Study On On-Line Monitoring System For High Voltage Cable's Insulation

The purpose of this paper lies in studying on on-line monitoring system for high voltage cable's insulation based on the electrical power engineering background. The mathematics model of cable's insulation system, the conversion formula for the insulation leakage current, signal extraction method and signal synchronous sample, feasible algorithm of harmonic method and dielectric loss calculating method are studied. The paper focuses on realizing the monitoring system for the main insulation and restrictive coating insulation of high voltage power cables without changing the network structure of power system by measurement of phase ground current and total ground current of split phase shield cable. The research is important to find out faults in insulation system for cable in time and ensure operation safety of electric power system.Firstly, the harmonic method is studied to develop the measuring technology of tan( and the calculating formula of tan( using quasi-synchronous method is derived out. Moreover, the validity of the method is studied by computer simulation. The relationship between ground current and current passing through main insulation and the validity of monitoring cable insulation using equivalence-capacitance method are studied. According to the mathematical model, the relationship between end socket current and current passing through cable's main insulation is derived out when the cables with incomplete phase transposition and complete phase transposition. Secondly, extraction method of socket current and voltage is studied and the six channels synchronous data acquisition system is designed. Finally, according to the result of theoretical study, a dielectric loss calculating software using the quasi-synchronous method is developed and the simulative experiment is studied. According to the requirement of the function of on-line monitoring system for high voltage cable's insulation and modularization designing method, the whole system design is divided into some function modules and modules are designed separately. Finally, each function module is integrated into the whole system design. It is discovered through some simulative tests that the measuring precision of this device can reach 10-4 when it is used for measuring tan( and satisfied with the requirement of the common project.