How do manufacturers determine the 'rated' quantities for motors?

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Discussion Overview

The discussion revolves around the concept of "rated" quantities for motors, exploring how manufacturers determine these ratings and what they signify. Participants examine the implications of these ratings in terms of maximum operational limits, safety margins, and tolerances, as well as the continuous operation parameters defined by standards.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses confusion about the term "rated" and questions whether it refers to maximum limits, particularly in relation to heat and temperature, while seeking reliable sources on the topic.
  • Another participant references IEEE standards, indicating that "rating" describes the continuous operational design of equipment, specifically mentioning voltage ratings and the conditions under which these ratings apply.
  • A participant questions the notion of maximum ratings, suggesting that while motors typically have maximum ratings for various parameters, they may also have minimum ratings for aspects like temperature and speed.
  • It is noted that the 'Rating' indicates the operational region where a motor is expected to meet its lifetime expectations, with an analogy provided about bicycle speed ratings to illustrate the concept of operational limits.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the definition of "rated" quantities, as there are varying interpretations regarding maximum and minimum ratings and their implications for motor operation.

Contextual Notes

Some participants highlight the potential for confusion regarding the terminology and the need for clarity on safety margins and tolerances in the context of motor ratings.

Who May Find This Useful

This discussion may be of interest to individuals involved in engineering, manufacturing, or those studying electrical and mechanical systems, particularly in relation to motor specifications and standards.

yucheng
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I'm confused with the term "rated". I checked this webpage though I am not confident about it's reliability.

Context: Motor ratings etc.

Does it mean maximum? Maximum in what regard? Heat produced/temperature? Is there a more reliable source on how manufacturers determine the 'rated' quantities? Does it take into account safety margins, tolerances etc? (I might be jumbling jargon!)
 
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I did some searching in the IEEE standards. They describe "rating" as what the equipment is designed to operate at continuously. I would link to it so you could read it, but it requires a login.

An example of voltage rating:

Maximum design voltage-to-ground: The maximum steady-state voltage-to-ground at which the high-voltage cable termination is designed to operate continuously under normal conditions.
NOTE—It is not intended that this maximum voltage limit be applied to transient overvoltages or unusual service operating conditions where the system voltage may exceed these values for only short periods of time.
 
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scottdave said:
They describe "rating" as what the equipment is designed to operate at continuously.
Maximum?
 
yucheng said:
Maximum?
Usually, but not necessarily.
A motor would have maximums for Voltage, Load, Temperature; it could also have minimum ratings for Temperature and Speed.

The 'Rating' is the operating region where the motor will meet its expected lifetime when the rest of the 'Ratings' are approximately met..

For instance a bicycle may be rated for a speed of 25mph (40kph). You can operate it slower, but at some low speed it gets so difficult to balance it falls over.

At a higher speed of 50mph (80kph) the front wheel may start to shake or the brakes may overheat and fail at a sudden stop.

Hope this helps!

Cheers,
Tom
 
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