Jiale Suonan

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 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.

Integrated Impedance-Based Pilot Protection Scheme for the TCSC-Compensated EHV/UHV Transmission Lines

This paper analyzes the characteristics of equivalent dynamic power frequency impedance of the thyristor-controlled series capacitor (TCSC) and the integrated impedance, which is defined as the ratio of the sum of the voltage phasors across the two ends of the transmission line to the sum of the current phasors through the two ends of the same transmission line. The integrated impedance of the transmission line is used to determine whether there is a fault inside the protected line section or not. When an external fault occurs, the integrated impedance reflects the capacitive impedance of the protected line, its imaginary part is negative, and the absolute value of its imaginary part is large. When an internal fault occurs, the imaginary part of the integrated impedance on the fault phase is either a positive value or a small negative value. According to such characteristics, internal faults can be distinguished from external faults. Based on integrated impedance, a novel pilot protection scheme for the transmission line with TCSC and controllable shunt reactor is presented. Digital simulations based on 750-kV transmission systems show that the presented scheme offers high sensitivity and reliability with many advantages over conventional current differential protection.

Real-time measurement of mean frequency in two-Machine system during power swings

This paper presents an algorithm for measuring mean frequency in two-machine system during power swings, which applies to sampled current signals in transmission lines with two sinusoidal components. The algorithm is based on rigorous mathematical deducing and recombines itself with Newton iterative technique and Taylor series expansion. The response of the algorithm is provided and the effects of key parameters, that affect the performance of the algorithm, are discussed. Computation requirements are modest and the technique has been implemented on a modern digital signal processor. The proposed technique has also been extensively tested using current signals obtained from dynamic frequency sources. Some test results are presented in the paper.

IEC 61850-Based Feeder Terminal Unit Modeling and Mapping to IEC 60870-5-104

The feeder terminal unit (FTU) is a kind of remote terminal unit along distribution feeders that allows the communication of a local process to a master or central system. In order to realize the plug-and-play function of FTUs, the FTU information models by using the IEC 61850 modeling method are proposed. And the information model and communication services model are mapped to telecontrol protocols IEC60870-5-104. The extensions to the IEC 60870-5-104 are also proposed to support the exchange of the model information. A prototype system is developed. The system demonstrated that the seamless communication between the master station and FTU can be realized using the proposed modeling and mapping methods.

A Novel Distance Protection Algorithm for the Phase-Ground Fault

Traditional distance relays often mis-operate for high transient resistance in phase-ground faults by measuring apparent impedance. To solve this problem, a novel distance protection algorithm is proposed in this paper. It is deduced in the RL lumped transmission line model and calculates the fault distance from the measuring point to the fault point by solving a linear differential equation. In addition, a protection criteria based on the comparison result between the calculated fault distance and the protective setting margin rather than the protective zone measured by apparent impedance is set up in this paper. As a result, the proposed method can avoid overreach for the given characteristics that the calculated fault distance is greater than the actual fault distance when the fault occurs next to the opposite terminal. Meanwhile, both the fundamental component and one decaying DC component are needed to solve the differential equation for the proposed distance algorithm, therefore it can trip the breaker fast during the fault transient period. Finally, EMTP simulation results verify the validity of the proposed distance algorithm on RL transmission line model. However, to put the proposed method into field use, the problem caused by the distributed capacitance of the transmission line on the proposed method will be further studied and solved.

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.