Failure of vulnerable lines in the power system often results in tidal shifts, and triggering chain failures and their corresponding transmission sections are concentrated manifestations of the weak links in the power system. It is very important to identify the vulnerable lines and search the transmission section to prevent the chain faults as well as to analyze the stability of the power system. Aiming at the problems of inaccurate search of vulnerable lines, difficulties adapting to the complex and changing power system as well as wrong selection and omission of transmission section search in the existing references, this paper proposes an algorithm for searching vulnerable lines and their key transmission sections based on the graph theory and PMU (phasor measurement unit) data. First, the method combines with the graph theory and PMU data to construct the grid topology map. Second, the comprehensive indicators for screening vulnerable lines are proposed by fully considering the network topology and line capacity, which combines with power exchange efficiency and energy fluctuation probability. Third, the distance matrix in the Floyd algorithm is transformed into a unit group that can store more elements, which reduces the traversal times of the algorithm and improves computational efficiency. The fast localization of transmission cross sections associated with vulnerable lines is realized. Finally, the critical transmission cross sections are screened according to the line outage distribution factor and line safety margin. The IEEE 39-bus system is selected for simulation experiments, and the simulation results show that the key transmission section search method proposed in this paper can better adapt to the variable power grid and is faster and more accurate than the other common method.
As more and more DGs plugging into low voltage side of the distribution network, the traditional distribution network is transformed from single-supply radial network to multi source network, which makes the overcurrent protection cannot be reliably realized by traditional protection devices and theories. Based on the application of synchronous phasor measurement technology in the smart distribution network, this paper analyzes the characteristics of the current phase difference in the sections with loads or branch lines quantitatively. Based on the above, this paper then proposes a novel auto-adaptive fault location and monitoring method based on section load estimation. At the same time, this paper analyzes the impact of different load types on the proposed fault location method. Verification of the proposed method has been carried out by simulating in the PSCAD, and the simulation results indicate that the short-circuit faults can be located and recognized accurately with fast speed and self-adaption.
High impedance arc faults (HIAFs) happening in the medium-voltage distribution system may result in damages to devices and human security. However, great difficulties exist in identifying these faults due to the much weaker features and the varieties when grounded with different surfaces. This paper presents an integrated algorithm to detect the HIAFs with high-resolution waveform data provided by distribution-level PMUs deployed in the system. An improved arc model is proposed, which can continuously imitate the randomness and intermittence during the "unstable arcing period" of arc faults. The integrated algorithm consists of two branches. First, the variations of HIAFs during unstable arcing period are identified with the unified harmonic energy and global randomness index, which can unify the scales of harmonic content in different fault situations and enlarge the disparities from non-fault conditions. Then, the waveform distortions of HIAFs during the stable arcing period are identified with discrete wavelet transform to extract the detailed distribution characteristics. The reliability and security of the proposed algorithm are verified with numerical simulations and field tests in a 10-kV distribution system.
Sudden loss of bulk power generation will result in significant power shortage and power flow redistribution, which may lead to insecurity and/or stability problems. Under this condition, load shedding (LS) and corrective line switching (CLS) can be used to guarantee a reliable electricity supply. However, at present, the above two procedures are implemented separately, which may deteriorate each other and cause unnecessary load loss. To address this issue, a coordination optimization method is proposed to coordinate event-driven LS and CLS for enhancing power system security and stability as well as reducing LS amount simultaneously. A two-loop integrated algorithm is designed to solve the constrained optimization problem, which takes the transient frequency/voltage deviation and overload capacity of the transmission lines as constraints. In the inner loop, iterative optimization of the LS for frequency/voltage security is achieved based on linearized sensitivity analysis, and then step-by-step summation is employed to get the LS amount for alleviating overload. Neighbor search is used in the outer loop to coordinate event-driven LS and CLS so as to optimize the total LS amount. The effectiveness of the proposed method is validated in a modified IEEE 39 bus test system and an industrial power system. The results show that the proposed scheme can decrease the LS amount without improve the transient security while maintaining the transient security and alleviating overload.
With plenty distributed generations accessing to the distribution network, dynamic behavior of the system becomes more complex. However, most of the current condition monitoring products are concentrated on the high voltage grid. It's necessary to extend condition monitoring to low voltage distribution network and provide a new decision support systems for grid operation. This paper presents a panoramic synchronous measurement system (PSMS), which is based on the cloud computing. This system integrates the wide-area measurement system (WAMS) and fault recorder system in high-voltage grid with the wide-area measurement system light (WAMS Light) in low-voltage grid. It constructs a four-tier structure in main station to achieve panoramic monitoring, which covers all voltage level. This method makes full use of the existing data sources and avoids repeated investment of monitoring network rebuilding. For the three kinds of measurement data different in the coding, type and format, this paper describes the common data character with big data perspective to integrate heterogeneous data in HBase. Hadoop is introduced to control the measurements migration, cleaning, integration and cloud computing, facilitating the dispatchers comprehensively capture the actual operation behavior of the monitored power grid.
With the generalization and application of PMUs, the approach of the measurement and calculation for the electrical parameters in power grid are greatly enriched. But at present, PMU can only calculate the fundamental phasor and the utilization ratio of hardware resources is low. Firstly, based on the calculation principle of PMU for fundamental phasor calculation, the algorithm of PMU to calculate harmonic phasor is proposed. Secondly, the accuracy of harmonic phasor calculated by PMU and harmonic phasor calculated by conventional Fast Fourier Transform (FFT) is compared when the signal frequency deviates from the rated frequency. Thirdly, the harmonic phasors calculated by PMU and conventional FFT are used for harmonic contribution determination (HCD). The feasibility of harmonic phasor calculated by PMU on improving the accuracy of HCD is analyzed based on the case study results. Finally, the effectiveness of the proposed method is verified based on 18-bus distribution system. The case-study results show that the accuracy of the proposed method is good. The harmonic phasor data calculated by PMU is of great value for improving the accuracy of HCD.
Low-frequency oscillation suppression of the interconnected power grid is an important factor for the stable operation of the power system. In this paper, the AC-DC interconnected power system is represented as the switched Hamilton system based on the centre of inertia (COI) equivalent method. The Hamilton energy function of the system is constructed from the viewpoint of the oscillation energy of the interconnected power system, which is then used as a uniform Lyapunov function to study the stabilization problem of the system. Then the high voltage direct current (HVDC) supplementary damping controller is designed aiming to reduce the oscillation energy thus the suppression of the oscillation is attained. The proposed control design procedure is fully based on nonlinear theory and can be widely used for practical power system with changing operation conditions. The feasibility of the proposed controller in the practical power system is discussed based on wide-area measurement system (WAMS). The simulation results of the EPRI 7 nodes system verify the correctness and effectiveness of the proposed method. DOI: http://dx.doi.org/10.5755/j01.eee.20.4.4230
Electric vehicles (EVs) are new power loads of power systems. It is important to model the charging process of EVs in power system numerical simulation. This paper proposes a methodology for modeling of EV loads applicable to power flow calculation and other quasi-steady state analysis. The numerical methodology of EV load modeling is expounded from the DC and the AC side of charging EVs. In the DC side, the constant current and the constant voltage charging processes are considered. In the AC side, the changes of the charging efficiency and power factor versus the AC frequency and voltage are analyzed. Based on the current EV market status and the development trends, four types of EV load models are calculated using this methodology. The EV load modeling methodology considers EV quantities, initial state-of-charge distributions, load change processes during charging and the effect of grid side parameters.
With the introduction of the "Dual Carbon" policy, the proportion of electric power in the final energy consumption will continue to increase, and the construction of the power transmission grid will also usher in new development. Equipment parameters are the foundation of grid research and the key to ensuring the safe and stable operation of the system. In this article, by consulting national standards, design specifications, and referring to typical projects, we have formed a database of typical design solutions for the power transmission grid and a dataset of typical component parameters for the power transmission grid. By processing and analyzing actual data from a large-scale power grid, we provide the distribution patterns of parameters for transmission lines and transformers respectively. With reference to the distribution patterns, parameter verification rules are formulated and implemented using the C language algorithm. The verification of parameters for 500kV and 220kV AC transmission lines is conducted based on the verification rules, and the results demonstrate the reasonability of the verification rules and the typicity of the equipment parameters in the dataset.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
'/%3e%3cpath fill='%23fff' d='m8.751-17.959 10.11 11.373L3.997-9.844l13.94-6.1-7.692 13.129z'/%3e%3c/svg%3e)