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Carbon Formation at Contactor Point

05/18/2017 10:04 AM

Hi,

I need to know like whats the reason for carbon deposition on contactor points(not coil point). I think of loose connection of lugs to that contact point due to which low pressure at the contacts leading to arc formation and hence the carbon gets deposited.Am I right...? If not kindly let me know the reasons behind this..

regardsm

ram

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#1

Re: Carbon formation at contactor point

05/18/2017 10:31 AM
  • A second possibility is that the release spring has become bent, damaged or weakened in some way.
  • A third possibility is that the contactor is being operated above the manufacturer's rated values.
  • A fourth possibility is that there is mechanical damage somewhere and the plunger isn't "going all the way".
  • A fifth possibility is that some organic material has gained access to it and has become carbonised with either the closing arc or the release arc.

In any case, it cannot be seen from here.

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#2

Re: Carbon Formation at Contactor Point

05/18/2017 12:16 PM

Run a small reverse current across the contact points to eliminate the C build up.

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#9
In reply to #2

Re: Carbon Formation at Contactor Point

05/18/2017 4:47 PM

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#3

Re: Carbon Formation at Contactor Point

05/18/2017 12:51 PM

"... and hence the carbon gets deposited..."

.

.and in that scenario (as well as the second third and fourth provided by PWSlack), from where do you imagine the carbon deposited arrived? Atmospheric CO2?

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#4

Re: Carbon Formation at Contactor Point

05/18/2017 1:48 PM

How do you know it's carbon and not some black, metal oxide?

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#5

Re: Carbon Formation at Contactor Point

05/18/2017 1:53 PM

Is it really carbon or oxides of copper?

If it's carbon, it might be breakdown products from a plastic housing from the heat of the arc. (I can remember, long ago, having carbon arc paths in a plastic automobile distributor cover.)

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#6

Re: Carbon Formation at Contactor Point

05/18/2017 3:44 PM

You cannot tell by looking if carbon track or oxidized metal from corona or arc.

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#7

Re: Carbon Formation at Contactor Point

05/18/2017 3:46 PM

Here is a nice, old article on the chemistry of carbon build up from arcing contacts.

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#12
In reply to #7

Re: Carbon Formation at Contactor Point

05/19/2017 12:26 AM

That link is awesome Redfred! GA from me.

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#13
In reply to #7

Re: Carbon Formation at Contactor Point

05/19/2017 8:45 AM

I noticed in that article that (1) the brown deposits are polymeric in nature, and (2) there is considerable aldehyde and ketone infrared band characteristic, (3) soluble only in strong primary amine or pyridine.

I wonder if we have something "novel" here (besides for it being a nuisance in highly utilized switchgear)?

Could we be looking at a distance cousin in of graphene oxide (with perhaps quinone-like structures). No mention of redox characteristics of the brown polymer.

What if the stuff on the palladium contacts is the world's best catalyst for splitting water? Wouldn't that be interesting...It appears the new catalysts (that might lead to cheaper fuel cells, for example) are in fact GPO structure (with high proton permeability, very good redox catalysis of hydrogen (from water), and have found application (as I recall) in a new isotope enrichment scheme for heavy hydrogen isotopes owing to the factor of up to 10 transport number of protium over deuterium.

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#15
In reply to #13

Re: Carbon Formation at Contactor Point

05/19/2017 9:00 AM

I was casually wondering if graphene formation was happening, too.

My point for the OP is that the formation of carbon on contacts on a "simple" switch is a much more complicated process than many would think. It involves chemistry, kinematics, solid state structure theory, electrical engineering and all of these over a wide range of temperatures as arcs form and quench.

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#16
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Re: Carbon Formation at Contactor Point

05/19/2017 10:09 AM

...and has not much to do with contacts involving palladium actually opening. It even forms on palladium contacts when there is just sliding motion with friction.

Note that silver does not apparently catalyze this, and silver plated copper buses are what is typically used in HV switchgear.

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#21
In reply to #13

Re: Carbon Formation at Contactor Point

05/20/2017 2:24 AM

I think you should send this to Sir Martin Poliakoff of Nottingham University. He might have an answer to your speculation or know who might be interested.

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#8

Re: Carbon Formation at Contactor Point

05/18/2017 4:46 PM

Another possibility is this has happened:

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#10

Re: Carbon Formation at Contactor Point

05/18/2017 8:07 PM

It's always enlighting when the OP checks out and never returns. And everyone was civil to him/her this time

"loose connection of lugs" usually results in burnt insulation on the incoming/ outgoing wires along with other problems resulting from loose connections. Loose connections will produce carbon and

Nice article redfred, thanks for sharing it

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#18
In reply to #10

Re: Carbon Formation at Contactor Point

05/20/2017 2:00 AM

You're right. But those conversations are still good for everybody and maybe the OP read what they needed to to answer their question.

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#19
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Re: Carbon Formation at Contactor Point

05/20/2017 2:04 AM

Speaking of civility, where is Lyn? I miss that crotchety old fart! He googled-linked hard, right on the question and ferreted out quite a few students with test questions!

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#11

Re: Carbon Formation at Contactor Point

05/18/2017 9:51 PM

Yes, very interesting read on that article, thanks for that. Although there will be a big difference in issues relating to something as small and lightly loaded as a telecom relay vs a line voltage contactor for an induction motor, the article raises a commonality that I'm sure exists, that of airborne contaminants that are volatilized in the process and deposit themselves in the arc path.

I ran into this issue while working for Siemens and was assigned to investigate failures of low energy auxiliary contacts in large power contactors used for elevator controls. The big contactors were switching the traction motors and/or hydraulic pumps, but the side-mounted aux contacts of those contactors were being used on TTL level signals for the elevator control computer system. The aux contacts would become intermittent after about 6 months of use, failing to provide the proper feedback signals to the elevator controller, forcing a safety shutdown. That, as you might imagine, was problematic for the elevator vendors. Serious resources were poured into this investigation because the elevator industry was a $10+ million annual business for Siemens, not something they wanted to lose. To make a long story short, the contacts were getting a film built up on them, similar to what is described in that article, and it too was organic compounds. The film would build up until it eventually became an insulator for the low energy (0.7mA 5VDC) TTL signals. These were not hermetically sealed relays, but they were enclosed, plus they were gold flashed and bifurcated (twin paths). The bigger mystery was the source, which turned out to be the main contacts. Airborne oil from the elevator operation was getting into the main contact arc chambers, then vaporized by the arcing. On the main contacts themselves, there was a wiping action in their design that kept them somewhat clear, but the organic compounds from that oil combined with the ozone from the arcing and form and coating everything inside, including the contact surfaces. Then because there was insufficient arcing of those low energy circuits to burn it off again, it just built up until it created a dielectric. This by the way took over a year of investigation to find.

Bottom line from all this happy BS; there are PLENTY of available sources of potential carbon compounds that can build up on contactor contacts, you don't need to look farther than whatever the machine is doing. MOST higher quality contactors are designed such that the main contacts will slide against each other when they close, even very slightly, to help keep it from building up; an action referred to as "wiping". The organic compound debris may build up around the edges, but that is generally inconsequential. If it is building up to the point of becoming a dielectric, you have a very poorly designed contactor, likely selected on price, not quality.

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#14
In reply to #11

Re: Carbon Formation at Contactor Point

05/19/2017 8:46 AM

What got me was that the deposits still formed under sliding contact conditions.

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#20
In reply to #11

Re: Carbon Formation at Contactor Point

05/20/2017 2:17 AM

Reading your story and thinking about the Bell Labs article I can't help but wonder if the source in these failures is due to out-gassing of hydrocarbons from plastics in the construction of the relay. I would bet, after reading the Bell Labs study, that if the relay was covered and used ceramics instead of plastics, then the low power contact film would not readily form. It might take years instead of months because the source of carbon would be CO2 from ambient atmosphere only and not nearby plastic sources of longer chain molecules.

Just Sayin'.

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#22
In reply to #20

Re: Carbon Formation at Contactor Point

05/22/2017 10:05 AM

I was guessing along those same lines. Not sure how much potential in volts is required to break up CO2 in air back all the way to carbon, interesting experiment, though.

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#17

Re: Carbon Formation at Contactor Point

05/19/2017 10:49 AM

Arc formation can be caused by a lot of things besides loose connections. Imagine an ignition coil on a car. when the points open, not only does the collapsing magnetic field induce a high voltage in the secondary, it also produces a similar "less high voltage" in the primary. Without the condenser (capacitor), the points would also arc along with the spark plug. A similar phenomenon occurs with the sudden decay of current thru other xformers/windings/heat-coils/etc (AC or DC). A lot of times each individual load has its own "noise filter" which also limits that voltage spike when it's shut off. But then again, a lot times there is none. And so some kind of voltage-spike suppressor needs to be used with the breaker(s)/contactor(s) to prevent arcing during the opening of it/them.

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#23
In reply to #17

Re: Carbon Formation at Contactor Point

05/22/2017 10:08 AM

Yes, one has to watch it when using any sort of coils in conjunction with an Arduino circuit (they absolutely cannot tolerate any negative going potential at the terminals).

Using best to clip those coils, or DC solenoid valves with an RC in series on the upstream lead to coil, and back side, connected bridge across coil ground. That works. Diodes also work, if you don't blow them out.

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