Zaibin Jiao

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.

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.

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 Fast Full-Line Tripping Distance Protection Method for HVDC Transmission Line

Though distance protection has been successfully used for AC transmission line, there is no practical application of it for HVDC transmission line. For distance protection, it is essential to measure accurately at the zone boundary to distinguish internal fault from external correctly, and high measurement accuracy at any part of the full line is unnecessary. Besides, HVDC transmission line is generally connected with smoothing reactor at two ends and it can be regarded as the operating boundary of distance protection. Considering these features, a fast full-line tripping distance protection method for HVDC transmission line is introduced in this paper. Based on distributed parameter model, the voltage and current at the end-point are calculated accurately using those at the relay point. After that, the line between the end-point and fault point is simplified as lumped parameter RL model and the fault distance is obtained with differential equations. In this way, high calculation accuracy at the zone boundary is attained and which contributes greatly to the improvement of protection performance. Simulation results show that this method is capable of protecting the whole line with high rapidity, and can be used as primary protection for HVDC transmission.

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.

A D-S Evidence Theory-Based Relay Protection System Hidden Failures Detection Method in Smart Grid

Hidden failures in relay protection systems are the primary factors for triggering the cascading outages and bulk blackouts of power systems, but it is difficult to detect these when power systems operate normally. In smart grids, relay protection management information systems allow us to obtain many sequence of event records under disturbances and faulty conditions. By studying such record information, this paper proposes a detection method for hidden failures based on the features of relay protection systems. In this method, certain evidence is constructed by analysis of redundancy and coordination between the primary and backup protections or within the backup protection. Meanwhile, uncertain evidence is constructed by utilizing the fault location. Then, by combining all the evidence with D-S evidence theory, detection criteria for detecting hidden failures in relay protection systems are presented. Last, the effectiveness of the proposed algorithm is verified on the IEEE 39 bus system case. The results indicate that this method can detect hidden failures in relay protection systems and send alarm information. Thus, it is of great importance to ensure the security operation of power systems in smart grids.