The Arc Model in SiO_2 Current-limiting Fuse

An arc model in SiO2 current-limiting fuse has been put forward. Through taking into account the comprehensive effects such as: fundamental action process among particles of arc column, geometrical and external circuit characteristics of arc column, physical procedure in arc column and in cathode and anode, and power equilibrium in arc column plasma et al., parameters such as the temperature, length, volumn, pressure, arc voltage, arc current et al. in the arc column can be obtained by the model. In view of the serious nonlinearity and huge difference among parameters in the equation set of the model, via analysis on these equations, two solution methods for the equations of the model have been presented with a basic accordance between calculated results and test results.

Current-limiting Characteristics of a Modified Flux-coupling Type Superconducting Fault Current Limiter and Its Effects on the Transient Stability of a Multi-machine Power System

A modified flux-coupling type superconducting fault current limiter(SFCL)is proposed here for suppressing fault currents.The modified SFCL consists of a coupling transformer,an yttrium barium copper oxide(YBCO)pancake coil,and a controlled switch.By flexibly adjusting the controlled switch’s contact states based on the system operational conditions,the coupling transformer’s primary inductance as well as the YBCO coil’s normal-state resistance are incorporated into the main system for current limitation.Because the modified SFCL has the advantages of resistive and inductive SFCLs,it may improve the power system’s transient behavior.Hence,the SFCL’s effect on the transient stability of a multi-machine power system was also theoretically investigated.Further,simulations were conducted for accessing the SFCL’s performance characteristics under different fault conditions.The results show that using the proposed SFCL can effectively restrain the increased fault current and improve the bus voltage sag;meanwhile,the imitated multi-machine system’s power-angle oscillation can be obviously reduced.

Studies on the active SISFCL and its impact on the distance protection of the EHV transmission line

The active saturated iron-core superconductive fault current limiter(SISFCL)is a good choice to decrease fault current.This paper introduced the principles and impedance characteristic of the active SISFCL.Then,it shows the current-limiting effects of the SISFCL.Besides,the impact of the active SISFCL on the distance protection of the EHV transmission line is evaluated.Based on that,the coordination scheme of the distance protections is proposed.A 500 kV double-circuit transmission system with SISFCLs is simulated by Electro-Magnetic Transients Program including DC(EMTDC).Simulation tests demonstrate the correctness and validity of theoretical analyses.

Coordinated Suppression Method of Fault Current for DC Grid with Novel Dissipative Resistors Topology

A DC grid based on half-bridge modular multilevel converters(HB-MMC)is a feasible means to realize the friendly grid connection of renewable energy.To solve problems such as the high cost and technical difficulty of DC circuit breakers(DCCB),a coordinated control method for fault current suppression of DC grid connecting wind power is proposed.The key influencing factors of DC fault current are revealed by fault characteristics analysis,and an adaptive current-limiting control method for MMC is proposed,whose parameter selection principles are designed to ensure the safe operation of equipment while achieving effective suppression of fault current.In addition,a novel configuration method of dissipative resistors with the current-limiting function is proposed,which can solve the problem of surplus power in the DC grid and reduce the current stress of converter valves.Based on this,a coordination scheme of dissipative resistors,the adaptive current-limiting control method,and DCCBs are proposed to block fault current,effectively reducing the manufacturing difficulty and cost of DCCB.Finally,a four-terminal DC grid simulation model is built based on the RTLAB OP5600 real-time digital simulation platform,and the effectiveness and feasibility of the proposed methods are verified.