Shuxin Luo

Implementation and Application of Practical Traveling-Wave-Based Directional Protection in UHV Transmission Lines

Traveling-wave-based protection is becoming attractive in ultra-high-voltage (UHV) transmission systems due to the requirement for high-speed protection. However, the poor transfer characteristics of coupling capacitor voltage transformers (CCVTs) for high-frequency voltage have strictly limited its application. A novel traveling-wave-based protection scheme considering the characteristics of CCVTs and current transformers is proposed in this paper. The dyadic wavelet transform is used to extract the polarities of voltage and current traveling waves for fault direction identification. A prototype is further developed for practical applications. Extensive laboratory tests are performed to assess the performance of the developed scheme. The prototype has been applied to the 750-kV substations in China and an external fault was recorded during the operation period, validating the effectiveness and reliability of the proposed protection principle.

A New Differential Protection of Transmission Line Based on Equivalent Travelling Wave

Differential protection is widely used for transmission lines, but its performance is affected by distributed capacitance current and current-transformer (CT) saturation. Travelling-wave (TW) differential protection is immune to these factors and can achieve ultra-high-speed operation. These characteristics are essential for long-distance extra/ultra-high-voltage transmission-line protection. However, the contradiction between sampling frequency and communication traffic makes it hard to ensure high sensitivity and high reliability at the same time. To solve this problem, a new TW differential protection based on equivalent travelling wave (ETW) is proposed in this paper. Wavelet transform is adopted to extract wavelet-transform modulus maxima (WTMM) of TW, which are used to reconstruct ETW. Only several WTMMs need to be exchanged with the opposite terminal, so the amount of communication is largely reduced. Current energy ratio is defined and used for operation criterion to enhance the sensitivity during faults with large fault resistance and a small fault inception angle. Detailed discussions on the selection of setting value ensure the reliability of the proposed protection scheme. Extensive simulations are conducted to test the performance of the protection. Simulation results verify that the protection can correctly discriminate between internal and external faults with high sensitivity and reliability.

Study on Travelling-wave protection Starting element

Travelling-wave starting element is an integral part of the ultra high-speed protection. Existing design method depends on engineering experience, low accuracy in travelling-wave signal recognition, easy to trip frequently or refuse to trip. To solve these problems, through mass of starting signal simulation and analysis under different fault conditions, this paper focuses on the travelling-wave starting element and figures out the travelling-wave identification method. This paper summarizes the frequency and voltage characteristics of travelling-wave head, puts forward a new method in real-time travelling-wave fault identification. In addition, the analysis course included in this paper is a useful attempt that can be used in similar fault travelling-wave analysis.

Implementation and application of practical traveling-wave-based directional protection in UHV transmission lines

Traveling-wave-based protection is becoming attractive in ultra-high-voltage (UHV) transmission systems due to the requirement for high-speed protection. However, the poor transfer characteristics of coupling capacitor voltage transformers (CCVTs) for high-frequency voltage have strictly limited its application. A novel traveling-wave-based protection scheme considering the characteristics of CCVTs and current transformers is proposed in this paper. The dyadic wavelet transform is used to extract the polarities of voltage and current traveling waves for fault direction identification. A prototype is further developed for practical applications. Extensive laboratory tests are performed to assess the performance of the developed scheme. The prototype has been applied to the 750-kV substations in China and an external fault was recorded during the operation period, validating the effectiveness and reliability of the proposed protection principle.

A non-unit protection principle based on travelling wave for HVDC transmission lines

Travelling wave protection is one of the most attractive line protection techniques in high voltage direct current (HVDC) transmission system. However, it has a low sensitivity in high impedance fault conditions as the initial wave is insignificant. This paper presents a non-unit fault protection principle based on the initial wave as well as the reflected waves to improve the protection sensitivity in high impedance faults. The reflection and refraction characteristics of the line boundaries and the fault point are analyzed to extract the features of the reflected waves, which form the principle of the protection. Furthermore, dyadic wavelet transform is utilized to detect the arrival of travelling wave surge. A simulation model based on CIGRE benchmark is built using PSCAD/EMTDC to validate the protection principle. Simulation results indicate that the proposed protection has a good performance in various fault situations especially in high impedance faults.

A Directional Protection Scheme for HVDC Transmission Lines Based on Reactive Energy

High-voltage direct-current (HVDC) transmission-line protection is becoming increasingly desirable with the expanding worldwide popularity of HVDC technologies in recent years. This paper proposes a transmission-line backup protection scheme based on the integral of reactive power for HVDC systems. The directional characteristics of reactive power flow are theoretically analyzed for internal and external faults, and these characteristics are used to construct a directional protection scheme. The Hilbert transform is adopted to calculate the reactive power, which ensures a continuous output of calculation results and improves the reliability of the protection. A bipolar 12-pulse HVDC test system based on the CIGRE benchmark is modeled using PSCAD/EMTDC, and extensive simulations of various fault situations are conducted to test the effectiveness of the proposed scheme. The simulation results show that the proposed protection scheme correctly identifies internal and external faults and performs well with different fault distances and fault resistances. Furthermore, the proposed protection is insensitive to the sampling frequency, making it practical for future applications.

Analysis of fault characteristics of half-wavelength AC transmission lines

Half-wavelength AC transmission (HWACT) is an ultra-long distance AC transmission technology, whose electrical distance is close to half-wavelength at the system power frequency. The countries with a large territory have a big demand for HWACT. The fault characteristics of an HWACT line can be different from those of a conventional transmission line. So it is necessary and significant to analyze the fault characteristics of an HWACT line. In this paper, the influence of fault distances and fault resistances on the fault voltages and currents of two buses is analyzed after different types of faults occur on an HWACT line. And the analysis results are compared with the simulation results from EMTP.

Travelling wave based directional comparison protection scheme and its application in 750 kV transmission lines

Travelling wave based line protection has the advantage in fast response speed, however, its performance in practice is still unsatisfactory due to the high frequency limitation characteristic of coupling capacitor voltage transformer (CCVT). This paper presents a directional comparison protection principle based on travelling wave, which utilizes the polarities of high frequency current and low frequency voltage, thus it is not influenced by the characteristics of CCVTs. Dyadic wavelet transform is used to extract the polarities of voltage and current increments for fault direction identification. A protection device prototype based on this principle is further developed, which has been successfully applied in 750 kV transmission system in Northwest China. An external fault record is captured by the prototype, and validates the correctness and reliability of the protection principle.

Realization and performance analysis of travelling wave based directional protection prototype

Travelling wave based protection is becoming attractive in ultra-high voltage (UHV) transmission systems due to the requirement for high-speed protection. However, the poor transfer characteristics of coupling capacitor voltage transformers (CCVTs) for high-frequency voltage have strictly limited its application. A travelling wave based protection prototype considering the characteristics of CCVTs is developed in this paper. Extensive laboratory tests are performed to assess the performance of the developed prototype. Further, the prototype has been applied in the 750 kV substations in China and an external fault was recorded during the operation period, validating the effectiveness and reliability of the proposed prototype.