The paper presents the results of investigation and engineering analysis by Exponent of the failure of a 220-MVA generator step-up transformer in Southern California. The incident was caused by a dielectric breakdown from the high-side C-phase bushing to the side wall of the transformer. The ensuing fire continued for 27 hrs, fueled by approximately 11,000 gal of dielectric HYTRANS 61 oil. The paper will discuss the investigation conducted as per the IEEE C57.125 “Guide for Failure Investigation, Documentation, and Analysis for Power Transformers and Shunt Reactors,” [1] and the engineering review and analysis to identify the likely failure scenario(s).
This paper is a review of propagating faults in printed circuit boards (PCBs) from the perspective of using the resulting burn and melted copper patterns to identify likely locations of fault initiation. Visual examination and x-ray imaging are the main techniques for examining PCB propagating faults. Once the likely fault initiation location has been identified, fault tree analysis can be used to determine the root cause for fault initiation. The paper discusses the mechanisms by which PCB propagating faults occur. The method of determining the likely area of initiation of the fault using visual examination of the PCB burn pattern, x-ray imaging, and the layout artwork for the PCB is discussed. The paper then goes on to discuss possible root-causes for the initiation of PCB propagating faults and some of their considerations.
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