WATAK PERLINDUNGAN BLOK ZnO YANG DIGUNAKAN PADA ARESTER 20 KV TERHADAP SAMBARAN ARUS IMPULS BERULANG

The use of a lightning arrester in an electrical power system is very important in giving protection to electrical equipments, such as a power transformer, against transformer damage due to lightning strike, against possible damage due to a lightning arrester,. A lightning strike having high voltage and high current will travel through a transmission or a distribution lines reaching electrical equipment. If the electrical equipment doesnot have any lightning protection, it will be damage due to lightning strike. In a lightning strike condition, an arrester cuts the impulse voltage in a safe voltage value, which is under the protected electrical equipment BIL. The effect is that the electrical equipment will be safe. However, in the condition when the impulse current strike happens repeatedly with high value of current amplitude, the arrester will probably no longer be able to provide protection to the electrical equipment. Therefore, it was developed a research to study the effect of multiple impulse current to an arrester by applying various value of impulse current peaks. However, due to low value of direct voltage that can only be used by a multiple impuls current generator, then it cannot be used to study a 20 kV impulse current arrester. Instead, the study was directed to the application of various impulse current peaks to a ZnO arrester block, which is one of 7 ZnO arrester block ones of the 20 kV arrester. Eventhough this research was conducted to a ZnO arrester block, but the data obtained can be used to analyse the 20 kV ZnO arrester characteristic. The application of 600 A, 1300 A, and 2500 A peak impulse current to a 5000 A ZnO block resulted in the damage of the ZnO block, with in detail explanations as written as follows. The impulse current peak of 0,12 p.u (600 A) resulted in the damage of 28,57 % of ZnO blocks. While the 0,26 p.u impulse current peak of 1300 A resulted in the 50 % damage. One hundred prosentage damage was caused by 0,5 p.u impulse current peak in the order of 2500 A. Eventhough the impulse current peak value was less than the current rating of the lightning arrester, the impulse current was able to make the impulse current arrester damage. This is certainly the result of repetitive impulse current strikes. When an arrester was damage, it produced small value of arrester residual voltage. So, during normal condition, even when there is no impulse strike, the arrester allowes high value of current passing to ground similar with line to ground short circuit current. This makes a circuit breaker opening electrical power supply. When the damage of the arrester is in term of the arrester opening making the electrical equipment protected by the arrester will be damaged due to the existence of impulse current striking the electrical equipment