Welded Contact on a Star Delta
Welded Contact on a Star Delta
(OP)
With a 3-phase star Delta motor , with three contactors.
Does anybody know what will happen if one of the contactors welds shut.
Essentially there will be a voltage supplied to one side of the windings.
I am having a discussion whether the contactors on both sides of the winding is sufficent for a redundant shutdown( this is for a safety EN 13849-1 applications)
If once contact welds, I may have 230V AC on each side of the winding, but that is 0V Across it.
My own view, IS that I would prefer to have an extra contact, that will remove the voltage from each side of the winding, but this arrangements can be considered redundant.
Does anybody know what will happen if one of the contactors welds shut.
Essentially there will be a voltage supplied to one side of the windings.
I am having a discussion whether the contactors on both sides of the winding is sufficent for a redundant shutdown( this is for a safety EN 13849-1 applications)
If once contact welds, I may have 230V AC on each side of the winding, but that is 0V Across it.
My own view, IS that I would prefer to have an extra contact, that will remove the voltage from each side of the winding, but this arrangements can be considered redundant.





RE: Welded Contact on a Star Delta
If you are concerned about this, why are you using Star-Delta at all? If a welded contactor were a critical concern, I would get rid of the Star-Delta scheme (since it is very prone to such occurrances) and use a Solid State Starter with an isolation contactor. The chances of that contactor ever welding are astronomically small but it provides the added safety of protection against a shorted SCR.
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RE: Welded Contact on a Star Delta
They key question at hand is does the use of the K1,K2,K3( line Star and Delta) contactors, mwwt the requirements of EN ISO 13849-1. Typically Machinery builders will take the cheapest approach.
As this functin requires a redundant shutdown of the morot, I reccomended a 4th contactor which would cut power to both the line and star.Delta side. But machine builders typically do not want to do this.
to meet that I require redundancy, and I have talked to some experts in this area and they have differing views. The most common one is to say that it does not comply, but when chalenged to explain why then they cannot give a reason.
the key requirement is that a single fault will not cause a failure of the safety functions. To consider the case wher the line contactor welds but the power Star and delta open, then does the voltage not present at the winding constitut a failure of the safety function? Well the motor will not move , unless a current path is present, and an earth fault could supply this, though that is a second fault.
RE: Welded Contact on a Star Delta
RE: Welded Contact on a Star Delta
RE: Welded Contact on a Star Delta
You can build a control wiring scheme that would allow the motor to be stopped by the wye and delta contactors even if the main contactor welds.
RE: Welded Contact on a Star Delta
RE: Welded Contact on a Star Delta
cheapexpensive & nasty contactor melted and caused the moving poles to move away from the fixed poles. It's slightly un-nerving when the motor won't stop in response to an e-stop!