Shenxing Shi

Identifying Single-Phase-to-Ground Fault Feeder in Neutral Noneffectively Grounded Distribution System Using Wavelet Transform

A scheme of single-phase-to-ground fault feeder identification in distribution networks with the application of a wavelet transform technique is presented in this paper. The scheme uses zero-sequence current traveling waves to identify the faulted feeder, and the busbar residual voltage to determine an event caused by fault or switch operation. The current traveling waves measured by zero-sequence current transducers are decomposed using wavelet multiresolution analysis. The local modulus maxima of the wavelet transform are extracted to determine the time of the initial traveling wave. The wavelet transforms on all feeders at the time are compared in magnitude and polarity with each other to identify the faulted feeder. The feeder identification is independent of the network neutral-point grounding mode. The proposed scheme was implemented and verified using Electromagnetic Transients Program (EMTP)-generated signals. The scheme proved to be robust against transients generated during normal events, such as feeder energizing and de-energizing as well as capacitor bank switching.

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.

Non-communication protection of distribution feeders with tapped-off-loads

This paper presents a new technique for the accelerated protection of distribution systems with tapped-off-loads. In the technique, the sequence and superimposed signals are used to determine the remote circuit breaker operation, from which whether a fault is inside the protected section can be derived. Extensive simulation studies with respect to a typical double end feeder system with tapped-off-loads show that the proposed technique is able to significantly increase the speed of response of the conventional time grading based protection scheme.

Traveling wave based single-phase-to-ground protection method for power distribution system

Correct detection and identification of single-phase to-ground faults not effectively grounded in distribution systems is a major challenge for protection engineers. This paper proposes a novel traveling wave based protection method to solve this problem. The proposed method compares the polarities of current and voltage traveling waves measured immediately after the fault inception to determine the fault direction. Nuisance tripping is avoided by using the power frequency voltages detected on the busbar to inhibit operation. The power frequency voltages ensure that the system does not mal-operate due to noise and also provide discrimination for phase-to-phase and three-phase faults. The wavelet transform and modulus maxima theories are used to extract the polarity of traveling waves measured at the relaying point. The simulation studies demonstrate correct operation of protection, which is independent of fault distance, fault inception angle, fault path resistance, and the method used for neutral grounding.

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.

Research on the process of power flow transferring and its identification method

This paper analyzes the general process of power flow transferring and divides it into four parts: 1) the process of first phase selection after fault occurs; 2) the process of selective action at the first time; 3) the process of second phase selection and status confirmation; 4) the process after status confirmation. It points out that the issue of asymmetrical flow transferring is a critical process which must be put emphasis on. Then it proposes a method to identify this process, and discuss different solution methods.

A novel current travelling wave based single-ended fault location method for locating single-phase-to-ground fault of transmission line

Current travelling wave based single-ended fault location method needs to recognize the travelling waves propagating from the fault direction as well as the travelling wave reflected from the fault point or remote-end bus. This paper firstly compares the current travelling waves of the fault line and the longest health line connected to the local bus based on dyadic wavelet transform to obtain the current travelling waves propagating from the fault direction. Secondly, based on the cross transmission phenomenon of modal travelling waves under the scenario of single-phase-to-ground fault, the arrival sequence relation and the polarity relation of aerial-modal component and zero-to-aerial-modal component (i.e. cross transmission component) of the current travelling waves reflected from the fault point and the remote-end bus are investigated and the source of the second current travelling wave propagating from the fault direction is identified. Thirdly, the first and the second current travelling waves propagating from the fault direction are utilised to locate the single-phase-to-ground fault. Finally, a large number of EMTP based simulation cases are used to test and validate the proposed fault location method.

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.

Applicable range analysis of optimized single-terminal fault location algorithm

Impedance method and single terminal travelling wave method are analyzed in paper, applicable scope of optimized solution is presented. Impedance method is of high robustness but low accuracy. Single terminal travelling wave method offers high accuracy but poor robustness. Optimized solution combines these two methods together, takes advantages of both methods. It is a great enhancement to single terminal fault location. This paper analyzed theoretical basis of optimized solution, proposed the calculation algorithm of fault location range using impedance method. Analyses of impedance method and single terminal travelling wave method show that the optimized solution is suitable for engineering application. Error analysis is proved correct by simulation.

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.