Converting wound rotor motors to squirrel cage
Converting wound rotor motors to squirrel cage
(OP)
Hi all,
Came across this scenario a few weeks back. Customer's plan was to convert some old wound rotor motors on liquid rheostats to a squirrel cage mimic on soft starters. So we short out the windings in the motors terminal box and hook them up to a soft starter. Hey presto! we start them and they just sit there humming....So I do a little research online and discover a few bits and pieces suggesting this isn't a good idea due to the fact wound rotors have inherently low torque for a motor when they aren't tuned with their rotor resistors (shorted) and the fact we are applying a lower voltage through the soft starter lead to a really low starting torque. Now my question is: is it purely the low torque preventing the motors from going? As by chance one of our converted motors didn't have a load so a brave electrician gave it a pre-spin before I ran the soft starter and it went like normal...then we stopped it and ran it again and it ran once more and finally we ran it another time to be sure and it went back to humming. So is there other factors at play here like alignment of slots within the motor. If you understood this and have an idea I would love to hear?
Thanks,
Luke
Came across this scenario a few weeks back. Customer's plan was to convert some old wound rotor motors on liquid rheostats to a squirrel cage mimic on soft starters. So we short out the windings in the motors terminal box and hook them up to a soft starter. Hey presto! we start them and they just sit there humming....So I do a little research online and discover a few bits and pieces suggesting this isn't a good idea due to the fact wound rotors have inherently low torque for a motor when they aren't tuned with their rotor resistors (shorted) and the fact we are applying a lower voltage through the soft starter lead to a really low starting torque. Now my question is: is it purely the low torque preventing the motors from going? As by chance one of our converted motors didn't have a load so a brave electrician gave it a pre-spin before I ran the soft starter and it went like normal...then we stopped it and ran it again and it ran once more and finally we ran it another time to be sure and it went back to humming. So is there other factors at play here like alignment of slots within the motor. If you understood this and have an idea I would love to hear?
Thanks,
Luke





RE: Converting wound rotor motors to squirrel cage
RE: Converting wound rotor motors to squirrel cage
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Converting wound rotor motors to squirrel cage
RE: Converting wound rotor motors to squirrel cage
That said, a VFD is a better option than a soft starter in such cases of conversion.
Muthu
www.edison.co.in
RE: Converting wound rotor motors to squirrel cage
RE: Converting wound rotor motors to squirrel cage
Muthu
www.edison.co.in
RE: Converting wound rotor motors to squirrel cage
RE: Converting wound rotor motors to squirrel cage
http://winding.wix.com/design
RE: Converting wound rotor motors to squirrel cage
Has your customer considered a resistor bank and contactors to replace the liquid rheostats? 75 kW is well within the range of resistor starters for wound rotor motors.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Converting wound rotor motors to squirrel cage
RE: Converting wound rotor motors to squirrel cage
RE: Converting wound rotor motors to squirrel cage
RE: Converting wound rotor motors to squirrel cage
RE: Converting wound rotor motors to squirrel cage
http://www.lmphotonics.com/slipring.htm
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