Guobing Song

Parallel transmission lines fault location algorithm based on differential component net

This paper presents a novel time-domain fault location algorithm for parallel transmission lines using two terminal currents. Parallel transmission lines with faults can be decoupled into the common component net and differential component net. Since the differential component net is only composed of the parallel lines and its terminal voltages equal zero, the proposed algorithm is based on the fact that the difference between voltage distributions, calculated from two terminal currents, is the smallest at fault point. To be practical, unsynchronized data and the transient transferring ability of the current transformer are taken into consideration. The algorithm needs a very short data window, and any segment of current data can be used to locate faults. The proposed algorithm is verified successfully using the simulation data generated by the frequency-dependent line model of the Alternative Transients Program and the field recording data provided by traveling-wave fault locators. Locating results show the satisfactory accuracy of the algorithm for various fault types, fault distances, and fault resistances.

A Novel Fault-Location Method for HVDC Transmission Lines

This paper presents a method for locating faults on HVDC transmission lines using two terminal data. Different from those based on the traveling wave principle, the new fault-location algorithm can use any section of the postfault data to locate faults. The proposed method is developed based on the distributed parameter line model in which the voltage distribution over the line can be obtained from the voltage and current measurements at both terminals and point where fault occurs can be identified from the calculated voltage distribution. The fault-location algorithm is performed in time domain and thus a short data window is sufficient for it to achieve satisfactory accuracy in practice. The proposed algorithm is simulated using data of the frequency-dependent line model in EMTDC and data of an existing HVDC line as well. The simulations have shown that this method is valid and is capable of locating the faults occurring on HVDC transmission lines quickly and accurately.

A Novel UHV/EHV Transmission-Line Pilot Protection Based on Fault Component Integrated Impedance

Based on the ratio of the sum of the fault component voltage phasors across the two terminals in the transmission line to the sum of the current phasors through the same line, which is defined as fault component integrated impedance in this paper, a new transmission-line pilot protection principle is proposed. When an external fault occurs, the amplitude of the fault component integrated impedance that reflects the capacitance impedance of the line becomes large; When an internal fault occurs, the amplitude of the fault component integrated impedance which reflects the impedance of the system source and the line, becomes relatively small. Therefore, the fault in the line can be detected according to this characteristic. The criterion is not affected by the current through the capacitance and is not affected by the fault resistance. It can be applied to the line with or without shunt reactor. Also, it can be easily set. Both the simulation results with Electromagnetic Transients Program and dynamic model data verify the validity of the proposed principle.

Distance Protection for HVDC Transmission Lines Considering Frequency-Dependent Parameters

For distance protection, the measurement accuracy at the boundary of protective zone is the most important issue to distinguish internal faults from external faults correctly. Since the line parameters depend strongly on the frequencies, in order to obtain high accuracy, it should be considered during initial fault transients generally associated with plentiful harmonics. In this paper, a distance protection method considering a frequency-dependent parameters is introduced into HVDC transmission lines. According to transmission-line equations, the frequency-dependent parameter model is separated into two parts: 1) distributed parameter model and 2) a compensation matrix related to frequency-dependent parameters, and the latter is approximated in the time domain with finite impulse response filters. So the voltage and current at the setting point are calculated accurately using local sampling data, and the fault distance is obtained by solving differential equations. The proposed algorithm is able to enhance the calculation accuracy of fault distance greatly at the remote-end faults. Furthermore, it is performed in the time domain and, thus, a short data window is sufficient for it to achieve satisfactory accuracy. Simulation results show that this method is valid and is capable of detecting the faults occurring on the protected line quickly and accurately.

A New Whole-Line Quick-Action Protection Principle for HVDC Transmission Lines Using One-End Current

HVDC transmission systems have found wide applications in modern power systems and have produced a useful influence on the stability and security of power systems. The currently used protections for HVDC systems operate on the principles which have poor reliability and inadequate sensitivity. To overcome these problems, this paper presents a new whole-line quick-action protection principle for HVDC transmission lines. The proposed method, based on the boundary characteristics of the line, can distinguish internal faults from external ones using single-terminal current measurements only. The criterion of this protection has been formulated. Simulations on frequency-dependent parameter-line model and the field-recorded data of a ±500-kV HVDC system show that this method is valid and feasible. The proposed protection, sound and clear in principle and easy to implement, can be expected to become a primary protection of HVDC transmission.

A Novel Single-Phase Adaptive Reclosure Scheme for Transmission Lines With Shunt Reactors

Single-phase adaptive reclosure (SPAR) schemes applied to transmission lines have been an effective method to improve the stability of power system. Attractive techniques have been proposed for SPAR schemes based on the tripped fault-phase voltage. But for transmission lines with shunt reactors, the voltage is so minor that the error of voltage transformer limits the applications of voltage-based SPAR schemes. To overcome this disadvantage, a new scheme using differential current between the calculated current based on transient fault model and the actual measured current from the fault phase of shunt reactor is proposed in this paper. The calculated current is obtained by using the transient fault model whether there is a transient or permanent fault. In the case of transient fault, the calculated current is close to the measured current due to the actual fault model being close to the calculated model. As for the permanent fault, the calculated current is quite different from the measured current. Therefore, the differential current of the fault phase can be employed to distinguish permanent fault from transient fault. At last, the Alternative Transients Program simulation results show that the developed algorithm can identify the permanent fault correctly and reliably, and is promised to be applied to SPAR for transmission lines with shunt reactors.

Novel Distance Protection Based on Distributed Parameter Model for Long-Distance Transmission Lines

Traditional distance protections mainly use a lumped parameter model and perform poorly under high-resistance ground fault and/or for long-distance transmission line. In order to overcome the defects, this paper presents a new distance protection method, which is developed based on the distributed-parameter transmission-line model and can distinguish internal faults from external faults based on the trend of the voltage distribution in the neighborhood of the setting point of protection. The criterion of this new distance protection is also put forward. The effectiveness of the proposed method and the error involved are discussed in detail. This new distance protection is simple in principle and easy to implement. In addition, without having to calculate the voltage distribution along the entire line, this algorithm has low computational complexity. In particular, the proposed distance protection still operates correctly under high-transition-resistance faults. Both simulations in distributed parameter transmission-line models and 750-kV power-line field data have demonstrated validity and feasibility of the proposed protection method.

Natural frequency based protection and fault location for VSC-HVDC transmission lines

With excellent priorities, Voltage Source Converter based HVDC (VSC-HVDC) will be the promising offset of HVDC transmission technology. This paper presents a protection and fault location method for VSC-HVDC transmission lines using one terminal current data. The proposed method is based on the natural frequency from the reflection process of traveling wave on a distributed parameters transmission line. As the presence of the large shunt capacitor on both terminals of the VSC-HVDC lines, the high frequency traveling wave is close to total reflection on the terminals. Therefore, the value of natural frequency of VSC-HVDC transmission lines is only related to fault distance and travelling wave speed, and the magnitude of natural frequency signal is related to the fault resistance. According to these characteristic, a single-end protection and fault location method is proposed. Compared with traveling wave method, the proposed natural frequency method is more simple and reliable. It does not need to detect accurate wave-front arriving instant with high sampling frequency. The proposed method is verified using the frequency-dependent line model in EMTDC. The simulations have shown that this method is valid and is capable of locating the faults occurring on VSC-HVDC transmission lines quickly and accurately.

A Novel Busbar Protection Based on Fault Component Integrated Impedance

This paper describes a novel principle for protecting busbars. The principle uses the ratio between the fault component voltage and the fault component differential current of the busbar to detect faults, which is defined as the fault component integrated impedance in this paper. The fault component integrated impedance of an external fault reflects the capacitance impedance of the busbar whereas that of an internal fault reflects the parallel connection result of the impedances of all the feeders connected to the busbar. As a result, the magnitudes of the integrated impedances are quite different between an external fault and an internal fault. According to such a characteristic, the criterion of fault detection is put forward, which has the inherent immunity to the impact of current flowing out when a fault occurs in the protection zone of the breaker-and-a-half busbar and is insensitive to fault resistance. The impact of the current transformer (CT) saturation on the proposed principle is discussed in this paper. Following the changes on the argument of the fault component integrated impedance, a feasible CT saturation detection algorithm is presented. EMTP simulation results verify the sensitivity and reliability of the proposed principle.

Modeling and Fault Analysis of Doubly Fed Induction Generators for Gansu Wind Farm Application

Wind power is developing rapidly as a means of handling the worlds energy shortage and associated environmental problems. The Gansu provincial wind energy resources have around 237-GW wind power potential in China. In this paper, a study on key technologies of Hexi 750-kV power transmission line protections has been carried out. The project includes some characteristics, such as large-scale wind power, long-distance EHV lines, and so on. We used 49.5-MW doubly fed induction generator (DFIG) wind turbines in this project and different situations when a fault occurs in the presence of DFIG are studied and investigated. By the aid of stator-flux-oriented vector strategy, the system is modeled in PSCAD/EMTDC software on the basis of the real information from the wind farm site. The fault analysis is studied while the fault location is changed and the crowbar protection is ON/OFF. The data and information have been obtained by field experience of the wind farm in Gansu province. Also, the matrix pencil algorithm has been applied as a novel method in this project. This analysis can ease the protection issues and push the schedule to the next steps. With these results, we are able to adapt our system with smart grids and provide some novel methods to stabilize and control the wind farm.