How does one set the stopped state cooling time of an induction motor without the datasheet providing that value? In some digital relays, there is a running cooling time (or rather running time constant entry), and also a separate entry for stopped cooling time. Since the shaft-connected fan or other forced cooling may be off when the motor stops, it is not uncommon for the stopped cooling time constant to be longer than the running time constant. The running time constant I'm able to get by coordinating thermal damage curves with the relay's protection curves. However, is there any rule of thumb, or some rough lookup option based on motor enclosure, voltage, HP, frame type etc. to roughly figure a cooling time/cooling time constant? Any reference/document you could point me to will be very helpful. This is if there are no Ambient RTDs being used (since some relays can use this to learn the cooling time).
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