Application Note www.megger.com Insulation resistance testing of surge/lightning arresters Introduction Electric power transmission and distribution systems are vital for modern life. And, since the electricity these systems provide is essential, then these systems are essential too. One of the less celebrated components of these systems is the humble surge arrester. These arresters serve the important job of keeping the electric supply smooth and steady. As such, these devices must be tested regularly as part of a maintenance program. This application note looks at what a surge arrestor is, the test procedures of insulation resistance testers, as well as present test results and recommendations. Figure 1: Lightning strikes are a chief cause of system overvoltage What is a surge arrester? A surge arrester is a key component of electrical transmission and distribution systems. They are commonly found on top of transformers and can change their resistance depending on the voltage applied across them. The applied voltage can rise because of lightning (see Figure 1) or system faults, among others. Arresters have been designed to have a high resistance at normal operating voltages, which can then drop to low resistance once the applied voltage rises above normal (see Figure 2). They can do this by using discs of MOV (Metal Oxide Varistors), like zinc oxide which has the property of changing resistance based on the voltage applied.
Next page: Artikel om överspänningsskydd: Insulation resistance [2 / 5]
