That was just a typical example:
“Actually squirrel cage motors are asynchronous machines. For example a 50Hz motor at full load speed would run at 1485 rpm.”
The actual motor in my case was a six-pole unit. And yes it WAS squirrel cage machine with a variable speed drive.
It’s just routinely what we did.
@Bruce @Besoeker @realspeed @OldGreyFox ,
Jesus, You lot all seem to have different ideas how electric
motors work ??
I fort there were only two sorts of electricity ??
AC. and DC?? and l fort AC didn’t have slip rings, but DC did ??
Am l wrong ??
Donkeyman! 
I know when Husband had turned off the mains switch, was in the cupboard under the stairs with loads of Junk and coats on hooks and more junk…He then was able to take off the bulb holder and see what wire had maybe come loose…All went well, when suddenly be got a shock and had to fight to let go. Was like do or die.
One of the three young 'uns had gone in the cupboard under the stairs and flicked the switch back on. 
After that is had a lock put on it… 
@DianneWoollie , That is, or was, a large cause of deaths in
industry Dianne !!
Now we have safety rules and safety officers in all large
Industrial complexes, that ensure that isolators are locked out
and that prominent notices are hung on the switch !!
Your old man was lucky 
Donkeyman! 
That’s fine, it makes sense now you’ve clarified it. I was just interested.
He was very young then… 
also not normally got stick up hair either…
Well, yes AC and DC. But quite a few different motors.
DC motors mostly had commutators. Paper machines were a typical example. Accurate speed holding was requirement where maybe a dozen or so large cylinders were in tandem. When I mean large the the cylinders were up to 240 inches wide or more and the length was around 100 yards.
Now the paper machines have mostly been replaced by AC motors. They are simpler and more robust… The electronic controls are more complex but better devices has largely mitigated the complexity.
Then there are the different types of AC motors. The vast majority of them in industry are squirrel cage machines with basic fixed speed. But they are also used for variable speed applications. Water pumping stations are a typical where speed control is required. An interesting application is submersible pumps.
And then there other AC motors. These are wound rotor machines requiring speed control. We have used these for large fans (2,200kW) and compressors in petrochem plants
Then there are power stations. These are synchronous machines. The one’s I dealt with were 6600 MW.
