Huang Yizhuang

A new approach to detect transformer inrush current by applying wavelet transform

In this paper, a mother wavelet suitable for processing the transient signals of power systems is constructed according to theory of wavelet analysis, and the improved recursive wavelet transform (IRWT) is presented in order to meet the real-time demands of analyzing power system signals. At the same time, research work is carried out to detect the transformer inrush current. IRWT has been used to analyze transformer inrush current generated by PSCAD and is proved both effective and feasible.

Transient based protection using current transients

A transient based protection criterion using the wavelet transform results of current transients from the two ends or three ends (T-type line) of high voltage power transmission line is presented. According to the attenuation effects of high voltage transmission line and busbar capacitance to high-frequency current transients, differences of current transients at each end of the transmission line when in-zone faulted and out-zone faulted are analyzed and used to deduce the transient current content ratio (TCCR). Protection criterion using TCCR is proposed, and the principles of protection settings are given. Wavelet modulus maxima of current transients are used to calculate TCCR. EMTP simulations of different faults using a 100 kHz sample rate are carried out for testing and analyzing the protection criterion. The protection criterion, which is proved simple, reliable and whole-line protective, is suitable for both two-end line and T-type line.

A new fault location method

This paper describes a new fault location method-the weighted Root-MUSIC method. By weighing the results of the double end method based on the travelling wave and Root-MUSIC methods, according to the position of fault point, this method synthetizes the advantages of the two methods. The performance of this method is represented through analyzing the principles of the double end method based on the travelling wave and Root-MUSIC methods. The new method gives an accurate result wherever the fault point lies on the line, and a high sample rate is not needed. EMTP simulations are provided to substantiate the analysis in different fault position cases.

A novel unit transient based protection criterion for high-voltage power transmission line

A novel unit transient based protection criterion for high voltage power transmission line based on the wavelet transform results of voltage transient signals at each end of the line is presented. The transient voltage content ratio (TVCR) and transient voltage singularity ratio (TVSR) are deduced according to the difference of high frequency voltage transients at each end of the transmission line when in-zone faulted and out-zone faulted. Protection criterion using TVSR is proposed, and the principles of protection settings are given. The criterion is suitable for both two-end line and T-type line. Simulations of different faults and different line types are carried out for testing and analyzing the protection criterion.

A new protection criterion for high-voltage transmission line based on two-end transient signals

A new criterion of high-speed protection for high voltage transmission line based on the wavelet transform of two-end data is presented. By comparing the Lipschitz exponent and time of the wavelet modulus maxima of voltages of both ends, in-zone faults and out-zone faults and switching operations can be distinguished. Simulations are carried out for testing the criterion, and the influences of fault locations and noises are discussed.

Multifunctional directional transversal difference protection device by microcomputer

This paper describes the first successful power system device with multifunctional directional transversal difference protection in China. It realized some protection action performances which are difficult for conventional relay protection. Especially, eliminating both the voltage dead-zone and increasing action sensitivity and selectability are important improvements over conventional relay protection. By using the advantages of microcomputers, this device has created some new functions which are impossible for conventional protection, and has progressed toward the direction of multifunctionality and automation. It has been successfully in field operation in a 66 kV substation in Liaoning Province since May of 1992.<<ETX>>

Combined Control of Substation Voltage and Reactive Power Compensation by Microcomputer

Abstract A regulative rule and its characteristics for decentralized control of substation voltage and reactive power compensation by microcomputer are introduced. The hardware structure and software design are illustrated as well. The prototype of this system has been operating in Dajiaoting Substation in Beijing since September 1985. Two transformers with load tap changing (LTC) and two compensation capacitor banks in that station are under control. The operating result so far showed that the combined control rule of voltage and reactive power compensation according to the load compensation method by microcomputer is correct and reasonable. It can follow the variation of load to automatically determine the reasonable voltage that has to be maintained. The accuracy of voltage regulation can achieve 0.5% and that of reactive compensation is 5%. Its application can not only improve the voltage quality of power system, but also decrease loss of electric energy. The economic benefit is obvious.