Electromagnetic relay is a widely used apparatus which usually works in a magnetic disturbance environment. To evaluate its electromagnetic compatibility (EMC) in a static magnetic field, dynamic characteristics of a ...Electromagnetic relay is a widely used apparatus which usually works in a magnetic disturbance environment. To evaluate its electromagnetic compatibility (EMC) in a static magnetic field, dynamic characteristics of a clapper relay in a uniform static magnetic field situation based on the finite element method (FEM) is studied. Influences of the magnetic field on dynamic parameters (delay time, pick-up time, end pressure, and final velocity) as well as a situation in which the relay cannot function normally are analyzed. Simulation reveals that the external magnetic field which weakens the relay’s air-gap field has a greater influence on the relay’s dynamic parameters than the one strengthening the field. The validity of the simulation is verified by measured results of coil current and armature displacement.展开更多
Determining the fault location using conventional impedance based distance relay in the presence of FACTS controllers is a challenging task in a transmission line. A new distance protection method is developed to loca...Determining the fault location using conventional impedance based distance relay in the presence of FACTS controllers is a challenging task in a transmission line. A new distance protection method is developed to locate the fault in a transmission line compensated with STATCOM with simple calculations. The proposed protection method considers the STATCOM injected/absorbed current to correct the fault loop apparent impedance and accordingly calculates the actual distance to the fault location. The comprehensive equations needed for apparent impedance calculation are also outlined and the performance is evaluated and tested with a typical 400 KV transmission system for different fault types and locations using MATLAB/SIMULINK software. The evaluation results indicate that the new protection method effectively estimates the exact fault location by mitigating the impact of STATCOM on distance relay performance with error less than 0.3%.展开更多
The coordination correctness of Nuclear power plant current transformer (CT)/ voltage transformer (PT) polarity and relay protection is often verified through the dynamic test on the unit no load / load operating cond...The coordination correctness of Nuclear power plant current transformer (CT)/ voltage transformer (PT) polarity and relay protection is often verified through the dynamic test on the unit no load / load operating conditions. This paper proposes a test method to prevent and circumvent the failure of the dynamic test abnormality caused by the static power test before the plant power is applied and the whole group is started. Reduce the dynamic test workload and test difficulty, to ensure that the dynamic test safety risk control and control in the state.展开更多
文摘车载边缘计算(vehicular edge computing,VEC)是一种可实现车联网低时延和高可靠性的关键技术。VEC可解决车载终端计算能力不足的问题,同时可减少车联网通信服务时延,避免路边停泊车辆自身大量空闲资源浪费。提出基于停泊车辆中继的车载任务卸载方案,通过合理部署边缘服务器和引入协作中继技术,可将车联网通信过程中的时延降低至毫秒级。仿真结果表明,与传统的车与基础设施(vehicle to infrastructure,V2I)卸载方案相比,基于停泊车辆中继的车载任务卸载方案可将通信时延降低20%。
基金Project (No. 513230502) supported by the PLA General ArmamentDepartment of China
文摘Electromagnetic relay is a widely used apparatus which usually works in a magnetic disturbance environment. To evaluate its electromagnetic compatibility (EMC) in a static magnetic field, dynamic characteristics of a clapper relay in a uniform static magnetic field situation based on the finite element method (FEM) is studied. Influences of the magnetic field on dynamic parameters (delay time, pick-up time, end pressure, and final velocity) as well as a situation in which the relay cannot function normally are analyzed. Simulation reveals that the external magnetic field which weakens the relay’s air-gap field has a greater influence on the relay’s dynamic parameters than the one strengthening the field. The validity of the simulation is verified by measured results of coil current and armature displacement.
文摘Determining the fault location using conventional impedance based distance relay in the presence of FACTS controllers is a challenging task in a transmission line. A new distance protection method is developed to locate the fault in a transmission line compensated with STATCOM with simple calculations. The proposed protection method considers the STATCOM injected/absorbed current to correct the fault loop apparent impedance and accordingly calculates the actual distance to the fault location. The comprehensive equations needed for apparent impedance calculation are also outlined and the performance is evaluated and tested with a typical 400 KV transmission system for different fault types and locations using MATLAB/SIMULINK software. The evaluation results indicate that the new protection method effectively estimates the exact fault location by mitigating the impact of STATCOM on distance relay performance with error less than 0.3%.
文摘The coordination correctness of Nuclear power plant current transformer (CT)/ voltage transformer (PT) polarity and relay protection is often verified through the dynamic test on the unit no load / load operating conditions. This paper proposes a test method to prevent and circumvent the failure of the dynamic test abnormality caused by the static power test before the plant power is applied and the whole group is started. Reduce the dynamic test workload and test difficulty, to ensure that the dynamic test safety risk control and control in the state.
