Design And Application Of On-line Monitoring Device For The Insulation Condition Of Current Transformer In High-Speed Railway Substation

With the rapid development of high-speed railway, the way of preventing and repairing the electrical equipment of traction substation has been unable to meet the requirements of safety operation of high-speed railway. The on-line insulation monitoring is a new technology that the insulation of device is real-timely monitored under the operating voltage making up for the lack of the preventive trial. Current transformer (TA) is an important part of the traction network control loop, once a fault occurs, it will seriously affect the safe operation of the substation. In order to improve the operation reliability of current transformer, the paper researches and develops an online monitoring device for current transformer. The subject researches on 220kv current transformer of Xinxiang power supply section of Beijing-Guangzhou high-speed railway of Zhengzhou Railway Bureau. Study and design of the on-line monitoring device for the running state of the 220kV dry current transformer for high speed railway traction power supply equipment.Dielectric loss factor tanδ is an important parameter to reflect the insulation condition of high voltage equipment, so the on-line monitoring of dielectric loss factor tanδ is of great significance. In this paper, the design scheme of on-line monitoring device is presented and the key link of the on-line monitoring device is presented in view of the problem that the dielectric loss value Tan is not stable and the accuracy is not high enough.In the leakage current extraction process, completed the design of active zero flux single turn cored micro current sensor. Because the selection of the secondary coil turns is blind and there is no theoretical basis to fix the selection, the text proposed a algorithm to determine the optimal secondary coil turns according to the minimum excitation current principle and proved its correctness. The two turns of the sensor are optimized and the experimental verification is carried out. A zero flux principle-based active compensation method is proposed and the derivation of its working principle is done and its correctness is proved by experiment. The experimental results show that the design of current transformer compensation mode has a good compensation effect and it can obviously improve the measurement level.Designed low pass circuit that not only keeps the useful signal out of distortion but also benefits the following sample techniques. Phase lock and multiple frequency circuit diminishes the influence of frequency fluctuation to the coming calculated tan.In digital signal processing, linear FIR digital filter based on window function method eliminate the harmonics and noise interference in the collected signal. Afterward the filter is programmed with reasonable operational structure by C language and the result of MATLAB simulation suggested that the filter designed from 1280-point hamming window function is satisfactory. Aiming at the problems existing in the measurement of dielectric loss by using the harmonic analysis method, the FFT dielectric loss algorithm based on the spectral centroid method is proposed, and the frequency, amplitude and phase correction formulas are derived. Under the different conditions of frequency fluctuation, variable harmonic components and etc. in power system, the simulation is performed via MATLAB code on the conventional FFT algorithm, the interpolation algorithm with Hanning window and the algorithm in this paper, respectively. The simulation results show that the algorithm in this paper has a significant advantage in accuracy.The design of anti-interference in the application of online monitoring device is competed in the paper and the device has been put into trial operation. The actual operation results show that the insulation on-line monitoring device which is designed in this paper satisfies the accuracy and stability of monitoring data of dielectric loss value.