Thermal fatigue of electrical components.
Thermal fatigue of electrical components.
(OP)
I am currently working on an RCFA of an electrical cabinet that is having premature component failure due to thermal fatigue. I have heard in several training courses that an increase of 10 degrees C will result in a decrease in electrial component life by 50%. However, I am having problems locating a reference that I can use to support my investigation. If anyone knows of a online reference I can use, it would be of great help.
MWMonty
MWMonty
RE: Thermal fatigue of electrical components.
Most reliability books and references will discuss this in more detail
A search for arrhenius and reliability pulled up:
http://nppp.jpl.nasa.gov/asic/Appendix.7.html
which is discussing integrated circuit reliability, but the concepts are the same for anything with this type of rate model.
TTFN
RE: Thermal fatigue of electrical components.
I don't think it will have anything to do with thermal fatigue. If I'm not mistaken you're probably talking about fatigue of either a fuse element or perhaps a bolted or soldered connection. Either way it's metal, not insulation. The 10C Arhenius rule has nothing to do with it.
Can you tell us more specifically what you are looking at?
RE: Thermal fatigue of electrical components.
Thank You for the link. It is just what I need to support my conclusion.
RE: Thermal fatigue of electrical components.
The system I am working on is an electrical control cabinet for a hot oil system. I am seeing an MTBF of 3 months on components (wire, contactors, and fuses). Most failures have been multi-component and result in extended downtime. We have similiar systems on several other lines, but these lines are not subject to the same temperatures. The cabinet we are having problems with is subject to temperatures in excess of 60 degrees C for about 4 months a year. During the cooler months it drops to 40 degrees.
RE: Thermal fatigue of electrical components.
To repeat there are at least 2 different temperature-related aging mechanisms
#1- thermal aging of insulation (unrelated to fatigue) which doulbes by the 10C rule and depends on time at temperature (but not cycles)
#2 - Fatigue type failures of metal components exposed to temperature cycles which impose changing mechanical loading.
RE: Thermal fatigue of electrical components.
The actual temperature of the electrical components could be substantially higher than the ambient, which would certainly degrade their reliability.
TTFN
RE: Thermal fatigue of electrical components.
60C is the ambient temperature. Using thermography, I have found components with a Delta T of 55C. My recommendations to prevent reoccurance is to cool the cabinets using chilled air from our comfort and cooling (this system does not have a heating system.) I am convienced of the failure mechinism. Management is just wanting solid science (i.e. someone from outside the plant) to justify my findings.
RE: Thermal fatigue of electrical components.
RE: Thermal fatigue of electrical components.
"The aging of insulation is a chemical process which occurs more rapidly at higher temperatures according to the Arrhenius reaction-rate theory, as expressed in Eq. (10-63),
h = e^[K1 + K2/(C+273)] where C = degrees C temperature of insulation, K1, K2 = constants determined by test, and h = hours of life."
Hope this helps.
RE: Thermal fatigue of electrical components.
I didn't notice the first time that it appears mwmonty is happy with the link from irstuff.
I'll see if I can remove my post from the power forum.
RE: Thermal fatigue of electrical components.
With the editing limitations However, I will take the risk to luck foolish with the following simplistic explanation:
a- Assuming that the component l follow the Arrhenius life expectancy:
Log[E(t)] = A + B/Tabs
Tabs = Ths+273
Where:
E = Life expended in during time interval t
Ths = Temp hot spot (oC) = Ambient Temp + Hottest- spot winding temp.
t = Time in hours
Tabs = Absolute temp (oK)
A, B = Constant for life expectancy curve of each insulation as follow:
Max Hottest Constant
Spot Temp A B
150 oC -8.270 5,581
185oC -7.941 5,907
220oC -10.453 7,582
b- Using a graph (or equations) for the Percent Relative Life Expectancy (P) versus the Insulation hottest-spot temperature (Ths) the following data are determine
P is defined as follow
P = (E/Er).100
Where: See E defined above, Er = Life expended when operated at rated conditions.
For Example, let’s use Fig 3 ANSI/IEEE C57.96-1989 for Dry Type transformers.
Insulation Hottest Relative Life Expectancy (Approx)
Spot Temp (oC) T@ P=100% T@ P=50% DELTA
150 oC 140 150 10oC
185oC 178 188 10oC
2200C 210 220 10oC
RE: Thermal fatigue of electrical components.
RE: Thermal fatigue of electrical components.
for example, if the activation energy is 1.2 eV, the life reduction is more like 80% for a 10 degree change.
TTFN
RE: Thermal fatigue of electrical components.
Great question! The responses generated are a learning experience! I thought I might have a bit of usefull info for you. In 1990 at IRINFO'90, Mr. Alan C. Pierce of Factory Mutual Research Corporation presented a paper on derating electrical and electrical/mechanical components using tables, a simple equation and temp data. The report can be obtained from Infraspection Institute at www.infraspection.com , contact Jim or Chris Seffrin. The derating info applied to your equipment may assist you in convincing the powers to be of what kind of harm is occuring to their equipment. The Derating information was developed to assist in priortizing maintenace based on thermal excesses to the equipment. The data used to develop component thermal limits for this report is listed and consist of multiple existing standards.
Best of luck, and to those responding to MWMONTY's question, Thanks!
RE: Thermal fatigue of electrical components.
Thanks Again.
RE: Thermal fatigue of electrical components.
http://www.silicavalley.com/archives/Reliability.pdf
http://www.spie.org/web/abstracts/2700/2780.html
http://www.cem.msu.edu/~cem852/lecture_03_25.pdf
etc. for more info
RE: Thermal fatigue of electrical components.
So maybe the biologists or bio-chemists can assist?
Bung
Life is non-linear...
RE: Thermal fatigue of electrical components.
I can appreciate that many reactions rates will double for a fixed change in temperature.
But is the amount of that fixed change in temperature always 10C for any material and reaction? I kind of thought is was different for different materials/reactions,but Bung's discussion makes me wonder.
RE: Thermal fatigue of electrical components.
I made a quick mathcad template applicable to 150, 185 & 220 oC Insulation for dry type transformer and the 55 & 65 oC for oil filled transformer. Although the result do not show exact loss of life of 50 % with 10 oC increment, the values are close enough for practical purposes. That me suspect that the 10 oC rule is applicable to different materials and medium.
An interesting observation of the Arrhenius equation plotted in a log-log scale shows that this relation behaves as a quasi-straight line within a practical temperature ranges.
This characteristic is perhaps the answer of the consistency of the 10 oC rule for any material and insulating media.
RE: Thermal fatigue of electrical components.
There are other failure mechanisms, particularly in semiconductors that hvae activation energies over 1eV up to 1.5 eV, which allows you to test part lifetime using accelerated temperature.
The MIL-STD-883 life test qualification testing uses this principle as the means of certifying that the military IC meets a certin range of reliability and lifetime.
TTFN
RE: Thermal fatigue of electrical components.
This do not appear to have direct relation with the 10 oC rule, but the following statement from a technical source has so much similarity that call my attention: “Each time the moisture is doubled in a transformer, the life of the insulation is cut by one-half”
Since moisture accelerate the degradation of insulation, I suspect that this chemical reaction could be explained by the Arrhenius equation or a similar mathematical model.
Any reference or Internet link in this subject will be highly appreciated.
Thanks.
RE: Thermal fatigue of electrical components.
TTFN