Purpose-built test rig for gas insulation breakdown tests under lightning impulse

A new test rig has been developed specifically for gas research work, which includes a pressure chamber, control measures, and a recovery system of the gas. The air-tight pressure chamber was designed and tested to withstand pressures of up to 5 bar (abs). Through help from a reliable sealing gland, wires were passed through the pressurized gas inside the vessel to the outside to provide a means of controlling the gap length of the electrodes, without the need of removing the gas. Other control measures include humidity, temperature, and pressure readings. The humidity and temperature are read wirelessly and from the readings, the necessary atmospheric corrections can be made according to standards. Safety measures are equally important and were achieved by using a pressure relief valve. The valve is set to release the gas at 6 bar. A recovery system of the gas mixture was used so that after each test, the gas was properly stored in cylinder bottles and not being released into the atmosphere. As it is important to study the `deteriorated' gas for future works, this recovery process provided a means of obtaining the deteriorated gas to be investigated. From initial tests on air breakdown, it was found that U50 increases with pressure. Rod-plane configuration provides lowest U50 values due to its electrode geometry, followed by R12-plane and plane-plane configurations.