Research On Technology Of On-line Insulation Monitoring And Fault Location For Long Distance Power Cable

On-line insulation monitoring technique for long distance power cable is different from the short one. This is due to the cross-linked of metal sheath and voltage drop caused by load current. Twin CT method had been put forward to solve the problem of the metal sheath cross connection, which was used to measure the current flowing through the cable insulation, and introduced the principle of the method, it found that the method was suitable for all kinds of on-line insulation monitoring of power cable, whether metal sheath cross-linked or not. The methods of on-line dielectric loss factor(tan?) monitoring and cable fault location and on-line jacket insulation monitoring for long distance cable based on the principle of twin CT method were proposed in the paper.For the problem of voltage drop caused by the load current had influence on long distance power cable insulation tan??monitoring, the reference voltage selection and mathematical derivation were given and combined with the twin CT method, two terminals synchronous tan? measurement as a new method of on-line insulation monitoring had been put forward in this paper and the implementation of the method was given. The Matlab software was used to simulate the circuit of long distance three-phase cables. Simulation analysis was carried out on the method of two terminals synchronous tan? measurement, the results show that load current will not influence on tan??when choosing the half of vector sum of voltage across as voltage reference, and the simulation results were consistent with the theoretical analysis. At the same time proved that when the system existed synchronization error, voltage error, and power harmonic and frequency fluctuations has no effect on the feasibility of the method.For the long distance power cable fault location technology, two terminal synchronous fault location method based on twin CT method was proposed in the paper. The method was divided into two terminals synchronous short-circuit fault location method and two terminals partial discharge(PD) detection method, introduced the principle of two methods respectively and simulation analysis on the methods were carried out. The simulation results of short-circuit fault location method was shown that the method can accurately calculated the short-circuit point position, and proved that when the system existed synchronization error and harmonic and frequency fluctuations has no effect on the feasibility of the method, the advantage of method is not affected by transition resistance of fault point. Two terminals partial discharge detection method is according to the function of PD signal transmission and discharge point position. The test results shown that through the signal processing, it can detected PD signal on the end of coaxial cable and according to the time of signal transfer to the detection point can calculated the discharge point position. For the PD detection technology, the method combination of high frequency(HF) and ultra-high frequency(UHF) was carried out in the paper. Based on Rogowski coils of printed circuit board,a new structure field assemble of electric current sensor had been put forward, it not only can detected high frequency but also can detected power frequency signal. The PCB Rogowski coils was described in detail, including its constitute, structure, working principle and frequency characteristic. The test result shown that it had excellent linearity input-output relationship, good sensitivity and frequency characteristic, it meet the design requirements of measuring power frequency and high frequency signal. The design of UHF sensor was used to test signal from the space, and the effective wide band is from 500 to 2GHz, the test results shown that the UHF sensor had good frequency characteristic. The combination method can effectively eliminated interference, and used the signal wavelet de-noise, after that the partial discharge signal can be got.The whole hardware of the monitoring system was designed, including the signal processing circuit, the measuring and control part of circuit and the power circuit. The monitoring system was developed with the TMS320F2812 as the core of data processing and logic controlling. The ADS8364 was used for the data sampling as the A/D converter; GPS’s time function was used to provide synchronous sampling signal for system; GPRS was used for the data wireless transmission. For the software, the following function is given such as the data synchronous sampling and the main controlling, and so on. The terminal of on-line monitoring of the three-phase cable system is designed based on using LABVIEW software to design the system interface for on-line monitoring tan?? of cable insulation.The on-line monitoring system was used for the submarine oil-filled cables in Hainan Interconnection Project. According to the characteristics and operating environment of the submarine oil-filled cables, a new method of on-line jacket insulation monitoring based on twin CT method had been put forward in the paper, which was a synchronous detection technique by using four current sensors to monitor cable sheath insulation. Introduced the principle of the method and proposed the ratio of jacket insulation leakage current and the inductance coefficient of grounding circuit current which can be used to judge the jacket insulation condition. Installed the on-line monitoring system and given the monitoring results analysis. The simulation analysis was carried out on the induced and capacitive current, the simulation calculation was the consistent with the monitoring results. It can find that the method of four current sensors can accurately reflected the cable insulation condition, proved the correctness and feasibility of the method.