Jiang Xiuchen

Research for dynamic increasing transmission capacity

The Dynamic Line Rating (DLR) system can increase transmission capacity of overhead line dynamically. The system is composed of sampling terminals installed on dead-end configuration of a line and one control instrument equipped in dispatch center. The data between the sampling terminals and the control instrument is transmitted through GPRS/GSM. Then three major limitations governing the line rating limits were analyzed and stated. This paper analyzed the force balance for overhead line concerned wind speeds and wind directionin a deflection plane. On this basis, a mechanics analysis model of linepsilas tension and sags was established. Analyzed the advantages and drawbacks of some mathematic model used to calculate transmission capacity. In order that the DLR system received the optimum dynamic capacity curve, combined the WM and TS model. Finally, the necessity and significance to use DLR in power grid are presented.

Study on internal pressure measurement of vacuum interrupter

In order to measure the internal pressure by the traditional magnetron method, the vacuum tubes must be detached from interrupters and put into a solenoid coil. Thus, when the interrupters are to be refitted, their mechanical parameters must be readjusted by professional workers. In this paper, a new type of magnet coil is developed. Putting this coil onto the vacuum tubes side, and without detaching the vacuum tube from the interrupter, we can measure the internal pressure of the vacuum tube by the magnetron discharge method. Meanwhile, the measuring sensitivity of internal pressure is improved by an application of 80C196 micro-controller. Furthermore, the on-line detection of the internal pressure is a hard nut to crack. In this paper, by detecting the potential of the shield with a Pockels electric fields sensor, an on-line internal pressure detecting system is developed, and its mechanism is discussed.

Experimental study and feature extraction on UHF partial discharge detection for typical model in air

In this paper, in order to represent three kinds of typical partial discharge respectively happened in dielectric, out of dielectric and surface of dielectric, five kinds of typical partial discharge models, which included needle to plate, needle to needle, plate to plate, surface and air void, were designed and manufactured with aluminum. Based on the designed models, an experiment system of ultra high frequency partial discharge detection was comprised with non-partial discharge transformer, 2.5 GHz bandwidth oscilloscope, broad band amplifier and the developed double helical antenna. Afterwards, partial discharge experiments were carried out in air, and the method recommended in IEC60270 was referenced to measure the apparent quantity of partial discharge in pC. The experimental waveforms were given out. At last, the characteristics of the ultra high frequency signals excited by partial discharge were analyzed in time domain, frequency domain and wavelet coefficients. Using kernel principal component analysis, the feature extraction was realized. Then, several characteristics, which included deflection, protruding, frequency distributing, decay time, wavelet coefficients and so on, were proposed to describe the ultra high frequency signals. The conclusion educed in this paper is significant to research the feature extraction and pattern recognition of ultra high frequency partial discharge detection for high voltage apparatus.

Study on New Method for Measurement of Internal Pressure of Vacuum Interrupters

In this paper a new method is presented for measuring internal pressure of vacuum tubes, without using magnetic fields but using decay velocity of emission current. Firstly, 500muA emission current is used to bombard the surfaces of contacts, which removes superfluous adsorbed layers of molecules from contacts surfaces. Secondly, 35muA emission current is used to ionize the residual gas, which yields ion current. The ion current strikes the surfaces of contacts, adsorbs and then becomes new added layers of molecules, which enlarges the work function of contacts material and reduces the emission current. The decay velocity (=Deltajthetas/Deltat, where Deltajthetas decay amount, Deltat decay time) of emission current is varied with internal pressure of vacuum tubes. So with certain Deltajthetas, internal pressure can be determined by measuring Deltat. The relationship of internal pressure with Deltat is deduced in theory and validated by experiment

A new measuring method and characteristic of HVDC insulator voltage distribution

A new voltage distribution measuring method on the basis of electrostatic faradism theory is introduced. A specially designed instrument, made up of a micro-rolling-motor detector, a single-chip microcomputer unit and a speaker system, is analyzed. The detector can convert the distributed voltages of HVDC insulators to ac signals to be dealt with by the single-chip microcomputer unit. Characteristics of voltage distribution and some influencing factors are also studied. Three-dimensional voltage distribution curves showed that contamination, air humidity, space charge and the applied voltage polarity have different effects on the voltage distribution. Moreover, the voltage distribution shows a dynamic process, which is greatly different from these factors in the ac case. The current flowing into each insulator is also measured.

Multi-source separation method for partial discharge detection in substations

Partial discharge monitoring and location system at substation receives radio frequency (RF) signals emitted by partial discharge to position partial discharge using a set of omni-directional RF antenna array. As it is possible for the entire substation to have several partial discharge sources simultaneously, the basic requirement of partial discharge detection at the substation is to judge whether there are multi-source partial discharge signals, and then identify and isolate them. Based on different time domain and frequency characteristics of ultrahigh frequency (UHF) partial discharge signals generated by different partial discharge sources, we perform time-frequency analysis and fuzzy clustering over RF pulse waveforms generated by partial discharge which are continuously acquired and stored, and isolate partial discharge signals from different partial discharge sources or interferences. By this method, we can effectively isolate and accurately position multiple partial discharge sources. Our study lays the foundation for identification of partial discharge types. The feasibility of this method has been proved by field test.

Measurement of internal pressure of vacuum tubes by micro-discharge and emission current

The traditional methods for measuring internal pressure P of vacuum tubes of breakers are the magnetron and power frequency voltage withstand test. A magnet coil is needed by magnetron and only very bad tubes can be picked out by voltage withstand test. In this paper, a new method - inception voltage V_d of micro-discharge / inception voltage V_e of emission current, i.e. V_d/V_e method, is presented. It is found that by means of the relationship V_d/V_e~P, internal pressure P can be measured accurately although vacuum gap d vary from 0.2 mm~0.3 mm. By this new method, internal pressure of vacuum tubes can be measured without using magnetic coil, but with following process: firstly, when contacts is under closed situation, by screwing the nut to stretch compression spring, vacuum gap 0.2 mm~0.3 mm is obtained, secondly power frequency voltage is applied to the gap and gas adsorption layers are polished by micro-discharge current, finally the V_d and V_e of the vacuum tube is measured. Theoretical study show that the bigger the V_d/V_e is, the smaller the P is. So by measuring the value of V_d/V_e, the value of P can be obtained. The relationships of V_d,V_e,V_d/V_e with P were measured in laboratory, the test results show that the measuring ranges of P can be 10⁰ Pa ~10^-3 Pa by this new method.

Research on matching pursuit algorithm based-on Laplace wavelet for partial discharge pulse detection

A new method has been proposed for detecting partial discharge pulse under noisy and interferential condition, which is based on the matching pursuit algorithm. With a dictionary of Laplace functions, whose structure is similar to that of PD pulses, the proposed scheme can extract PD pulses from the signals within noise and interference successfully. In contrast to the other methods, the new way is easy to realize and can obtain more information of PD, such as the time of occurrence, frequency component, damping rate and so on, which are useful for location, classification and identification of PD pulses. The extraction results of simulation and field experiment data revealed that the effect of extracting PD pulses is very satisfactory with the proposed algorithm.

Acoustic-electrical based detection system for partial discharge localization of GIS

A portal acoustic-electrical system for partial discharge localization of GIS is developed, which can be used for multi-channel acoustic-electrical detection of ultrahigh-frequency, ultrahigh-current and ultrasonic signals generated by partial discharge of GIS. The system program, developed based on LabVIEW, is able to continuously capture, sample and store pulse waveforms of partial discharge signals. It can also calculate the phase of discharge pulse, and analyze time-frequency & amplitude-phase distribution of partial discharge signals. By calculating time difference between ultrahigh frequency signals & ultrasonic signals of partial discharge or between ultrahigh frequency signal and ultrasonic signal by multiple-channel detection, this portable acoustic-electrical system can achieve localization of partial discharge. Our system has been applied in partial discharge localization at several 220kV and 500kV GIS substations. The detection results verified the performance of this portable acoustic-electrical detection system.

Sensitive insulator-a new method to detect the faulty porcelain suspension insulator

The porcelain suspension insulators are destroyed by mechanical power, alternation of cool-heat while running on the transmission line, which leads to power faults. Finding the faulty insulator out before the fault occurs becomes more and more important. At present the most useful method is to measure the distributed voltage which is not refined. Therefore a new method is developed. When there is a faulty insulator, the distributed voltage of other fine insulators will change. Moreover the changing degree is different according to the damaged degree and the location of the faulty insulator. But there is always a sensitive insulator when the faulty insulator is rather dangerous. Measuring the voltage of that insulator can make the status of the others clear. In the laboratory, the situations of 110 kV and 220 kV have been simulated and the conclusions have been obtained. The distribution voltage of the 4/sup th/ insulator from the earth is the sensitive insulator. The threshold is 6%, if the measured voltage of 4/sup th/ insulator is 6% higher than the standard voltage, there must be a faulty insulator in the string.