Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Control torque of 3 phase motor

  1. Oct 22, 2013 #1
    Dear all,

    This is a newbie asking for some information.

    Actually, we have 1x30HP, 2x10HP motors working at our workplace. When we start the motors there is a lot of torque generated due to which our grid supply charges us penalty every month.

    We need information about the device(s) that are used to control the torque.

    While doing some research, I got to know that I can get myself set up control panel that has capacitors either separately on each motor or on my 100kva transformer. This will control the torque as well as give me saving on electricity bill.

    Kindly help in this regards.
  2. jcsd
  3. Oct 22, 2013 #2
    Hello ine...Welcome

    Not really torque- that is the physical output of the motor you are probably being charged for reactive power - KVAR or poor Power Factor (PF) on your bill. A common issues with these motors is they are oversized and this leads to the poor PF or too much Reactive Power.

    If the load on the motors is very consistent, then you can add capacitors, but this should be an engineered solution. It is also possible to get an automatic capacitor bank that adjusts - more engineering and $.

    Another solution would be to add variable speed drives - these will run the motors at the proper point to match the physical load - the advantage of this is they react to variable load very well, but also need to be engineered and can be expensive (10HP drive ~ $ 2500-3500 - plus install and set up) , but typically these will save energy and pay for themselves in a few years, especially if the physical load is much less than the rating of the motor.

    If you do not know of a good technical resource to help and advise - I would contact your utility to make a recommendation, they should make a site visit, prepare a basic sketch and discuss the possibilities - most utilities here in the US provide this service - since they are not selling the equipment, they SHOULD give you a fair assessment.
  4. Oct 23, 2013 #3
    Thanks a lot for the reply.

    I have researched about this in the local market and got to know that people have installed a device called Power Factor(A panel board which has capacitors). Good quality capacitors are from Hyundai or LG i heard.

    Many people have installed them with their transformers rather than on individual motor. For e.g you have 100 kva transformer, but people have installed Power Factors which can handle load of 200kva to carter any torque from motors etc.
    The power factor actually handles all the load of the workplace and includes all motors working.

    Other than that I have got information on Motor Soft Starters such as the one in the link below:-
  5. Oct 23, 2013 #4
    I believe the device would be a Power Factor Corrector - since Power Factor is the condition, not a device. If the added capacitors are on all of the time, and the motors are not, this can be detrimental to the motors when they start and other factors. -- while this may be a good solution, not something I would just throw on the system as a remedy.

    Also - a Motor Soft Stater, is a different device, but your link is for motor drives, so that does seem to be what I was suggesting. - again not a project for a novice.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook