Disconnect Switch Induced Transients and Trapped Charge in Gas-Insulated Substations

Field tests have been carried out which permitted direct measurement of disconnect switch operation induced transients in an operating 500 kV substation. These measurements indicate that transients do not exceed 2 pu at the point of measurement and that the trapped charge left on the load side is less than 0.3 pu. Further study of the way in which disconnect switches operate indicates that the trapped charge left during disconnect switch opening depends on the detailed design of the switch.