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 Post subject: Failure mode of lack of lubrication
PostPosted: Wed Mar 07, 2012 5:08 pm 
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I've found plenty of data out there discussing equipment failures from lack of lubrication when it is equipment that should normally be operating and gets into corrosion/abrasion issues.

Circuit breakers however are a bit of a different animal because most of them spend most of their operating life sitting with no activity except hopefully for occasional exercising.

Does anyone know of any data sources referring to this condition...lack of lubrication leading to failures such as "seizing up"? Reason being that using IEEE 493 data I can reasonably model failures such as a trip unit that does not work right (does not trip or out of calibration) but the more interesting mechanism and the one that these days is far more common is failure of the mechanical linkages.

On the same subject, is there any available data out there indicating what the reliability of the newer magnetic actuators is over the traditional linkage systems?

Similarly, the old IEEE 493 data paints vacuum contactors in a very, very ugly light because of the failure rates of the early versions. These days it is well recognized that they are so reliable that they are preferred over other systems. However the only data I found was a tech note in Powell's library that said they had 20K units in service over 6 years without a single failure. It seems like it should be substantial but data would be really helpful. Is there any more up to date reliability data on vacuum breakers? Or SF6 for that matter that IEEE 493 doesn't even have data for?


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PostPosted: Thu Mar 08, 2012 8:02 am 
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CSA Z462-12 Annex B is titled "Safety-related electrical maintenance" (no equivalent in NFPA 70E-2012). In Clause B.1 - General, it goes on to say:
Quote:
Studies by the Electrical Safety Authority of Ontario indicate that 66% of safety incidents can be attributed to maintenance-related issues. A survey performed by the InterNational Electrical Testing Association (NETA) in October 2007 indicated that 22% of service-aged circuit breakers had some type of malfunction and 10.5% did not operate at all during maintenance testing.

I've tried to get that survey to see the whole data, but nothing so far.


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PostPosted: Thu Mar 08, 2012 10:05 am 
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According to CIGRE, about 80 percent of major and minor circuit breaker failures are of a mechanical nature. About 50 percent of these mechanical problems are in the mechanisms. Lubrication issues have been identified as a major contributor to mechanism problems.

I don't think there is much data available on magnetic breakers due to small sample size.

Regarding vacuum bottles, failure rates are increasing dramatically due to age. Design life is typically 20-30 years and VCB's started to become common in the 80's, so we are living on borrowed time in many cases. Until recently there was no way to predict remaining life on vacuum bottles in the field, the traditional tests were a go-no-go hipot test and contact erosion measurement.


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PostPosted: Fri Mar 09, 2012 4:42 am 
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According to CIGRE, about 80 percent of major and minor circuit breaker failures are of a mechanical nature. About 50 percent of these mechanical problems are in the mechanisms. Lubrication issues have been identified as a major contributor to mechanism problems.

I think I found the CIGRE report once. The only major fallacy in the one I saw is that it is specifically related to HV/EHV breakers (above 35 kV for the most part). Unfortunately in an industrial setting even if most of your equipment is on the "high" end of that scale, it doesn't do much good. If however I was looking at utility transmission lines, the CIGRE data I saw was very relevant. I am aware also that ABB quoted it in one of their recent technical articles but it was not attributed to anyone.

I don't think there is much data available on magnetic breakers due to small sample size.

The best way to deal with the "no data" scenario when you develop a new mechanism is that there is a large body of modelling data that goes down to the specific component or mechanism level. That is the methodology that SEL uses for their trip units. And there is a wide body of various safety rated devices (relays, IO modules, sensors such as pressure pads, light curtains, E-Stops, key locks, etc.) on the market now that can't possibly have real failure data for the failure rates they claim (10^-6 or less)...they are modelling these via one of the component-level failure rate data sets. All claim IEC 61508 design specs although that's just an overall performance spec. Most folks are looking for TuV or equivalent markings because manufacturers have been known to cast things in the best light.

Regarding vacuum bottles, failure rates are increasing dramatically due to age. Design life is typically 20-30 years and VCB's started to become common in the 80's, so we are living on borrowed time in many cases. Until recently there was no way to predict remaining life on vacuum bottles in the field, the traditional tests were a go-no-go hipot test and contact erosion measurement.

Agreed. So far what we have though for data for ANY purpose (safety or otherwise) is IEEE 493 and a scattering of data published elsewhere. The inherent problem with this data set is that most of it is very old and probably no longer relevant to a lot of current equipment (most data was collected from the 1970's to 1980's) except to older equipment. It models everything as a random failure. This is entirely accurate for about 80-90% of electrical equipment according to studies done by Nolan et al., and revalidated by EPRI and U.S. Navy. There are a FEW devices however which exhibit trends other than random failures. Unfortunately almost all of them are power electrical devices (contactors, circuit breakers, transformers). There is very little data indicating age-related much less preventative-maintenance related failure modes.

So...I was looking for "component level" data which would provide information about failure rates of mechanisms with lifespan-type data. Otherwise, the failure rates are so low with say circuit breakers that justifying maintenance on a probabilistic safety basis (which most risk assessment codes are based on) is problematic at best because the best I can do is to model it as a random failure in which case periodic testing of a device that rarely fails leads to very long testing intervals.


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PostPosted: Fri Mar 09, 2012 11:28 am 
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There is plenty of data for LV Air breaker failures down to the compoent level from EPRI, each data set is for a sepcific breaker model and only for thos eused in nuclear 1E applications. I just don't have the time to summarize all of that data together. And that data is optomistic due to the fact nuclear plants overhaul thier breakers every 10 years at the longest. The failure rates in an industrial environment would be much worse.


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PostPosted: Sun Mar 18, 2012 6:14 pm 
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PaulEngr, are you looking for LV or MV breaker failure data due to lack of lubrication? The mechanisms and failure modes are totally different between the two. Do you know any engineers at one of the major manufacturers that you could talk to? They tend to have the best data on this, although they usually don't share it on the record.

From what I've heard on LV breakers lack of lubrication is not actually a failure mode. The magnetic forces generated in MCCB, insulated case, and LVPCB are large enough that lubricants that have turned to sludge will not cause a failure to operate, or even a detectable delay in operation.

MV breakers are a much different story and lubrication issues can certainly cause problems because the electromagnetic forces resulting from the fault current do not help to open the breaker - all of the force used to open the breaker is derived from other sources.

The Powell tech brief that you referred to discusses vacuum bottle failures used in circuit breakers, not necessarily vacuum circuit breaker failures. I'm sure there have been numerous vacuum circuit breaker failures, although their record with the bottles may be very good.


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PostPosted: Mon Mar 19, 2012 7:18 am 
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jdsmith wrote:
From what I've heard on LV breakers lack of lubrication is not actually a failure mode. The magnetic forces generated in MCCB, insulated case, and LVPCB are large enough that lubricants that have turned to sludge will not cause a failure to operate, or even a detectable delay in operation.


As far as LVPCB's are concerned I disagree and EPRI has plenty of failure data to back that up. NETA recently released data from all of it's members covering several years and thousands of tests and shows the same results as the EPRI data, lack of or improper lubrication is the most common cause of failure for LVPCP's.


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PostPosted: Mon Sep 17, 2012 2:13 am 

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PaulEngr, is there really nothing that can be done about preventive maintenance of the power electrical devices you mentioned? If these devices exhibit trends other than random failures, can nothing be done?


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