the box."
In electric motor manufacture, however, how do we describe the design for performance that exceeds standards, that goes beyond the nameplate rating, that offers the user a greater margin for uncertainty in the application? We tend to call that "conservative" design - yet such an approach invariably involves more "liberal" use of material and labor.
Not only does the meaning of the terms become fuzzy; the value of such "overdesign" is open to question. How exactly is it to be done, and what specific benefits can be expected? In line with the political definition, users seem to expect that conservative design will result in a motor "being built the way they used to be" in some past era, when motors "would hold up better than they do now."
That's not a new idea. Consider this comment made during a nationwide survey of motor users: ". . . most [motors] are getting cheaper, less able to overload, poorer frames, weaker insulation." A comment from the year 2000, from 1980, or 1960? No, way back in 1952.
Consider the opinion of one user as quoted in a 2008 report from the Electrical Apparatus Service Association on the state of die service industry. "He said the new premium efficient motors ... no longer have the extra mass in many of the parts" mat presumably made older motors last longer in abusive applications.
That "extra mass" (in what parts, or how much extra, he didn't say) might not be welcome in his automobile, with die consequent reduction in fuel economy. More important, he offered no specifics about the expected benefit of extra motor mass. No body of hard data supports the belief that simply adding "more mass" materially increases Mean Time Between Failures (MTBF).
Besides the standards of NEMA or the IEEE, what guides the motor designer? Only two things: past experience (tests, manufacturing...