metal oxide disks may go through a lengthy term alternation in their characteristics

Because the initial introduction from the MOV arrester, it's been recognized that metal

oxide disksmay go through a lengthy term alternation in their characteristics. This transformation in characteristics is called aging. If the modification in characteristics leads to more losses at normal operating current, it can result in an arrester failure.

Causes: Improper manufacturing from the disk. Failure Mechanism: At normal operating voltages, the losses progressively increase resulting in internal heating. Once the generated heat exceeds ale the arrester to dissipate heat in to the

atmosphere, it can result in dielectric failure along with a fault around the system.

Indicators: Hot arrester at operating temperature, excessive electrical losses at operating current, some disks much different in losses than the others within the

same column of disks, nonlinearity from the disk reduced as proven on Mire trace,

common alternation in many arresters from exactly the same vintage, type and

manufacturer. Cautions: This failure mechanism can look the same as a TOV overload.Less frequent reasons for Arrester Failure and Overload Exterior Contamination: This kind of overload can result in exterior flashover of porcelain housings or excessive internal partial discharge. Improper MCOV or TOV Rating: The

installing of arresters by having an MCOV lower compared to steady condition system current can lead to arrester overload for which would seem like minor TOV. For instance, if the machine has neutral impedance installed, it takes a greater MCOV arrester than the usual grounded neutral, a fault around the system can result in arrester overload around the united nations-faulted phase. Unbalanced Electric Field: This can be a failure mode that may occur with an arrester if the arrester is mounted to shut to some ground plane of some other phase. This missinstallation condition can result in partial discharge within the internal amount of the arrester that can result in failure. This condition might also result in overheating of the disks as a result of current imbalance. This failure can also be caused through improper grading rings around the arrester.

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