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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This paper presents post event analyses of three inrush events that caused relay misoperation. It then presents the results of an EMTP study that illustrates the degree to which different techniques can mitigate the transformer inrush transient and compares this to the predicted performance of closing resistors in an identical application. It demonstrates that controlled switching of a transformer adequately mitigates inrush transients.

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For new installations of 500-kV gas insulated switchgear (GIS) at the Pin Hook, TN USA 500-kV Substation and the Maury, TN USA 500-kV Substation, the Tennessee Valley Authority (TVA) chose to install an advanced SF 6 gas monitoring system (GMS). This paper will discuss specifics of the GMS and how its use simplifies identification of leaking sections, facilitates planned outages for repair or replacement, and ultimately increases the availability and reliability of the equipment.