Optical fiber composite overhead ground wire (OPGW), as a new type of single side ground wire for 110kV and above high voltage transmission lines, has been widely used for its high reliability, superior mechanical performance and low cost. In order to protect the transmission line from lightning stroke, two overhead ground wires are usually set up on the top of the tower, one is parallel ground wire, generally steel strand, the other is OPGW cable hardware, which runs through the whole line. Considering the discharge current of grounding wire in case of short circuit and lightning stroke, OPGW is usually grounded one by one.
When grounding, the electromotive force generated by the current of the conductor on the ground wire will inevitably generate current, thus generating electric energy loss. For a long time, the induced current of ground wire has been considered as a disadvantage factor, which can be effectively used in practice, and provides a solution for the power supply of high-voltage transmission line on-line equipment. According to Maxwell's principle, when a conductor flows through an alternating current, an alternating magnetic field will be generated in space. When the alternating magnetic field cuts a space closed plane composed of two lightning protection grounding wires and a tower, the induced electromotive force will be generated in the plane. Once the conductors in the plane form a loop, the induced loop will form in the plane.
The basic principle of ground induction power supply is shown in Figure 1. The power supply consists of two parts: power transformer group and back-end circuit. The power incoming current transformer group adopts two-stage current transformer topology structure, that is, it is composed of multiple primary incoming current transformers with different saturation characteristics and one secondary energy absorption transformer; the back-end circuit mainly realizes protection, rectification, power monitoring, stable energy storage, and stable DC power output. From the domestic and foreign literature, most of the transmission line online monitoring systems using coupling technology adopt high-voltage coupling mode. However, there are few researches on the induction extraction technology of OPGW at home and abroad. The transmission line online measurement device developed by usi power company based on high voltage current induction technology works reliably, with the minimum primary current of 50A. When the primary current is less than 50a, PD2 is powered by built-in lithium battery, which provides 12h power supply, and then switches to the low power consumption mode, and turns off the power system step by step; when the primary current reaches 120a, the induction charging module starts to charge the lithium battery Electricity. The mass of the whole set of equipment is 10kg. From the above technical parameters, we can draw the following conclusions: at present, the line measurement equipment based on the coupling power supply has entered the practical stage in foreign countries, which seems to have some shortcomings: 1) the adaptability of OPGW cable fittings to the primary current is still limited, the minimum current can only reach 50a, and under 50a, it needs the power of lithium battery, and the lithium battery can only be charged by 120a · h equipment, so the equipment in a certain degree The lifetime of lithium battery will also be affected when it is used in the layer.