Research at Tunisian Utility Looks to Influence Future IEC Guidelines for Insulators in 
In its May-June 1998 Issue, INMR wrote about the extensive efforts being undertaken by the Société Tunisienne de l’Electricité et du Gaz (STEG) to deal with insulator pollution problems on distribution lines in Tunisia.
As discussed in Part 1 of this article, Tunisia has an unusually aggressive pollution environment stemming from its special combination of coastal and desert exposure. Much of the country is surrounded by the Mediterranean and strong winds from the sea carry marine pollution inland. The country also borders the huge Sahara and sand particles are blown about continuously by the desert winds. Adding to this problem are numerous salt lakes in the interior which spread conductive particles over the surrounding desert when the lakes dry out in the springtime.
Raouf Znaidi has worked for the past decade and a half with the Research Department of STEG’s Distribution Division. During this period, he has studied and reported on the performance of different types of insulators on the 33 kV overhead distribution network in Tunisia. Most recently, in an effort to validate past findings and to develop practical insulator selection criteria for the country, STEG has embarked on a three-year cooperation program with the Swedish Transmission Research Institute (STRI).
According to Znaidi. aside from these principal objectives another important goal of this work is to contribute toward changing IEC methodology for selecting insulators under conditions of maritime and desert pollution. Says Znaidi “the global aim is to finalize our past work in this area so as to meet STEG needs. But, we also want to develop completely realistic laboratory testing to contribute towards IEC standard recommendations for these types of pollution conditions.”
Experience in Zarzis District Provides Example of Pollution’s Impact
STEG’s network is divided into about 30 Districts throughout the country and the performance of each is evaluated based on a range of criteria including number of service interruptions. Every District records and maintains a similar statistical database which then permits comparison of operations to be made across the different Districts. “We have installed software programs for analysis of interruptions to the network” states Znaidi, “and with these we can generate information on their financial impact as well. Service interruptions, however, frequently depend on many external variables which cannot be so easily controlled.” The experience of one STEG District situated around the southern seaside city of Zarzis provides a good example of the impact of pollution on the performance and maintenance requirements of Tunisia’s medium-voltage (MV) network. In many respects Zarzis is an ‘island’ in a large expanse of desert. In addition to heavy coastal pollution, the peninsula on which it lies is also exposed to wind-blown conductive sand particles coming off from the surrounding desert and salt lakes.
