Surge arresters for medium voltage and high voltage systems
IEC line discharge, class 1- 4
Polymeric and porcelain constructions
Voltages 3KV – 132KV
Surge arresters are widely used in distribution and transmission networks to ensure the protection of assets against overvoltages resulting from switching in the network or from lightning strikes on the line.
Surge arresters are often a sacrificial device which protects the considerably more expensive transformers or reclosers, in addition to substation assets.
The higher the Line Discharge Class of the arrester, the higher it's energy capability. This means that a high-class arrester would have lower residual voltages in the event of a lightning strike, and would be capable of enduring a higher energy lightning strike. Of course, the cost of a higher class arrester is much higher.
Arresters are always installed close to the device they are protecting, connected with a lead which is as short as possible. Arresters are mounted on pole top transformers, usually on the tank with a cable connection to the bushing. In distribution networks up to 33KV the most common arresters are IEC Line Discharge Class 1 arresters, also commonly known as distribution arresters, due to their low-cost position. A significant number of them are used on distribution transformers in order to keep down costs. The lower energy, lower class arrester is often a sacrificial device, destroyed whilst protecting the asset in the event of a lightning strike. In such an event, the arrester must be replaced.
All arresters currently use Zinc Oxide blocks in their construction and as the active element of the arrester. Today's arresters are gapless, meaning that there is no air gap within the construction. This is made possible by the unique property of ZnO, which has extremely high resistance at zero voltage. With higher voltages the ZnO drastically drops its resistance, allowing current to flow through it.
There are many different types of arresters ranging from AC or DC, for use in railway networks, generators, etc, and may differ greatly in construction, voltage range, mechanical properties, etc. Each design is adapted to its particular application.