My experience with motors and voltages
Why is some of my equipment rated for 440 volts while others are rated for 460 volts and still others rated for 480 volts three phase? My service is 277/480VAC but the power coming in is actually 500 volts!!!
Why is there such a disparity in the voltage ratings on different equipment? Same with 220/230/240VAC and 110/115/120VAC single phase. Why the different ratings?
In my experience voltages have risen over the decades because there has been more demand, which lowers the voltage on the transmission lines and from the transformers, I remember 208v Motors being the norm, then it went to 210, then 220, then 240.
It comes down to money, doesn't everything?, specifically cutting power loss where the utility companies are concerned, transmission and transformer (loss of electricity) is lower at higher voltages. So in short, transmitting electricity at higher voltages, saves the Utility companies money.
Most industrial 3 phase motors are internally wired for the higher voltage range 440,460,480, they are usually more efficient at higher voltages than when wired in the 208, 210 220, 240v low range.
Higher voltage windings are heavier and provide more inductive power so they are less likely to lag with increased load, increased load raises current flow as voltage drops.
As voltage drops and current increases more energy is turning to heat in the windings instead of inductive magnetic power to the shaft.
I have 247 volts at my outlet right now, but I would have no problem running a 208v motor with this over 18% increase in voltage. I will be drawing less amperage at 247v which equals to transmitting less heat into the windings.
I have a Cincinnati Mill it is rated at 480v, I would want to consider heat if running a lower voltage to it like 440 because if I load the machine down it is more likely to lag and trip the overload drawing higher amps through the heaters in the overload.
Everything in life is relative, you can have 2 cars each towing a trailer one has a larger motor, as they both go down a level road both have no problem with horsepower to do the job but when they come to a hill the car with the smaller motor will have to work harder to keep up, which will generate more heat and more drag or lag on the motor and it might overheat. Loading an electric motor down with a lower voltage power applied increases the heat in the motor windings breaking down the insulation which over time if it continues will destroy the motor
Like with welders, comparing them to motors, some are heavy duty, they use more copper in the windings to make them stronger, in a welder it is called duty cycle, that is how long you can continuously weld without overheating the windings. A heavy duty motor will have more tolerance to overheating as voltage drops but it is still a concern when you are loading it down.
I have yet to see a motor burn up with a higher voltage within the high voltage range 440, 460, or 480, it is lower voltage than what is rated that can destroy them. When you slow the shaft down with load and the voltage is lower, the motor has less power to keep up with the RPM the frequency wants the motor to turn, when this occurs more heat is generated in the windings and less into magnetic power in the windings.
I can probably easily run my Cincinnati 480V mill at 440 or 460volts, but I would have to watch the load I was putting on the machine, because the heat and amperage draw will increase at lower voltages.
Motor lag, which is the amperage leading the voltage increases with load, this increases motor winding heat, just like a motor in an underpowered car pulling a trailer up a hill.
If you want to get technical and you are into math, read this link and it explains things relative to motors and electricity, it gets very complicated more than I have time to study.
Motors are usually protected from heat, but if they overheat once you better find the problem.... because each time they overheat, the insulation in the windings breaks down and the more it breaks down, the more electricity flowing into the motor turns to heat instead of power to the shaft, it will eventually come to a point where it loses all power and will not start and instead just create heat or burn up.
The break down of the motor winding insulation allows electricity to flow across the windings instead of through the wire of the winding which decreases the induction of the magnetic field that gives the motor it's power to start and run, if it does not start it has 100% lag and becomes a heater burning up or tripping out the overload.
The link below gets into detail more than I care to know, common sense and experience sometimes is better than book smart.
https://www.me.ua.edu/me416/LECTURE MATERIALS/MotorEffic&PF-CM5.pdf