ALTERNATING VOLTAGE DETECTING DEVICE

PURPOSE:To detect a voltage impressed to an alternating current passage in non-contact state while insuring sufficient insulating performance against the alternating current passage, and restrain the variation of electric field distribution around the device to be low so as to improve alternating voltage detecting accuracy by means of a photoelectric field sensor. CONSTITUTION:This alternating voltage detecting device is provided with a vessel 5 made of insulating material of which the top part 5a faced to an alternating current passage 4 is formed into a conical shape and the outer circumferential face is provided with a pleats part 5d umbrella-likely covering thereon through a decided clearance, and a condenser 10 built-in type insulating tube 9 supporting the vessel 5 with an erection base 11. A photoelectric field sensor 6 to modulate an incident light according to an electric field E generated around the passage 4 and inject it, is internally provided in the vessel 5, outside the vessel 5, a light is injected to the photoelectric field sensor 6 from an optical fiber 8 passed through the insulating tube 9, and a signal processing part 13 by which the injected light is taken in and the voltage of the passage 4 is detected by the degree of modulation of the injected light is provided.