Voltage And Current Sensors For A 1200 kV Gas Insulated Bus

New instrumentation being developed for a 1200 kV gas bus system is described. The novel line current and voltage sensors are well-suited to the geometry of gas-insulated coaxial lines. Line current is measured by a toroidal inductor, or Rogowski coil, which is positioned circumferentially around the center conductor at the inner surface of the enlarged outer sheath. The line voltage, sensor is derived from the coaxial configuration of the bus. A 1.5 m long, cylindrical section of the sheath is electrically isolated to form a 100 pF coaxial capacitor relative to the center conductor. This high voltage coaxial capacitor, together with a low voltage capacitor incorporated within the solid state signal processing amplifier, forms the voltage divider. Test results to date indicate the system will meet the requirements for both revenue metering, 0.3% class, and for protective relaying. Outputs of the signal amplifier channels are typically 3 to 5 V rms at normal line power and are suitable for driving static relays and other low load burden devices. While the present work is directed toward an application for 1200 kV, the instrumentation is equally well-suited to lower voltages where more GIS (gas-insulated systems) equipment is in use today.