![]() It behaves proportionally to changes in voltage and consequently does not show significant sensitivity in the non-linear area of the arrester’s V-I characteristic. The capacitive current represents the current flowing through the arrester’s series capacitance. 3: Peak current characteristic of surge arrester. This qualifies peak current as a reliable indicator of pure capacitive or resistive currents but not for mixed current components. Between these two ranges, peak current is influenced by harmonic distortion due to the growing resistive component and shows low sensitivity to changes in voltage or, more correctly, to changes in the arrester’s V-I characteristic (see Fig. At higher voltage stresses, primarily in a range above U r (rated voltage), peak current orients itself on the peak value of the resistive component. about ![]() The peak value of arrester current is always orientated on the dominant component, i.e. 2: ZnO leakage current (left) and current spectrum (right). 1: Capacitive and resistive current in ZnO surge arrester.Ĭapacitive and resistive currents are superimposed to a total leakage current in which two important values can be determined – peak current and 3 rd harmonic current, e.g. Under AC voltage, this results in two superimposed currents: one is a sinusoidal capacitive current phase shifted -90° to the voltage signal the other is a resistive current that is in phase with the voltage and not sinusoidal but rather shaped as a periodic pulse signal (see Fig. Peak Current, Capacitive Current & Resistive Current: The ‘Agony’ of Choiceĭue to the molecular structure of zinc oxide, MO surge arresters have a complex impedance that consists of a resistive as well as a capacitive component. Side effects and their impact on measurements are also discussed and recommendations given for proper condition assessment of surge arresters. Given this, below is an explanation of the most common examples of leakage current behavior and its relation to various practical operating scenarios. Proper understanding of measured leakage current values, preferably available as periodically logged long-term data, is the best way to allow early recognition of impending failure and therefore to make the decision to replace an arrester. ![]() Humidity ingress and progressive degradation of MOV blocks are the most common reasons for surge arrester failure and ideally need to be detected early on. By contrast, weather and pollution can influence arrester current by adding surface currents and hence introduce possible errors to the values being measured. Temperature and grid related influences such as harmonics in the system voltage play only a minor role since existing methods compensate roughly for these. To build an adequate knowledge base for users of surge arrester monitoring devices, an investigation was conducted of different effects on arrester leakage current that might lead to misunderstanding the data being measured. The information presented is based on first hand experience with a state-of-the-art surge arrester monitoring system that has been evaluated in the laboratory as well as during extensive field tests across countries with different HV systems, climates and environmental conditions. ![]() The goal is to help correct interpretion of measurements and improve decision-making when it comes to arrester maintenance. This edited contribution to INMR by Philipp Raschke of Tridelta Meidensha in Germany offers insight into the different effects on surge arrester leakage current. Utilizing leakage current for surge arrester monitoring can also create confusion since diverse leakage current behavior phenomena must first be understood. However, certain effects on arrester leakage current can lead to measurement errors, incorrect interpretation of data and possibly unnecessary replacement or even sudden breakdown. At present, monitoring leakage current is the prevalent method to verify condition of arresters and more important to estimate their remaining life expectancy. Over the past 30 years, numerous devices with different technologies have been introduced for the purpose of assessing the condition of surge arresters in service. ![]()
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