Transitional Recovery Voltages at Capacitive Currents Switching-off by Vacuum and SF6 Circuit-Breakers

Results of calculation the recovery voltages conditioned by capacitive currents switching-off by high voltage vacuum and auto-compression （SF6） circuit-breakers are presented in the article. The purpose of research was evaluating the maximum values of recovery voltages and also studying the dependence of recovery voltages on some influencing factors, especially on type of circuit-breaker presented in numerical models with its dielectric strength restoration law, chopping current and operation time. The research was carried out with using computer simulation.

The Voltage Distribution Characteristics of a Hybrid Circuit Breaker During High Current Interruption

Hybrid circuit breaker （HCB） technology based on a vacuum interrupter and a SF6 interrupter in series has become a new research direction because of the low-carbon requirements for high voltage switches. The vacuum interrupter has an excellent ability to deal with the steep rising part of the transient recovery voltage （TRV）, while the SF6 interrupter can withstand the peak part of the voltage easily. An HCB can take advantage of the interrupters in the current interruption process. In this study, an HCB model based on the vacuum ion diffusion equations, ion density equation, and modified Cassie-Mayr arc equation is explored. A simulation platform is constructed by using a set of software called the alternative transient program （ATP）. An HCB prototype is also designed, and the short circuit current is interrupted by the HCB under different action sequences of contacts. The voltage distribution of the HCB is analyzed through simulations and tests. The results demonstrate that if the vacuum interrupter withstands the initial TRV and interrupts the post-arc current first, then the recovery speed of the dielectric strength of the SF6 interrupter will be fast. The voltage distribution between two interrupters is determined by their post-arc resistance, which happens after current-zero, and subsequently, it is determined by the capacitive impedance after the post-arc current decays to zero.

An Adaptive Data-driven Method Based on Fuzzy Logic for Determining Power System Voltage Status

This paper proposes an adaptive method based on fuzzy logic that utilizes data from phasor measurement units(PMUs) to assess and classify generating-side voltage trajectories. The voltage variable and its associated derivatives are used as the input variables of a fuzzy-logic block. In addition, the voltage trajectory is compared with the pre-selected pilot-bus voltage to make a reliable decision about the voltage operational state. Different types of short-term voltage dynamics are considered in the proposed method. The fuzzy membership functions are determined using a systematic method that considers the current situation of the voltage trajectory. Finally, the voltage status is categorized into four classes to determine appropriate remedial actions. The proposed method is validated on a IEEE 73-bus power system in a MATLAB environment.

Study on TRV of circuit breaker in two substation operational ways and its countermeasure

To verify a vacuum breaker's feasibility,when a transformer substation chooses a vacuum circuit breaker,it takes two different actual operational ways to cut off a transformer.This paper,using the power system computer aided design/electro magnetic transient in DC system(PSCAD/EMTDC)software,simulates the substation system and studies transient recovery voltage(TRV)caused by the two different ways which can cut off a with load transformer or a no-load transformer.Simulation and calculation results show that TRV indexes of the first way are much higher than that of the second one,and their TRV indexes are both in a permissible range.The breaker is proved to be available.Besides,this paper proves that paralleling resistance has a good effect when the indexes exceed the standard.The resistance value depends on specific circumstances.

A Repetitive Nanosecond Pulse Source for Generation of Large Volume Streamer Discharge

Using a unipolar pulse with the rise time and the pulse duration in the order of microsecond as the primary pulse, a nanosecond pulse with the repetitive frequency of several kilohertz is generated by a spark gap switch. By varying both the inter-pulse duration and the pulse frequency, the voltage recovery rate of the spark gap switch is investigated at different working conditions such as the gas pressure, the gas composition as well as the bias voltage. The results reveal that either increase in gas pressure or addition of SF6 to the air can increase the voltage recovery rate. The effect of gas composition on the voltage recovery rate is discussed based on the transferring and distribution of the residual space charges. The repetitive nanosecond pulse source is also applied to the generation of large volume, and the discharge currents are measured to investigate the effect of pulse repetition rate on the large volume streamer discharge.

Dynamic Frequency Support and DC Voltage Regulation Approach for VSC-MTDC Systems

When an additional frequency control is implemented in the voltage source converter-based multi-terminal high voltage direct current(VSC-MTDC)system,the DC grid is capable of responding to a frequency disturbance in the AC system.However,the original additional frequency control may cause the DC voltage to exceed the limit when providing power for a severe frequency disturbance,threatening the security of the DC system.A novel dynamic additional frequency control strategy for the VSC-MTDC system is developed based on the relationship between the DC voltage and the frequency droop coefficient.A dynamic frequency droop coefficient is designed to adaptively adjust the support power of the DC grid,balancing the frequency regulation of the disturbed AC system and the voltage stability of the DC grid.A DC voltage recovery method based on multi-converter cooperation is proposed to cope with the DC voltage deviation caused by the additional frequency control.Simulations validate the advantages and satisfactory performance of the proposed method during power disturbances with different severities and for the process of DC voltage recovery.

Dynamic reactive power planning method for CSP-PV hybrid power generation system

Aiming at the faults of some weak nodes in the concentrated solar power-photovoltaic(CSP-PV)hybrid power generation system,it is impossible to restore the transient voltage only relying on the reactive power regulation capability of the system itself.We propose a dynamic reactive power planning method suitable for CSP-PV hybrid power generation system.The method determines the installation node of the dynamic reactive power compensation device and its compensation capacity based on the reactive power adjustment capability of the system itself.The critical fault node is determined by the transient voltage stability recovery index,and the weak node of the system is initially determined.Based on this,the sensitivity index is used to determine the installation node of the dynamic reactive power compensation device.Dynamic reactive power planning optimization model is established with the lowest investment cost of dynamic reactive power compensation device and the improvement of system transient voltage stability.Furthermore,the component of the reactive power compensation node is optimized by particle swarm optimization based on differential evolution(DE-PSO).The simulation results of the example system show that compared with the dynamic position compensation device installation location optimization method,the proposed method can improve the transient voltage stability of the system under the same reactive power compensation cost.