Method of detecting disconnection of optical fiber for ground fault detection signal transmission of underground power transmission line

摘要

PURPOSE:To detect the presence of absence of a disconnection of an optical fiber and to dispense with a power source for a power transmitter by photo-coupling a photo-signal proportional to an earthing current in a built-in transmission line in the ground and a photo-signal sent from a receiving terminal for detecting a disconnection of an optical fiber at a power transmitter, and receiving said photo-coupled signal. CONSTITUTION:An earthing current in a transmission line built in the ground is detected by a zero phase current transformer 1 and input to a power transmitter. This current works as a device power source 6 at the power transmitter A, thereby driving each unit. In other words, the earthing current is, through an auxiliary current transformer 2, converted to a pulse frequency by a V/f converter 3, changed into a pulse-like photo-signal at a light emitting element 4 and transmitted to a detector B at a substation through a photo-coupler 5. On the other hand, at the detector B, a photo-signal from a light emitting element 7 is always transmitted to a photo-coupler 7 in order to confirm the presence or absence of a disconnection of the optical fiber, which is sent back together with an accident current through the photo-coupler 5. Accordingly, the presence or absence of a disconnection of the optical fiber and the earthing current are detected in a central processing unit 10.