Abstract: Liquid, particularly leaked oil or other hydrophobic liquid, is detected by a sensor. This preferably has a hydrophobic membrane (G) that takes up the oil selectively, a radiation source (A) that beams radiation at an interface between the membrane (G) and a window (F), and a radiation detector (H) that receives radiation resulting from interaction (such as reflection, scattering or fluorescence) of the input radiation with the liquid-containing membrane (G). The detector may employ a spectrofluorimeter (H) whose output can be used to characterise the liquid.

Abstract: A changeover switch for a tap changer including a pair of load switches. A diverter switch allows load to be diverted along a second path when its associated main switch is opened or closed. An auxiliary circuit has an auxiliary switch and a varistor connected in parallel across the secondary of a transformer. When the auxiliary switch is opened the varistor impedance is reflected onto the primary of the transformer which causes the current in the main switch to divert through the diverter switch so that the main switch can be opened or closed with substantially no load on it.

Abstract: Apparatus for determining the volume of gas dissolved or entrapped in transformer cooling oil includes an oil receiver, a metering space and a piston pump arranged to apply a reduced pressure to oil in the receiver and to transfer the gas which is liberated from the oil into the metering space. The piston pump is connected to and controlled by a controller. The metering space comprises a cylinder which accommodates a piston which is connected to be moved by an actuator which is connected to and controlled by the controller. The pressure detector is provided which is responsive to the pressure in the metering space and is arranged to deliver a signal indicative of the magnitude of the pressure to the controller. A transducer is connected to the controller and is arranged to produce a signal, when the said pressure reaches a predetermined value, which is indicative of the volume of gas within the metering space.