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TVA identified an increasing failure rate of 132-kV (106-kV Maximum Continuous Operating Voltage) porcelain arresters on the 161-kV system. A cross-organizational team was formed to determine the root cause of the 19 arrester failures and provide solutions. The team researched arrester failure modes and solicited input from arrester experts. A root cause diagram is discussed and multiple failure modes were ruled out. Multiple failed arrester units were dissected indicating moisture ingress as the root cause leading to the recent failures. Computer simulations contrasted faults through the Metal Oxide Varistor (MOV) block stack versus faults flowing through the air cavity surrounding the MOV stack. All 19 failures were recorded by digital fault recorders (DFR). The DFR waveforms were compared to the computer simulations showing that the arresters flashed over the internal air cavity. Based on the available physical evidence, moisture ingress is the likely root cause issue for the failures from 2002 to date.

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