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Surge arresters, also known as arrester, are often ordered in medium voltage transformers and reactors. They are usually connected between the winding and grounded line terminals. They provide a degree of protection for high voltage surge protection. They can be used for winding voltage ratings of 2.4 kV and above. The arrester should not be confused with a surge protection device (SPD) formerly known as a transient voltage surge suppressor (TVSS), which is suitable for rated voltages of 1000V or less not covered here. This article is intended to familiarize readers with arrester applications and accessories.

Modern surge arresters use metal oxide discs, composed mainly of zinc oxide.  These discs are enclosed in a polymer or porcelain housing with terminals and mounting provisions.  One end is connected to the winding line terminal and the other end is connected to ground.

Most metal oxide arresters are gapless.  In these, the full system line to ground voltage is applied to the metal oxide discs.  Some metal oxide arresters have a spark gap in series with the metal oxide discs.  In the gapped arresters, the system line to ground voltage is taken by the spark gaps.

At normal operating voltage, the resistance of the metal oxide plate is sufficiently high so that the leakage current is several milliamps. When the voltage surge arresters reaches the arrester, the resistance decreases, allowing the surge to conduct to the ground. When the voltage returns to the normal operating voltage, the resistance rises again to limit the leakage current. In a seamless arrester, the transition is seamless. In the arrester, before the arrester discharge, the voltage needs to reach the spark gap of the spark overvoltage.

Article from:

http://www.hammondpowersolutions.com/