A. Klimek

Integrated protection of power systems

This paper reports on the development of integrated protection for power system. The concept of integrated protection is introduced, in which a centralized protection system (or relay) provides the protection of multiple power plant or a substation. Examples are given of the protection schemes with the features of integrated protection which are currently under development. A novel integrated protection scheme for substation and network protection is described. The technique is based on the detection and processing of fault generated transient current signals, in which specially designed protection relays are installed at each substation of a network. The transient detection unit of the relay detects the fault generated transient current signals. The transient polarity identification algorithm is then applied to the transient signals to identify the polarity of the signal detected. The direction of a fault is determined by comparison of the polarity of the signals derived from all the line sections connected to the substation. The actual faulted section is identified by processing the directional information from various substations

Negative-Sequence Pilot Protection With Applications in Open-Phase Transmission Lines

Negative-sequence pilot protection (NSPP) is one of the most widely used protective principles for high-voltage/extra high-voltage transmission lines due to its excellent properties. Properties, such as immunity to system oscillation and the fact that it is not influenced by shunt capacitance, make it especially valuable for the protection of long-distances ultra-high voltage lines, which transfer large amounts of energy. However, negative-sequence pilot protection (NSPP) is not suitable for applications when a system operates with one phase open, which inevitably limits its overall application. To solve this problem and to achieve the selectivity and sensitivity for the NSPP algorithm, a novel algorithm for NSPP is proposed in this paper, which takes the load-phase voltage into the calculation of the negative-sequence voltage with a fault in the open-phase condition, and compensates the negative-sequence current in the open-phase operations for phase-ground faults. Simulation studies show that the proposed algorithm is able to produce excellent performance.

A New Current Differential Protection Scheme for Two-Terminal Transmission Lines

This paper describes a new current differential relay. A current differential plane is presented firstly to depict different system statuses. Two traditional current differential protection schemes are discussed by plotting their operating and restraint region in the current-differential plane. A relay characteristic with more appropriate operating and restraint region is plotted in the plane by analyzing the tolerances a current differential relay has. Based on the analysis, a new scheme of current differential protection is designed. It is tolerant of channel delay asymmetry, power system impedance nonhomogeneity and CT saturation. Finally we prove the relay performance using simulations. It enhances current differential relay performance without a significant increase in cost.

Simulation and algorithm development of protection scheme in DC traction system

This paper presents a simulation model of DC traction system which is based on bilateral power supply mode. The model of two substation rectifiers in one track section has been proposed which is according to practical situation. The modeling was conducted with respect to the variations of the starting-up process and short circuit conditions. By comparing and investigating the simulation results of short circuit current and the train starting current, more effective algorithms such as DDL protection has been proposed. The paper presents the principle and analysis of DDL protection scheme, which shows effectiveness of DDL protection for fault detection and discrimination against train starting currents in the DC transit system.

Evaluation of an Accelerated Overcurrent Protection for Single Circuit Breaker Distribution Feeder

This paper presents a new practical accelerated overcurrent protection scheme for single circuit breaker radial distribution feeder and the implementation of this new scheme into latest numerical relay. Extensive tests have been conducted using the real time digital simulator (RTDS) with respect to a typical single circuit breaker multi-section system. The results prove that the new protection relay is able to not only significantly increase the speed of responses of conventional time grading protection scheme for single circuit breaker radial distribution feeders, but also remove faults from both ends of the protected lines section, therefore to achieve distribution automation

Research on order reduction of power system modeling for dynamic voltage stability analysis

Dynamic voltage stability analysis is mainly based on the time-domain solution of power system differential and algebraic equations. The modeling of each power element has a great influence on the correctness and complexity of stability analyzing. It is significant to model appropriately for simplifying calculation and drawing out principal contradiction. In this paper, the dynamical mechanism of voltage stability is summarized firstly. And based on the singular perturbation model taking into the fast and slow dynamics, this paper studies on how the quasi-steady-state model of power system approximates the dynamic of original system model. More, this paper employs the perturbation method and integral manifold theory as a tool for studying on the relationship of stability between the reduced-order system and original system. An important conclusion is reached that the power system quasi-steady-state model can be used for dynamic voltage stability analysis.

Study of Non-Unit Transient-Based Protection for HVDC Transmission Lines

It is difficult for existing HVDC line protections to distinguish internal fault from external fault rapidly and accurately, and the protective setting work encounters problems and difficulties. As a result, these protections have a low correct action rate. According to the feature of HVDC transmission system, this paper studies the characteristics of the natural boundary composed of the smoothing reactor and the DC filters. It is proved that this boundary has obvious differences in attenuation characteristics of different frequency components of fault transient signals. Consequently, a non-unit transient-based protection (NUTBP) is proposed. Wavelet multi-resolution signal decomposition technique is used to analyze the transient current caused by the faults. Extensive simulation results indicate that non-unit transient protection can clear all faults on the whole line quickly and credibly.

Study on security protection of transmission section to prevent cascading tripping and its key technologies

Cascading overload trip due to lack of transmission section protection is an important reason of large-scale blackout. This paper illustrates the meaning of transmission section and points out that the objective of transmission security protection is to maintain its integrality and transmission capacity, and to avoid cascading overload trip. In addition, the implement condition and key technology are discussed, which are online capture of transmission section, real-time prediction of cascading overload and real-time emergency control to avoid cascading trip. This paper has brought forward the primary scheme. Its validity is verified by the calculation result of CEPRI 36 test system and a province system.

Parameter identification of the transformer winding based on least-squares method

The principles of the equivalent circuit principle and the magnetic property theory are not affected by the inrush current and over-excitation, which enable protection to act rapidly and reliably and implement ideas different from differential protection. However, the leakage inductance and resistance of each winding are required as priori parameters. At present, there is no accurate measurement method for the transformer winding parameters. Therefore, it is very important for a method to accurately estimate the leakage inductance and resistance of the transformer. A new identification algorithm for transformer winding parameters is presented in this paper. Based on the electromagnetic relation between the primary and the secondary sides, the equation for transformer flux balance can be derived based on the transformer model. Through the elimination of the ratio of flux change with respect to time change from the equation, the discrete flux balance equations can be obtained through discrete process. Using the derivative of voltage and current as the input and output variables, the leakage inductances and resistances of every winding as the identification parameters, an identification model for transformer is built. Then parameters can be identified using this model. The least squares method based on the orthogonal decomposition is used to identify the winding parameters in this paper. A modified orthogonal method is adopted which is able to improve the numerical stability of classical Gram-Schmidt orthogonal method in the calculation. The requirement for the input signal is also discussed. The input signal should include sufficient number of frequencies with sufficient exciting time. If a system has n parameters to be identified, continuous excitation signal should contain at least n/2 different frequency components. Considering the actual operating conditions, this paper uses data from both sides of transformer when it is switched on with no-load and over-excitation to identify the parameters. The simulation results of electromagnetic transient program EMTP show that the parameters identified by the method proposed in this paper are very close to the true values with vary small errors. When data of transformer switching on with no-load is employed, the error of resistance is round about 1% and the error of inductance is less than 0.1%. When data of over-excitation is employed, the error of resistance is under 3% and the error of inductance is about 0.3 %. The characteristic of the multi-value and convergence of least squares method are greatly improved by the method proposed in this paper. In a certain range, more accurate identification parameters can be achieved by using the longer data length. The correctness of the identification results are also verified by simulation test. It has a great potential for the application to online identification.

Developments of transient and integrated protection for power system

The paper reviews the concept and development of the transient based protection and integrated protection for power systems. A number of new protection schemes with features of transient based and integrated protections are outlined. A new transient based integrated protection scheme for the protection of distribution system plant as well as distribution network as a whole using the transient polarity comparison technique is described. The scheme is based on the detection of fault generated transient current signals from all locations of the protected network. Comparison of the signal polarities obtained provides an indication of the actual faulted section. Like other transient based protection schemes, it is insensitive to the fault type, the fault inception angle, the fault path resistance and the line loading. In addition, it also has new features of integrated protection.