Modified Quasi-Steady State Model of DC System for Transient Stability Simulation under Asymmetric Faults

As using the classical quasi-steady state (QSS) model could not be able to accurately simulate the dynamic characteristics of DC transmission and its controlling systems in electromechanical transient stability simulation, when asymmetric fault occurs in AC system, a modified quasi-steady state model (MQSS) is proposed. The model firstly analyzes the calculation error induced by classical QSS model under asymmetric commutation voltage, which is mainly caused by the commutation voltage zero offset thus making inaccurate calculation of the average DC voltage and the inverter extinction advance angle. The new MQSS model calculates the average DC voltage according to the actual half-cycle voltage waveform on the DC terminal after fault occurrence, and the extinction advance angle is also derived accordingly, so as to avoid the negative effect of the asymmetric commutation voltage. Simulation experiments show that the new MQSS model proposed in this paper has higher simulation precision than the classical QSS model when asymmetric fault occurs in the AC system, by comparing both of them with the results of detailed electromagnetic transient (EMT) model of the DC transmission and its controlling system

Transient Characteristics Analysis of 500kV Parallel Circuit Breaker Based on Highly Coupled Split Reactor

With the continuous expansion of power system capacity, parallel high-voltage circuit breakers with a Highly Coupled Split Reactor (HCSR) have a potential application for limitation of high short-circuit current. However, as the parallel circuit breakers open at different time, the residual voltage of the split reactor on the post-open circuit breaker is higher and the stray capacitors of HCSR form high-order oscillating circuits, which may lead to serious transient recovery voltage (TRV). Therefore, it is necessary to analyze and simulate the transient characteristics of 500kV HCSR. Firstly, the equivalent model of HCSR circuit breakers is built in EMTP simulation plat-form, and its TRV generation is analyzed. Then, the TRV of parallel circuit breakers under different operating conditions and fault types is simulated and calculated. Finally, according to the statistical calculation results, the protection measure of 0.2uF shunt capacitance to limit rise rate of TRV is proposed

Subsynchronous control interaction analysis between PMSG-based offshore wind farm and SVGs

With the rapid development of wind energy, the subsynchronous oscillations (SSO) involved with wind conversion systems, has been the focus of academic concern. To analyse the subsynchronous control interaction (SSCI) issue of multi-converters (wind-power converter and widespread SVGs), the state matrix of a typical PMSGs-based offshore wind farm system including SVGs is constructed . It is proposed that SVGs in wind farm may cause SSCI issue by their uncoordinated control targets. Under certain conditions, the SSCI between SVGs forms the dominant oscillation mode, delivered with variation of the SSO frequency. By calculating the influence factors along with different converters, it can be concluded that unreasonable parameter configuration of converters and variations of operating conditions affect the SSCI characteristics. At last, time domain simulation is used to verify the SSCI mechanism and characteristics of the PMSG-based offshore wind farm and SVGs

Study on circuit breaker TRV issues of UHV high series compensation lines

Under the influence of series compensation (SC) capacitance and rated voltage rise, when ultra high voltage (UHV) high SC line occurs inner fault, the short-circuit current through the SC line is greater and the residual voltage across the SC is higher, which cause the electromagnetic transient process excited by high amplitude current and voltage to be more serious in the event of fault occurrence and removal. The security of circuit breaker (CB) equipment is threatened, which make it need further research on the characteristics and put forward some effective solutions. In this study, the characteristics of macroscopic statistical distribution of peak value via short-circuit current of transient recovery voltage (TRV) across CB fracture during switching after short-circuit current zero crossing for UHV high SC line are put forward, and also of the microscopic characterization parameter of waveform rise rate and peak value time. It shows that the TRV switching capability of existing UHV CBs can not cover all the fault scenarios of high SC line. Solutions including comprehensive comparison of TRV optimal suppression measures and increase of the UHV CB switching expected TRV test requirements are put forward, which provide feasible technical scheme for CBs reliable switching of UHV high SC line

Design of a Fatigue Detection System for High-Speed Trains Based on Driver Vigilance Using a Wireless Wearable EEG

The vigilance of the driver is important for railway safety, despite not being included in the safety management system (SMS) for high-speed train safety. In this paper, a novel fatigue detection system for high-speed train safety based on monitoring train driver vigilance using a wireless wearable electroencephalograph (EEG) is presented. This system is designed to detect whether the driver is drowsiness. The proposed system consists of three main parts: (1) a wireless wearable EEG collection; (2) train driver vigilance detection; and (3) early warning device for train driver. In the first part, an 8-channel wireless wearable brain-computer interface (BCI) device acquires the locomotive driver’s brain EEG signal comfortably under high-speed train-driving conditions. The recorded data are transmitted to a personal computer (PC) via Bluetooth. In the second step, a support vector machine (SVM) classification algorithm is implemented to determine the vigilance level using the Fast Fourier transform (FFT) to extract the EEG power spectrum density (PSD). In addition, an early warning device begins to work if fatigue is detected. The simulation and test results demonstrate the feasibility of the proposed fatigue detection system for high-speed train safety