Estimates of the world market for surge arresters from 1 kV to 43 kV vary from US$ 250 to 350 million. As with insulators, there is a fairly high degree of concentration in this industry, with the leading global brands together holding more than half the market and possibly as much as two-thirds. The remainder is shared among a large number of speciality manufacturers that serve mostly regional markets, some of whom have operated with technical assistance from the major players. This is a fairly stable business and distribution arresters are often viewed as a commodity where technology has reached a point where there are few failures due to poor materials, design or quality control. This is supported by the fact that price plays a central role in the purchase decision.
The market for distribution arresters has two segments: power supply companies are the larger part and these are often served by myriad distributors who are aligned with major manufacturers. Another segment is accounted for by electrical apparatus manufacturers (OEMs) producing distribution transformers, switches and switchgear. Most applications of distribution arresters are focused on protecting equipment rather than overhead lines. The OEM market has a somewhat different perspective than utilities when it comes to purchasing arresters. Here, issues of performance and after-sales service take on greater significance. Most important is delivery as well as the flexibility to meet orders in a timely fashion. While price is always an issue, OEM customers also look for technical support in the way of competence in the application as well as in insulation coordination.
Technology Development
There have been two fundamental shifts in technology for distribution arresters over the past 30-40 years years. One has seen substitution of metal oxide varistors in place of the silicon carbide gap-type designs dating from the 1950s. The second has consisted of virtually total replacement of porcelain by polymeric materials as the external housing. Together, these changes have completely transformed the appearance and performance of modern day arresters at distribution voltages.
Polymeric Housing Materials
Once the transition from porcelain to polymeric housings for distribution arresters had become complete, the topic of interest became the relative performance of alternative polymers. Basically, major categories of polymeric materials used as housings for distribution arresters include: silicone rubber, ethylene propylene diene monomer (EPDM) and ethylene vinyl acetate (EVA). Data on which material dominates sales are difficult to obtain, however silicone rubber is likely the housing found on the majority of distribution arresters. While the relative performance of these polymeric housing alternatives is still debated, most feel that silicone rubber has ideal properties that justify its use in spite of a higher cost. For example, silicone has a higher bonding energy than EPDM making it less vulnerable to being broken down by UV radiation and ozone. Moreover, due to long-term hydrophobic properties, it performs better under conditions of high contamination.
Design Features
The failure of a polymeric arrester is rare, estimated at less than one failed unit per 1000 per year. However, since millions of such arresters are in service, that still means a high number will fail each year. The most important variable determining failure rate is level of isokeraunic activity in the region where the arrester is installed. In this respect, the arrester will have operated and absorbed an overvoltage from a direct strike and failure (or sacrifice) of the arrester is not related to quality. However, other factors that are controllable also influence failure and, more significantly, failure mode. Typically, these relate to arrester design and construction.
Role of Disconnector
Most distribution arresters sold today – especially those in the Americas – are equipped with a disconnector device that separates the ground lead to ensure that arrester failure does not necessarily cause a permanent outage. Also, there is visible indication for maintenance staff of the need to replace the arrester. Not all utilities throughout the world want this feature, however, some preferring to have the line taken temporarily out of service in the event of arrester failure due to factors such as a direct lightning strike. This is the case in a number of European countries.
The disconnector on a distribution arrester is specialized and should not be regarded as a standard accessory. Rather, its design must incorporate features to meet the operating requirements of utilities, which emphasize not only lower numbers of interruptions but also interruptions of shorter duration. The disconnector unit must be strong enough to withstand normal surges yet operate quickly whenever these are of a magnitude that overwhelms the arrester. Indeed, disconnectors are a point of differentiation between various suppliers and a key design element of a distribution arrester. For example, some power utilities have looked to change their arrester supplier solely because they were dissatisfied with the slow operation (i.e. less than optimal time/current curve) of the disconnectors that were part of the units purchased. As a result, overvoltage situations that resulted in arrester failure often triggered operation of breakers – a situation they did not want. One of the past concerns of the arrester industry related to the fact that disconnectors operate on the basis of a temperature-triggered tiny explosive charge and can present difficulties in being shipped using normal channels.
Alternative Manufacturing Processes
Apart from different philosophies for containment of the metal oxide blocks, the second major construction variable in a distribution arrester is how the polymeric housing is applied to the bound internal varistor column during final production. Two principal types of production technologies have emerged. The more widely utilized could be referred to as the slip over technique since it sees a pre-manufactured hollow cylindrical polymeric housing pulled or stretched over the contained blocks. The second method could be called the direct mold technique since here the housing is molded directly over the column under some combination of pressure and temperature. These two manufacturing technologies play a fundamental role in many variables since they influence relative production costs, consistency of quality and production lead timesFuture Expectations
There is a consensus that distribution arrester technology is mature and that the basic design of these arresters has reached the state-of-the-art in terms of cost-effective manufacturing and high quality of materials. Although this technology has been employed since the mid 1980s, there do not appear any breakthroughs in displacing basic components such as zinc oxide blocks or polymeric housings. Rather, the emphasis by suppliers will remain focused on issues such as more automated manufacturing and testing for high volume production and also refining processes for reduced cost, higher yield and better reproducibility. Suppliers that succeed in this field will be those that have mastered the process and control all the costs. This may involve looking into material formulations to identify opportunities for faster curing and reducing cycle times. Also, developing a more flexible manufacturing process will enable major global suppliers to offer a single platform technology that, while using the same basic components, can modify design to meet special user needs.
One area where industry observers see opportunity for product development is enhancing performance of metal oxide blocks, e.g. developing greater energy absorption capability in an existing volume of metal oxide varistors. Another goal of product development might consist of better matching arrester function to the special requirements of each application. A logical final step might even be transfering the voltage limiting property of the arrester to equipment itself. For example, rather than being located outside, the varistor elements could somehow be placed inside the transformer or within its internal insulation to allow for discharge in case of overvoltage. In this manner, the insulation itself would take on voltage limiting properties. But there would be a need to solve certain technical issues such as how the excess energy would be dissipated and new materials would have to be designed to absorb this excess energy.
Looking back on what has been achieved in the area of distribution arresters, silicon carbide gap designs were around for a long time. Given the fact that discovery of the metal oxide technology that ultimately replaced was a serendipitious event, replacing this technology in the future may well require another such ‘accident’.
From：https://www.inmr.com/development-distribution-arrester-technology/
