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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum ( )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Posted by: Joseph Murphy ( )
Organization:Research Products
Date posted: Thu Sep 16 12:47:09 US/Eastern 1999
Subject: Transformer Reliability
Hello. I'm interested in finding out if there is any useful information out there regarding reliability estimates for Class II transformers? Specifically, am curious if there any work has been done to characterize the reduction in life as a function of core/windings temperature. Any help or direction appreciated. Thanks. JOE


Subject: Transformer Reliability
Reply Posted by: Bruce Dudley ( )
Organization: Reliability Analysis Center
Date Posted: Wed Sep 22 9:20:29 US/Eastern 1999
The last work on reliability modeling for transformers was done in 1992 for the Rome Laboratory and was reported in the technical report RL-TR-92-197 "Reliability Assessment of Critical Electronic Components". This model for transformers does not have an "end of life" characterization for the wear-out of the winding insulation caused by temperature exposure. The model does have a temperature factor for the failure rate model which is based on the "random" historical failures collected in field operation and extrapolated using an Arrhenius temperature relationship with an activation energy level of 0.11 electron volts. The rate of change with this activation energy is very low, that is, the failure rate varies by a factor of two over the range of 20 to 80 degrees C. In this report, I found life characteristic work was performed for motor winding insulation. The applicability of motor insulation to transformer insulation is an area that would require investigation. For your information the alpha characteristic for general use motor winding is: log(10)^(2357/Tamb+273)-1.83 and the beta characteristic is 1.0.

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