We replaced three contractors (Main, Delta and Star) and an OLR (Old OLR was not resetting and it looks like the links are completely melted during short circuit) We didn't find the exact problem but will mention what we did.
RE: Contactor getting welded when shifting from Star to Delta itsmoked (Electrical) 20 Feb 15 08:12 Or, are you still looking for other brands of "special" SD starter timer in your location. Please share your experience if the problem is resolved. The time-delay timer is the only culprit. If the Star and the Delta contactors are of different sizes, standard mechanical interlocking device from the contactor manufacturer may not be readily available. These two contactors must not be in the closed condition simultaneously, even momentarily. It is desirable to have mechanical interlock between the Star and the Delta contactors. Usually the Main and the Delta contactors are of the same size (current rating) whereas the Star contactor is usually selected one size lower. In Singapore, with hundreds of thousands of LV SD starters currently in use none of them is installed with mechanical interlock, interlocking all three the Main, Star and Delta contactors. RE: Contactor getting welded when shifting from Star to Delta waross (Electrical) 15 Feb 15 13:37 "You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" - Booker T. If it doesn't, you might try tossing that dinosaur and getting a modern soft starter.
#STAR DELTA PROBLEM PDF FREE#
The pounding that your drive chain has been taking all these years has taken a toll on everything and the juxtaposition of all of these elements is no longer allowing for any tolerance.Īs Gunnar said, the phase angle change (called "rolling") MIGHT help, and it's free other than your time.
#STAR DELTA PROBLEM PDF PLUS#
Why now after years of being OK? The effect is partially the result of residual magnetism in the motor, plus the phase angles of the sine waves at the exact moment of transition and howuch the rotor slows down as the open transition starter waits. It has been pundinf your motor and drive train components with torque spikes too. And by the way, what you have now witnessed as a catastrophic failure in the contractors is just the tip of the iceberg, the "weakest link" so to speak. That's it, but then it comes with there inherent risks. The ONLY benefit it offers is that it is slightly less expensive than a solid state soft starter. This is the main reason that I NEVER recommend Star-Delta starting methods. RE: Contactor getting welded when shifting from Star to Delta waross (Electrical) 13 Feb 15 12:59
Make the time long enough to allow the rotor field to decay. The other one is to introduce a delay between wye out and delta in. The phase 'drift' then will change and, if you are lucky, to the better. The simple one is to change phase sequence to the starter and then, to maintain motor rotation, change phase to the motor. What phase they are in is a result of phase sequence and the tiny time difference between wye contactor out and delta contactor in. If the voltages are in the wrong phase, then the contactor welds. It is the well-known fact that the rotor has a frozen magnetic field which induces an EMF in the stator winding and that the EMF hasn't decayed when the delta contactor switches. RE: Contactor getting welded when shifting from Star to Delta Skogsgurra (Electrical) 13 Feb 15 10:53 I have attached the photographs of the timers.īut before concluding let me know whether I am right about the timers or is there anything else I should be looking in to ? I do not want to make a mistake again. I would like to get more comments and somebody please help me to set these relay timers because I have no idea. (I am not referring to the long time taken to shift from star to delta while the motor gains its inertia.) The fraction of time taken to shift from star to delta is negligibly small causing a short circuit. What we suspect now is we have a faulty timer. We thought we had a faulty contactor since the machine is too old, So the star contactor could have stuck during the transition to delta causing a short circuit and it welded the links of all the three contactor that was in use during star delta transition.Īfter changing all the 3 contractor and also the 4th contractor for reversing, the motor was okay in a few trials and we run the motor for a while and we thought the problem is solved and we had a tea break and to our surprise when we started the motor after the break the exact problem repeats. When the 10 HP 420V 50Hz motor of my lathe machine gets shifted from Star to Delta all three contactors (Main, Star and Delta) gets welded and it trips my workshop supply altogether.
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