Time to Failure (Continued)
Motor Diagnostics and Quantum Mechanics – Part 17 Conclusion
Howard W Penrose, Ph.D.
ALL-TEST Pro, A Division of BJM Corp
Note: A detailed paper covering this lecture series can be found on ReliabilityWeb: http://www.reliabilityweb.com/art04/mca_concept.htm
We have covered this particular subject as far as we can go within this concept, and without introducing any significant math. The purpose has been to cover the philosophy behind analyzing time to failure using MCA technology. Our next lecture series, starting tomorrow morning, will cover the other half of Motor Diagnostics: Electrical Signature Analysis. This will allow us to include energized testing as part of our estimating time to failure concept, as the dynamic impact of the motor will effect the overall motor ETF.
In the Motor Diagnostics and Quantum Mechanics portion of our overall series, we discussed the difference between classical physics and quantum physics, how it describes the application of MCA, what tests are performed with MCA and how each describe the common insulation failure methods.
The concept of ETF is simple: Present the probability that an insulation system will fail within a stated period of time with a technology that will not accelerate the failure. The tables presented in the Estimating Time to Failure papers, Part 1 and Part 2, were developed based upon the probability distribution following the history of a population of electric motors tested and trended in the field. The probability of failure is calculated simply as: Pa = Na/N where Pa is the probability, Na is the number of failures and N is the number of failures. This can be applied as part of a simple reliability curve e(-t/M) where e is the natural log, t is the time being determined and M is the mean time to failure. This allows us to determine the probability that the insulation system will survive over a specific time period based upon observations from the original evaluated population. This also allows us to assemble an ETF calculator based upon the probability curve, basic reliability algorithms and operating conditions.
Combined, we have been able use ETF to determine insulation failures out to 4,000 + hours.
In the Electrical Signature Analysis series, starting Friday, August 13, 2004 (just because I like Friday the 13th), we will start with definitions covering both MCA and ESA, the properties that make up a full ESA capability and the systems that both have been evaluated on.