Metal-Oxide Surge Arresters for Gas-Insulated Systems, Phases I and II. Final Report

摘要

The development of metal-oxide surge arresters for gas-insulated systems is described. The arrester is contained in SF sub 6 gas in an aluminum enclosure which is designed to connect directly to a port in a gas-insulated substation. Special MOV blocks were produced for operation in SF sub 6 . A technique was developed for soldering these blocks together for strength and simplicity in assembly. Special care is taken so that the soldered blocks are not affected by high-energy discharges. Three, 362kV prototype arresters were assembled, each using three parallel columns of these soldered 50-mm blocks. The electrical length of each column is 2330 mm. This MOV assembly is centered within a 660 mm (26'') diameter by 3451 mm long aluminum tank. Uniform grading along the MOV column is achieved by a series of ceramic capacitors which are connected along the column. This prototype was designed on the basis of results from three types of analytical studies. First, a heat-transfer model was developed to predict the temperature of the MOV blocks for various operating voltages, currents, and ambient temperatures. A thermal mock-up was assembled to verify this heat-transfer model and provide empirical coefficients. Second, electric-field derivations were carried out to ensure that electric stresses would be kept below 4kV (rms)/mm. Finally, an electric-circuit-equivalent model was prepared to derive the values for the grading capacitors. Continuous testing for 72 h at a-c voltage in the range of 209 to 285kV confirmed the predicted operation and thermal stability of this prototype design. The behavior of this arrester in typical power-systems applications are shown by computer calculations for lightning surges and switching operations. The expected effects of seismic activity and internal fault arcs are also derived. Basic characteristics of gas-insulated metal-oxide arresters for 69, 138, 230 and 500kV were also derived. (ERA citation 08:023438)