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The zero-sequence mutual inductance between parallel transmission lines can weaken the reliability of protective relay. As a novel zero-sequence directional element is proposed based on the model recognition theory, an inductance model is established for the internal fault. The model error is small for an internal fault while large and oscillating for an external fault. To solve the problem on the reliability and the sensitivity of the proposed method, caused by harmonics in the transient waveform, power frequency component is extracted by Fourier algorithm, least squares algorithm and fast phasor extracting algorithm separately in this paper. A 500kV parallel transmission-line model with zero-sequence mutual inductance is established in EMTP to verify performance of the proposed protective relay based on these algorithms. Each algorithm is studied by different data windows (5ms, 10ms and 20ms). Simulation result verifies the fast phasor extracting algorithm can accurately extract the power frequency component even with a short data window. And the proposed protective relay based on the fast phasor extracting algorithm has the best performance.

With the growing scale of wind power penetrated into grid, protective relays of transmission line face the challenges of adaptability. The relays based on fault component are widely used in transmission line protection, which makes it essentially important to study the adaptability of fault component protection. The adaptability of fault component protection to wind farm integration system is studied in this paper. Fault component protection works well only when the system impedance is stable or the positive and negative sequence system impedances are approximately equal. The theoretical analysis, PSCAD simulation and fault record data show that the positive sequence impedance at wind farm side has large fluctuations and obvious difference from the negative sequence impedance. This significantly reduces the reliability of the relays based on fault component in wind farm integration system.

The shunt large capacitor, on both sides of voltage source converter based HVDC (VSC-HVDC) transmission lines, will rapidly discharge to the fault point when a fault occurs. The system side can be equivalent to the shunt large capacitance in the fault component model. According to this characteristic of the VSC-HVDC system, a novel pilot protection scheme for VSC-HVDC transmission lines based on parameter identification is proposed in this paper. The protection principle can distinguish internal faults from external faults by identifying the capacitance on two terminals with the time-domain algorithm. The capacitance on two terminals can be accurately identified simultaneously when an internal fault occurs, while the capacitance at both ends cannot be accurately identified simultaneously when an external fault occurs. Therefore, a pilot protection criterion is constructed. The simulation results show that the protection scheme can distinguish internal faults from external faults reliably and quickly, and it is not affected by transition resistance, distributed capacitance of lines, and the control mode. In addition, the method can be implemented easily with simple computation and has certain practical value.

In the long-distance and extra high voltage transmission system, distance protection has been widely used. Distance protection needs to determine if a fault is internal or external to a protection zone by calculating fault distance between the relay and the fault point. In another word, quickly and accurately extracting power-frequency phasor from transient fault signals is one of the most crucial factors to distance relay protection. This paper proposes a line distance protection scheme based on Fast Phasor calculation algorithm. Firstly, the fault transient is analyzed and the accurate frequency components are obtained by using the Fast Phasor calculation algorithm. In practice, the compensation matrix in the frequency-domain is vulnerable to signals extracting accuracy and calculation speed, not meeting the requirements of protection application satisfactorily. For practical application, the distributed parameter model is implemented with Bergeron method, and the matrix of fault signals is approximated by FIR filters in the time-domain. The new method Fast Phasor calculation algorithm is based on matrix pencil method and a reduced order method is made use of in order to simplify the algorithm and thus the calculation efficiency is improved. Obviously, Fast Phasor calculation (FP) algorithm has an outstanding advantage over Least Squares Matrix Pencil (LS) algorithm and Fourier algorithm. As a result, accurate fault signals data can be acquired quickly and accurately. Then, fault location can be obtained by using conventional methods. In this paper, single-terminal electrical quantities are used in the proposed scheme. The proposed distance protection scheme is not influenced by data window as theoretical analysis shows, which can be verified by further PSCAD simulation. Three types of fault are simulated in this paper, including single-phase ground fault, two-phase ungrounded fault and three-phase fault. All the simulational results from different fault types demonstrate that the presented scheme in this paper has low computational complexity, high accuracy and high efficiency. Simulated results also show that this method is valid and is capable of detecting the faults occurring on the transmission line quickly and accurately. This distance protection scheme is of practicality and reasonability.

This paper presents a novel algorithm of distributed bus-bar protection based on admittance to solve the data out-synchronization problem of distributed differential current bus-bar protection. With the introduction of voltage, the relationship between the differential admittance and the braking admittance can be used to realize the distributed busbar protection without data synchronization. When an internal fault occurs, the differential admittance is larger than the braking admittance. When an external fault occurs, the differential admittance is far smaller than the braking admittance. According to such characteristics, the internal and external fault can be distinguished. Reflecting the grid structure, the admittance which is time-invariant, should be a constant value. Even though electrical quantity sampling of each Bay Unit (BU) are out-synchronous, the calculated results are not affected. The EMTP simulation results have proved that the calculated differential admittance and braking admittance of this algorithm are not affected by the data out-synchronization whenever an internal or external fault occurs. In addition, comparative simulation between novel principle and conventional distributed bus-bar protection are also made to analyse the data out-synchronization and other properties. Results show that this algorithm is not affected by system operation mode, less affected by transmission delay and has a high capacity against fault impedance.