Stability of the gas filled surge arresters characteristics under service conditions

The working point of gaseous filled surge arresters (GFSA) is located near the Paschen curve minimum. It has been proven that the working point of GFSA is more stable when it is located in the vicinity of the Paschen minimum, as in these points the curvature radius is largest and that enables the greatest stability of the working point during exploitation. This paper deals with the influence of external factors (temperatures from -200/spl deg/C to 200/spl deg/C, radiation by high speed neutrons and thermal neutrons in controlled dosage) and working conditions on the stability of commercial GFSA characteristics. Under well controlled laboratory conditions measurements of pulse and DC breakdown voltages were performed for several types of commercial surge arresters. During these measurements, the following parameters were varied: temperature, dosage and energy of the previous neutron radiation, and energy and the number of previous breakdown occurrences on a surge arrester. In accordance to these measurements, a software package was developed to enable the determination of analytical expressions for a suitable pulse characteristics. Statistical treatment of obtained results determined the influence of temperature, previous neutron radiation and previous discharges on the stability of GFSA characteristics. Also, by application of the statistical tests (U-test), the level of irreversible changes in GFSA characteristics under experimental conditions was determined. Obtained results are explained theoretically.