Motor starting problem
Motor starting problem
(OP)
Hi,
We have installed a new star/delta starter panel for a 185KW motor which drives a compressor. Occasionally the main breaker trips on the transition from star to delta. We have experimented with the timer to try and achieve the optimum time to lessen the current and voltage effects on changeover. Any other tips would be helpful as we still seem to be having a problem. The loading of the compressor is timed after the motor has changed over to delta.
We have installed a new star/delta starter panel for a 185KW motor which drives a compressor. Occasionally the main breaker trips on the transition from star to delta. We have experimented with the timer to try and achieve the optimum time to lessen the current and voltage effects on changeover. Any other tips would be helpful as we still seem to be having a problem. The loading of the compressor is timed after the motor has changed over to delta.





RE: Motor starting problem
RE: Motor starting problem
As long as there is no fault in the motor,the setting can be increased.
subramanain
RE: Motor starting problem
RE: Motor starting problem
Do a keyword search of this forum on "Y Delta transition spike" , you will find that this has been discussed in detail many times. The condensed version is that this is very common, and has to do with the fact that most star/delta (Y-Delta) starters are open transition, and that introduces a transition spike that can be high enough to trip circuit breakers, blow fuses and even sometimes break motor shafts. The answer is to go with a closed transition starter, which is expensive, complicated and requires resistors, or change to a solid state soft starter.
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Motor starting problem
RE: Motor starting problem
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: Motor starting problem
RE: Motor starting problem
RE: Motor starting problem
RE: Motor starting problem
Does the compressor have a lot of inertia? Is it reasonable to try a start with the belts off?
RE: Motor starting problem
The magnetic or instantaneous trip for many circuit breakers is around 12 times the base rating. Therefore if the motor has an LRC greater than 6 times FLC, nuisance tripping can be expected.
Hope the above assists you to make a decision on your best way forward.
Regards,
GGOSS
RE: Motor starting problem
RE: Motor starting problem
A common problem with star/delta starters, in addition to the transition transients, is that often the torque available in star is not sufficient to accelerate the motor and load to full speed so the transition accurs at less than full speed. If the transition occurs below 85% speed, then the current will be close to LRA until the motor reaches around 85% speed when the current will begin to fall away. Actual values of current and speeds are very motor and load dependent, but the majority of star delta starters that I have seen do not achieve a worthwhile reduction in current because the torque in star can not get the load to full speed before the transition.
Best regards,
Mark Empson
http://www.lmphotonics.com