Xiaoning Kang

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 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 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.

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.

A Model Parameter Identification Based Bus-bar Protection Principle

A novel model parameter identification based bus-bar protection principle is proposed in this paper. An inductance model can be developed when an internal fault occurs on bus. By taking the inductance and the resistance of the model as the unknown parameters to be identified, the equivalent instantaneous impedance and the dispersion of the parameter can be calculated. Utilizing their difference, the external fault and the internal fault with different current transformer (CT) saturation extent can be distinguished correctly. Based on this, a new criterion with self-adaptive restraint characteristic for busbar protection is put forward. As the new principle is suitable for non-periodic component, fundamental component and harmonic component, it can operate more rapidly comparing with the traditional phasor based bus-bar protection principles. Moreover, the proposed principle has the inherent immunity to the impact of fault current flowing out when a fault occurs in the protection zone of the breaker-and-a-half bus-bar and is insensitive to fault resistance. Simulation results show that the presented principle has high sensitivity and reliability.

An accurate fault location algorithm based on parameter identification of linear differential equation using one terminal data

In this paper, an accurate single-ended fault location algorithm using linear differential equations is introduced. Based on the R-L model of transmission lines, this algorithm is inferred from the differential equations of fault network and fault components network. The fault location linear differential equation takes the fault distance, fault resistance and source impedance (a resistance and an inductance here) of system after fault point as unknown variables. Seek these four unknown variables from the solution of coefficients of the fault location equation. This method does not need iteration and initial value and is helpful in distance relay because of the uniqueness of its solution. Simulation results prove the high accuracy and low computational costs of this algorithm. Variations of source impedance and fluctuations in power frequency have no effect in fault location result. The algorithm is suitable in all fault types.

One-Terminal Impedance Fault Location Algorithm for Single Phase to Earth Fault of Transmission Line

Considering that the single-phase to earth fault is the main fault type on overhead transmission lines, the single-phase reclosure (SPR) scheme is applied widely to improve the stability of power system in China. Utilizing one-terminal post-fault measurements before the faulty phase is tripped and the measurements of the sound phases when the tripped faulty phase is waiting for SPR, the fault resistance and remote end source impedances can be calculated exactly, and a novel one-terminal impedance fault location algorithm based on SPR for the single-phase to earth fault is presented. By using alternative transient program (ATP), a distributed parameter line model based on the real transmission system parameters is employed for demonstrating the effectiveness of the new method, and the simulation results have shown the good performance of the proposed algorithm.

Protection technique based on parameter identification — its principle and application

A novel protection technique using parameter identification is proposed. According to the electric network theory, there are fixed relationships among the stimulated signals, the network parameters and the actual responses. This means that it is possible to identify the network parameters using measurement data from stimulation and network response. Any electric component to be protected can be considered as an electric network. When a fault occur, no matter inside or outside the component, the fault transient, i.e. response, can be used to identify the parameters. Comparing the calculated parameters with their normal values, the fault can be detected. Recent research indicates that some engineering problems in protection, such as the accurate fault location using local data, the instantaneous directional component, the fault identification of series compensated transmission lines and the fault line selection in the non-solid earthed network, can be solved by using the proposed principle. With the application of optical transducers, this protection principle could have great potential for practical applications.

Novel Transmission-Line Pilot Protection Based on Frequency-Domain Model Recognition

Accurate frequency components of fault transient signals can be analyzed by the Matrix Pencil algorithm. By means of the Matrix Pencil algorithm, a new pilot protection principle for transmission lines based on frequency-domain model recognition is presented in this paper. First, the frequency-domain models at the internal and external state are built. Then, two model errors are defined for the two models to distinguish internal faults from external faults since the characteristics of the two frequency-domain models are opposite. For an internal fault, the fault data satisfy the internal fault model, and the internal fault-based model error is equal to zero. While for an external fault, the fault data satisfy the external fault model, and the external fault-based model error is equal to zero. Thus, the fault can be distinguished easily by model recognition. Besides the fundamental frequency component, an aperiodic component and other frequency components extracted by the Matrix Pencil algorithm are also applied in the protection to make the principle suitable in fault steady and fault transient state. Eventually, data from both Electromagnetic Transients Program simulation and dynamic physical simulation demonstrate that the novel pilot principle can detect the internal fault quickly and reliably, immune to the impacts of capacitive current and transition resistances.