I used to test the standby power generator at the Peoria IL Police Dept on load, and would ramp the speed up and down, cuasing the frequency to be at 57-63 cycles for a period of time.
I took out several Air Conditioning Compressor motors, a couple of small muffin fans, and a couple of motors in the 20 channel logging recorders. We tested once a month. The A/C guy figured it out, that whenever a motor smoked, I was there running the generator. On rare occasions, other techs ran the generator, but didn't understand the raise/lower switch, so the didn't touch it, and they didn't burn out any motors.