Apparently, my colleague who asked me to consult on this issue did not have the entire story. The problem is not so much the HP rating of the installed motor. Rather, the larger motor came with a different set of speed reduction gearing. The resulting rate at which the gate will be lifted or lowered will be on the order of 45 times faster than originally designed. A VFD should be able to help with that problem, should it not?
This can’t easily be fixed for a couple reasons.
You have 10 times the torque but then geared down by 1:45 so torque is now 10/45 or about 1/5th of the original but it sure sounds like a typical “gate motor” so probably acceptable from the gate company and works fine, just very fast. Sometimes procurement with those companies can be SLOW though.
Which brings up the problem. This is what we call a constant torque load. And it’s probably a custom motor. On NEMA motors when run near their design torque you can run them down to about half speed (50%). After that the fan is now at 1/4 of the cooling (fan CFM is square of speed) so even though Horsepower is half what it was fan cooling dropped even faster. So the motor is in danger of burning up unless it doesn’t get run very long for very often (duty cycle) and again probably difficult or impossible to get full motor specs from the company that wants to sell you the proper gear motor and not mess with hack jobs and possible warranty claims.
And finally at under 2-3 Hz control over the motor becomes a problem. You are getting close to the point where the drive output begins to look like DC. Flux vector doesn’t work. I’m assuming encoder control might be impossible (buying another motor) despite being your best option and V/Hz is notoriously finicky. So control is going to be a huge problem if it doesn’t burn up first.
Also those gate motors tend to be high torque so slip is low which compounds your control issues.