RELIEF DEVICES
Very high pressure is generated following an electrical fault under oil. These pressures could easily burst the steel tank if they are not relieved. An explosion vent was used until the early 1970s. It consists of a large-diameter pipe extending slightly above the conservator tank of the transformer and curved in the direction of the ground. A diaphragm (made of glass usually) is installed at the curved end. It ruptures at a relatively low pressure, releasing any force buildup inside the transformer. Since the early 1970s, a self-resetting pressure relief vent was installed on transformers. When the pressure in the transformer reaches a predetermined level following a fault, it forces the seal open under spring pressure. This relieves the pressure to atmosphere.