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I have seen some induction motors have information on their nameplate listed for 50hz and 60hz. While I've read a requirement that the Voltage/Frequency ratio be consistent, using these nameplate numbers you can come up with examples like 380V/50Hz = 7.6, and 440V/60Hz = 7.33. These are not the same. Are they close enough that it doesn't matter? Does this mean all induction motors can be run in either frequency? All 3 phase induction motors can be run at either frequency? Only motors designed used in at both frequencies?

Edit: I see the nameplates. I'd just like to have an idea of why - I'll take any direction you can point me in. Did marketing de-rate these motors so they can run slow enough or cool enough at either frequency? Did accounting let them use better materials? Do I need to take a graduate level FEM course in order to understand, and I'm asking the equivalent of how to measure the current across and the voltage through?

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  • \$\begingroup\$ "ratios need to be consistent": for what? For what kind of induction motor specifically? You might be overgeneralizing something there! \$\endgroup\$ Mar 17, 2021 at 21:24
  • \$\begingroup\$ “Some” does not mean “all” as in, if some snakes are venomous are all snakes venomous. Read the nameplate for each snake. \$\endgroup\$
    – Andy aka
    Mar 17, 2021 at 21:33
  • \$\begingroup\$ @MarcusMüller I most likely am overgeneralizing! When trying to find this answer, I see a few questions on forums asking if people can use a 50Hz motor on a 60Hz system (or the opposite). This 'ratio' seems to be a common response. While that's not a very credible citation, I do see it come up in a lot of "How VFDs work" Example source: vfds.com/blog/motor-theory-101-adjusting-frequency \$\endgroup\$ Mar 17, 2021 at 21:35
  • \$\begingroup\$ @Andyaka If it isn't too broad to ask what goes into the design of a motor that works at both 50Hz and 60Hz, I'd much rather ask that. I'm hoping to settle for something like 'No single phase CSIR will ever be dual phase, but all 3-phase squirrel cage induction motors can'. [warranty voided if used off label] -Or any rule of thumb. \$\endgroup\$ Mar 17, 2021 at 21:41
  • \$\begingroup\$ @MarcusMüller, I'm interested in AC motors. Asynchronous, 3-phase squirrel cage or wound rotor, and if there are any single phase motors, such as PSC or shaded pole. Perhaps universal motors? \$\endgroup\$ Mar 17, 2021 at 21:45

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The volts/hertz ratio must be constant within some limit. Only the manufacturer can state that limit. Some manufacturers mark something on the nameplate like 380/440 V 50/60 Hz. That is 7.67/7.33 V/Hz or 7.5 V/Hz +/-1.7%. Marking it on the nameplate is essentially the manufacturer's guarantee that is ok for that particular motor. It is likely that you can operate motors marked only with one frequency or the other at something within a couple of percent of the same V/Hz. There is probably not much risk in doing that, particularly if the motor is not running at rated torque 24/7.

With constant V/Hz, an induction motor should be capable of operating at rated torque over a range of speeds while drawing rated current.

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  • \$\begingroup\$ Thank you. Would it be reasonable to say that they designe towards for a target and then firm up those numbers in the reliability testing stage? \$\endgroup\$ Mar 17, 2021 at 22:13
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    \$\begingroup\$ I would not call it a "reliability" testing stage. It is more of a design verification test. \$\endgroup\$
    – Gone Off
    Mar 17, 2021 at 22:18
  • \$\begingroup\$ Awesome. Thanks. \$\endgroup\$ Mar 17, 2021 at 23:57

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