Design And Research Of On-Line Capacitive Equipment Insulation Monitoring System

Along with the development of ultrahigh voltage and large capacity in power system, thepower system accident caused by electrical equipment fault causes more and more seriousloss. Capacitive equipment is important to power transmission and transformation unit, so theon-line insulation monitoring and fault diagnosis is of great practical for realization of statemaintenance. To high voltage capacitive equipment, the dielectric loss factor tanδ is asignificant parameter which can reflect the insulating condition. By measuring tanδ, theinsulation moistened, deterioration and local defects can be found to ensure the safe operationof power system, therefore, the on-line insulation monitoring of tanδ is especially important.In this paper, an on-line insulation monitoring system of the capacitance type equipmentbased on DSP is developed to measure the dielectric loss more accurately. Because of the lackof the harmonic analytical approach, the modified harmonic analytical approach is proposedto calculate the dielectric loss factor. Analytical transformation structured by the HilbertTransformation is used to counteract the negative-frequency, simultaneously, a FIR digitalfilter with plus Hanning window is designed to wipe off the interference signal. In addition,the windowed interpolation algorithm is involved to amend the difference of the phasemeasurement caused by the frequency fluctuation. Due to the dissatisfying performance oftraditional insulation diagnosis, the fuzzy diagnosis method is involved to analyze theinsulation state of capacitive equipment.The hardware circuit of on-line monitoring system is designed in this paper.TMS320F2812(DSP) acts as the core of data processing and logic controlling. The hardwarecircuit includes the current sensor with single-turn cored structure based on the zero-fluxcurrent transformer principle, voltage sensor, preposition data processing circuit, signalsampling and converting circuit based on AD7656, CAN communication circuit and systempower supply circuit. The modular programming mothed is used in software design. Thesoftware of online monitoring system includes data sampling and converting, analyticalfiltering, digital low-pass filtering, the modified Full-wave Fourier algorithm, CANcommunication, fault diagnosis functions, and so on.Finally, a experimental set-up of the capacitive equipment is built in laboratoryconditions. It validates the designed system can effectively on-line monitor the dielectric lossfactor of the capacitive equipments. The performances of the traditional harmonic analysisalgorithm and the modified harmonic analysis algorithm are analyzed by comparing thetheoretical value with the calculating results of two different algorithms. The dielectric lossfactor of different experimental model is monitored, and the experimental results validate that the system can measure the dielectric loss factor accurately and steadily.