Electrical design analyses studies on ultra high voltage air insulated surge arresters

Abstract

Abstract Air Insulated substations (AIS) experience over-voltages like lightning, switching and temporary over-voltages. The voltage distribution across air insulated surge arrester (AISA) is highly non-uniform and its non-uniformity increases with increase of rated voltage. To achieve non-uniformity voltage factor within permissible limits, special grading shields like window based shields are proposed. In the present study, 420 / 800 kV surge arrester models with composite insulator housing have been considered to analyze voltage distribution across the metal-oxide (MO) blocks. The electrostatic field and voltage distribution analyses are carried out on AISA by considering various shield designs using numerical techniques. Instead of single grading shield, multiple voltage grading-cum-electric field controlled shields are adopted to achieve uniform electric field and optimized non-uniformity voltage factors in the order of ±8 % irrespective of rated voltage of surge arrester. An electrical model is also developed using PSPICE software to calculate voltage distribution across MO blocks. The validity of the network model developed through PSPICE is validated by comparing with the results obtained from numerical analysis. Different configurations of grading shields are proposed and effect of various parameters like rated voltage i.e. 420/800 kV, height of shield, diameter of shield and type of shield like high voltage, floating, LT shield etc. on non-uniformity voltage factor and electric field distribution of surge arrester are analyzed.