Anyone ever heard of this??

[mull982]

Recently in my plant all of our size 5 480V Siemens/Furnas motor starters have failed. About a month ago all of these starters (about 5 of them) started chattering uncontrollably until they are eventually failing one by one. When they fail, they are not able to hold the contact in.

It strikes me as strange that these starters have been in service working fine for a number of years and then all of the sudden they all start to fail at the same time. All of these starters are on different MCC's throughout the plant. We have many other size starters (1-4) that are working fine and do not exibhit this problem. The only thing that I can think that is different with the size 5 starter then the rest is the fact that they use an 480V coil.

Anyone ever heard of anything that can cause this problem?

 

[zog]

Bad CPT? Have you done any troubleshooting?

 

[LarryFine]

Have you checked voltage at the coils?

 

[mull982]

Yes we checked the voltage at the coils and they were all at around 480V or within tolerence. However on one of the starters the coil read about 10% low at about 435V. Like I said all of the other starter coil voltages read fine except for the one however they all exibhited the same type of problem.

Woul a voltage lower thatn the rated 480V cause damage to these contactors? How about higher voltage?

 

[76nemo]

Yes we checked the voltage at the coils and they were all at around 480V or within tolerence. However on one of the starters the coil read about 10% low at about 435V. Like I said all of the other starter coil voltages read fine except for the one however they all exibhited the same type of problem.

Woul a voltage lower thatn the rated 480V cause damage to these contactors? How about higher voltage?

It's when your AC gets dragged down that can cause them to chatter. Interesting problem, keep us informed

 

[wirenut1980]

It sounds like the contactors are seeing low voltage, low enough and for a long enough time that they are pulling apart and then closing back in, repeating until they get worn out. Hard to say whether the voltage sags are caused by short time events out on the utility line or, events in your plant, or a low RMS supply. If possible, monitor the voltage at the common point of all the contactor failures, i.e whatever bus they are all fed from. Your utility might be able to help you by monitoring at the PCC or transformer and at least see if you are getting low voltage and can compare with your readings.

Sags can be hard to capture unless you have a monitoring device to store the measurements over an extended period of time.

 

[beanland]

Inside or Outside

Inside or Outside

Voltage sags are the most likely cause of the contactors chattering. Has anything new been added in the plant that could be causing the voltage to drop? Some intermittant load? Spot welding station? Hammer mill? Crusher? Something with fluctuating load. Has anything happened on the utility side where they are having low voltages?

 

[jrannis]

Cant say Im a big fan of using 480 for controls. I have chased ghosts for many hours dealing with backfeeds people have setup over the years. Any possibility that maybe a new or large load was introduced into your plant or something. I think you mentioned that the control circuit originated at each individual MCC? Sounds like a low voltage problem.

 

[ptonsparky]

What controls the coil? Does it come through another relay operated at a different voltage? Check that control circuit.

 

[brian john]

We had a customer that was constantly losing coils. Also 480 VAC controls, it was a low voltage issue, did not affect the motors (may have shortened the life in the long run). The coils fried and in several cases smoked so bad the NEMA 4 starters had to be replaced. No small expense.

This happened 4 times, we put UV relays on the controls with contacts to open the starters. Have not lost a coil since then. This was practical for this site may not be the best approach for all applications.

 

[beanland]

DC Hold-In

DC Hold-In

There are "hold in" devices designed to hold up the voltage at AC coils so they do not drop out. The ones I remember converted AC to DC and charged a capacitor. I assume the coils have to be changes to DC coils.

A constant-voltage ferroresonant transformer could also be used to hold control voltages up if a common 480V control bus is being utilized.