With the development of renewable electric power generation and ultra-high voltage direct current (UHVDC) transmission, the transient overvoltage in the sending end electric power system with UHVDC occurs, but it is lack of quantitative transient voltage assessment index (TVAI) to assess the overvoltage. To deal with the above problems, this paper proposes a new quantitative transient voltage assessment index considering overvoltage and voltage dip in the sending end electric power system with UHVDC, and applies it to analyze different influencing factors of overvoltage and determine the dynamic reactive power compensation capacity. In detail, first, according to the principle of the transient voltage assessment index considering voltage dip and the overvoltage assessment index for the distribution network, a new transient voltage assessment index considering transient overvoltage in the sending end electric power system with UHVDC is proposed with the approximated step function. Then, based on the requirements of the system with UHVDC, the parameters of the proposed transient voltage assessment index are determined. Furthermore, with the absolute and relative sensitivity, the impact of the parameters of voltage dependent current order limiter and current control amplifier on the transient overvoltage is analyzed and compared quantitatively. Finally, the impact of reactive power compensation equipment, such as synchronous condenser, static var compensator, and static var generator, on the transient overvoltage of the system with UHVDC is compared quantitatively, and the reactive compensation capacity needed to maintain transient voltage security and stability is estimated. The two applications show the effectiveness and advantages of the proposed index in the sending end electric power system with UHVDC.

This study proposes a new voltage stability index based on the voltage equation of transmission lines. The proposed index is obtained by using the characteristic that the sensitivity of voltage to power at the voltage collapse point tends to be infinite. Furthermore, the proposed index is also validated in the case of inverse power flow, and the condition of monotonicity is discussed. Simulation results in a single branch system, a 10‐bus system and a regional power system verify the effectiveness of the proposed on‐line voltage index. The simulation results also show that the proposed index is better than the on‐line branch voltage stability index and is more promising for use in industry. The proposed index can be readily calculated from the measurements at the two terminals of the branch, which can be obtained with PMUs. Hence it is suitable for online applications. Finally, issues related to the practical application of the proposed index are discussed.

For the power system interconnected with the large-scale offshore wind power through VSC-HVDC, such as SZ power grid, it may be engaged with transient frequency stability and lack of related control due to the randomness, fluctuation and intermittence of the wind. This paper proposes a transient frequency control strategy for the power system interconnected with offshore wind power through VSC-HVDC based on sensitivity. Firstly, the structure of SZ power grid and the calculation method of transient frequency stability index are introduced, and the transient frequency problems existing in SZ power grid are explored. Secondly, the mathematical formulation for the transient frequency control is described, including the objective function and the constraints. Furthermore, a transient frequency emergency control strategy based on special sequence and the sensitivities is proposed, which includes thermal units regulation, wind power regulation, DC modulation and load shedding. Finally, the effectiveness of the proposed control strategy is verified by simulation in SZ power grid.

Currently, a large amount of defect data in relay protection devices (RPDs) is accumulated in operation. However, the defect data dependence analysis is absence and thus it could not meet the demand for further improving the management and operation RPDs. Based on 7-years defect data of RPDs in SGCC, this paper discovers the association rules (ARs) of defect data based on the Apriori algorithm. In detail, the ARs among different categories of PRDs, such as defect parts and defect causes are discovered and analyzed. Furthermore, the family characteristics of defects are illustrated, with the defect data of RPDs from different manufacturers. The analysis results show that the Apriori method can effectively reveal the hidden information in the defect data, such as the ARs between the vulnerable parts of RPDs, defect causes and other factors.

Accurate transmission line parameters are the basis of power system calculations. The measured phasor measurement unit (PMU) phase angle data at both ends of a line may contain large errors caused by synchronization problems, which can seriously affect the accuracy of parameter identification. This paper proposes a robust PMU-based method for calculating transmission line parameters from PMU data at both ends of a line in such a way that a synchronization error between the ends does not degrade the results. Specifically, a π-equivalent model for the transmission line is established, and a least square objective function with nonlinear equations for positive parameter identification is derived. Furthermore, to reduce the impact of noise and biased data, median estimation is used to obtain the final result. Finally, a simulation shows the effectiveness and robustness of the proposed method, and its practicality is demonstrated in a case study using measured PMU data.