Liang Cong

The relationship research between the permittivity and internal pressure in vacuum interrupters

The Vacuum Circuit Breakers (VCBs) are typical types in the medium voltage distribution switches, and the internal pressure (P) in the vacuum interrupters affects the working quality and life. With the development of national smart power grids and the maintenance system based on reliability, on-line monitoring of the internal pressure in the vacuum interrupters becomes necessary and urgent. With the increasing of voltage level in VCBs, requirements of, internal pressure on-line diagnosis devices were highly recommended by Smart Grid, especially for the 35kV, 72.5kV and above voltage level. At present, the popular domestic on-line monitoring methods are achieved by detecting the potential of vacuum interrupter shield (Uc), the solving analysis of Uc makes significance meaning to the on-line monitor theory of the internal pressure. The relationship of the internal pressure(P) and sr was studied, the expression of P and 8r was concluded on dry air condition, and emulation mode conditions was provided for studying the relationships of internal pressure(P) and potential of vacuum interrupter shield(Uc). Necessary theoretical and technical support was supplied for the intelligence and condition-based maintenance for VCBs, and this work is valuable for reference engineering application.

Triggering characteristic of TVS and its application research in synthetic making test for high voltage circuit-breakers

Triggered vacuum switches (TVS), have found fast growing applications in the field of power system and pulse power. The key to perform synthetic making test at full rated voltage for high voltage switches is the making device of current source, so the chief aim of this research is to investigate the triggering feature of TVS, a series experiments have been carried out on the sample TVS especially with AC load between the main electrodes. The triggering and delay characteristics were emphatically expounded. An elaborated circuit for controlling the TVS is proposed herein. The triggering energy of the controller can be adjusted conveniently. By means of changing the triggering energy, the experimental results show that the delay and jitter times decrease with increasing trigger energy. The delay and jitter times decreases magnificently with the increasing voltage in the main gap. By increasing the main-gap voltage, the triggered probability increases. At last, theoretically and experimental research has been carried out of TVS used for high voltage circuit breakers synthetic making test equipment. The analyzing and test results are presented also, and which indicate TVS was suitable for high voltage circuit breakers synthetic making test.

A high accurate sensor research and its application for VCBs' internal pressure on-line condition monitor

To improve the intelligence and reliability of the vacuum circuit breakers in power gird, a high accurate smart system was designed for On-line condition monitor of vacuum interrupters inner pressure. Through the study of dielectric theory and exploration of the inherent laws of shield potential with different pressure in VIs, it shows that with the deterioration of internal pressure the AC component on shield potential increase while the pressure stays lower than 0.1Pa and the DC component appears when the pressure increases to 0.1Pa. The structure, size and installation location of the sensor were designed with reasonable calculation to detect the weak changing signal. To meet the requirements of sampling signal characteristics, digital filter was developed to eliminate noise interference, the processed signal shows good smoothness and linearity after filtered. Fast Fourier transform (FFT) method is adopted to extract the amplitude of AC component on the shield potential, and fitting the empirical formula is derived based on the offline curve of AC component increment and inner pressure of VIs. Applying the previous theoretical studies to actual 10kV VCB on-line condition monitoring system design, focus was placed on the AC component of shield potential in the monitor devices. The feasibility of the sensor and transformation algorithm was proved in the end of this research.

The assessment and prediction method for VCB contact endurance research based on LM-BP neural network

The LM-BP neural network prediction model for contact system electrical endurance of vacuum circuit-breakers is established, which based on the electrical endurance curve and the advanced breaking current weighted cumulative method (BCWC). The influencing factors that affect the prediction of VCBs electrical wear were researched. Then the LM-BP algorithm iterative process of contact electrical wear is significantly analyzed, and the detailed process of establishing the LM-BP electrical endurance model is presented also. Furthermore, the technique and the cautions of selecting hidden layer neurons and confirming of hidden layer node number during the process of establishing the LM-BP model are specially analyzed. At last, the neural network training and prediction has been carried out based on the obtained samples. The relative error of desired output and actual output is analyzed and the corresponding results are presented also. The results show that the LM-BP neural network of VCBs contact system, discussed in the paper, can accurately predict the residual contact wear. And the method provided in the paper presents not only a new idea to the on-line condition monitoring of the electrical endurance of VCBs contact system, but also valuable for engineering application of on-line monitoring and forecasting.

The relationship research between the internal pressure and shield potential in vacuum interrupters

Potential on middle shield of vacuum interrupter is one of techniques to determine the degradation of pressure in vacuum interrupters. Extensive research on the component of the shield potential and the cause of its conformation was done, certain results were obtained in theory and experiments. However, among multiple interpretations in causes of interrupter shield potential, there are still no accepted standards, and it is difficult to dealing with different types of circuit breakers according to the same standards in practical application. Seek out the mechanism relationship between the shield potential and internal pressure. This paper starting with the relevant electromagnetic theory and Gas discharge theory, the degradation of the internal pressure process was divided into three phases as discussed, and the theoretical basis of each stages based on was described. In particular the pressure in vacuum interrupters is lower than 0.1 Pa when potential value of the shield is more difficult to determine, 3D finite element method was used to calculate the shield potential in it, variation of shielding potential in this vacuum range was analyzed, result of the research provides a method to determine the feasibility and assessment of internal pressure, with good application reference value.

The method of power capacitor partial discharge signal extraction based on several algorithms fusion

Partial discharge (PD) is the initial sign of power capacitor insulation failure, and an effective extraction and analysis method of PD signal in power capacitor can improve the effectiveness of the on-line fault monitoring. The method which based on wavelet threshold denoising and mathematical morphology alternate mixing filter is put forward in this paper. First, the PD signal which includes noise is wavelet decomposed with the proper wavelet function and scale, and each layer of wavelet coefficients is extracted. Then appropriate flat structure element is chosen aimed at the scales of wavelet coefficients, and the mathematical morphology alternate mixing filter is used to filter out the noise and get a new wavelet coefficients. Choosing the appropriate threshold rules for the new wavelet coefficients, the wavelet coefficients after the threshold treatment is wavelet reconstructed and the PD signal after denoising is got. The wave distortion mean square error eMSE and SNR are chosen as the indicators to analyze and compare the denoising effects of wavelet threshold denoising method and the fusion denoising method. The results show that the fusion method can effectively remove the noise and keep the original shape characteristic of the signal better.

VCB contact system electrical endurance on-line condition monitoring technology and its application

In order to reduce the number of accidents and prevent possible troubles due to the failures of VCBs, one valid way is to monitor their performance and condition on-line. Based on the understanding and development of condition based maintenance (CBM) of high-voltage circuit breakers, the authors give some general introduction to electrical endurance on-line condition monitor for VCBs, in which the stress put on the non-intrusive method and device for determination of the arcing duration. The principle and configuration for arcing duration detect are emphatically expounded in our research, in which the electromagnetic induction theory is adopted for the arcing initialization and duration detect. The simulation and experimental results of the arcing detect device are provided in detail. The accuracy and stability of the arcing detect device have been demonstrated and it can distinguish co-existing arc signals in three-phase of circuit breakers. In the end, an algorithm for the electrical endurance of vacuum circuit breakers on-line condition monitoring system is proposed, which based on TMS320F2812 one type of DSP281X series produced by Texas Instruments semiconductor. The universally accepted approach of accumulative breaking current of high voltage circuit breaker contact to diagnose electrical endurance is used in the High-voltage Circuit Breakers Electrical Endurance On-line Monitor system.

The least squares method for VCB electrical endurance parameters predicting research based on breaking current weighted cumulative method

Calculating method of the current index alpha and the theoretical total wear Q is emphatically analyzed based on the electrical endurance curve, which adopt advanced breaking current weighted cumulative method (BCWC) used for predicting the remaining electrical endurance of vacuum circuit breaker (VCBs) contact system. The purpose of this work is to provide a clear and concise engineering description for VCBs contact system on-line monitoring practically. The mathematical and theoretical model of electrical endurance for VCBs contact system is established. The current index alpha and the theoretical wear Q are analyzed in detail based on the method of least squares. Then the parameters predicting method used for prognosticating remaining electrical endurance is proposed. Comparative study was carried out, through which the validity and feasibility of researched method can be verified. The results of this work show that the achievement and the researched procedure are correct and reasonable, which indicate the total wear of a VCB contact system is certain once contact material and structure type is determined. Moreover, based on the method provided, the relation between breaking current and already operation time is also can be gained. So the current index alpha and the theoretical wear Q applying to the advanced breaking current weighted cumulative method are obtained. Finally, the hardware and software for VCB contact system electrical wear on-line monitoring device is fulfilled based on the research results mentioned above. This work can provide some reference for engineering application for electrical endurance on-line monitoring of VCBs contact system.

A VCB and IGBT based combination switch and its application in power quality improvement

A new type controlled switching device is introduced, which based on vacuum circuit-breaker (VCB) and power electronic switch(IGBT) to form the combination switch module. The structure and working principle of provided combination switch were emphatically expounded, especially the open and closing process and controlling strategy were discussed in detail. The researched VCB with permanent magnet actuator, and the synchronous controller of combination switch module based on the digital signal processor, in which the algorithm of average series for zero-crossover phase difference is adopted, so the phase information of power grid can be extracted rapidly and accurately, and synchronous tracing pulses can be procreated. When remote control instructions are received, according to the phase information of power grid the combination switch acts synchronously to ensure that the operation time of combination switch opened and closed in right position. The application of introduced combination switch for power quality control and improvement is present in this research also. In this control device, the real-time acquisition of electrical parameters is adopted and the crossover point of reference signal is detected by average series for zero-crossover phase difference algorithm. Accompanied with improved appropriate switching strategy, the device can operate shunt capacitor banks on expected target point.