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About a half of birds migrating from Europe to Africa cross over the temtory of Israel and many of them stay in Israel for wintering.The paper presents the analysis of the high number of transient failures recorded on a high voltage 0 overhead transmission line which leads to the conclusion that in the most cases the cause was bird drops(excretions).

The problems of insulators choice and maintenance in subtropical areas have many complex and specific features. Basic directions of investigations and solutionsto some of the problems that Israel Electric Corp. faced in its network are presented.Most of the results presented in the paper are based on field investigations and service experience rather than on pure laboratory investigations. IntroductionThe rate of transient failures and outages durations on the Israel High voltage (HV) and Extra-High voltage (EHV) overhead transmission lines because of polluted insulator flashovers is much higher than in Europe, USA or Japan. The main cause for this is the specific climatic conditions in the area: 7 -8 months dry period in a year (without rains) followed by4-5 months rainy period in winter (in average -50 rainy days). Often the pollution layer accumulated during the dry period of one year is not washed down by the winter rains and it built-up for several years. The dew that falls out on the insulators for more than 100 nights in a year in many areas of Israel humidifies the pollution layer, makes it conductive and, as a consequence, the probability of flashovers increases. In order to solve these problems we promote the use of insulators w i t h profiles that are cleaned efficiently by the wind (aerodynamic ones ) and have been made of materials that are less affected by the high air humidity and dew ( composite hydrophobic materials).Our company seeks to decrease the failure rate and outages duration in electrical network to European level. This aim compels us to carry out a comprehensive research program to decrease the number of failures caused by polluted insulator flashovers.In the same time our laboratory is active in searching for solutions to reduce the amount of maintenance activity without impairing the network reliability. Investigations of polluted insulators from the network Field investigations and preventive maintenancePeriodical inspection tours along overhead transmission lines have been canied-out in the following main cases : Investigations of transient failures and outages causes. 2.Gathering field experience about new types of insulators (e.g. partial arcs on the surface of composite insulators or coiona sources on their armatures and fittings). 3. Investigations of ionization activity on the insulators surface to estimate the pollution level and risk of flashover and washing neccessity or even replacement of insulators.The electric fields on the surface of HV & EHV overhead line conductors is relatively low in Israel as in many other developed countries. Therefore corona sources on the fittings, armatures and, arc horns and partial discharges along the insulator surface have a major share in the total level of radio interference (RI) and acoustic noise (AN) near overhead transmission lines in Israel. This statement is hlly supported by findings in the 0-7803-3330-6196/$5.00 1996-IEEE 491.