Search

Extra-high (EHV) transmission system has the characteristics of high voltage and large capacity, and a high amplitude current will be generated through the grounding line and ground net when failure occurs. Step voltage caused by the diffusion of fault current in soil is an important parameter affecting the normal operation of the system. The calculation and analysis of the step voltage in IEEE Std 80-2000 standard is rough, unable to reflect the soil surface potential distribution in substation comprehensively. This paper present an algorithm combined transmission line theorem and finite element analysis to calculate the electric potential distribution accurately, getting the attenuation law of surface potential and the step voltage. Analysis shows that the soil surface electric potential is well-distributed in normal operation and the step voltage is very small, only a dozen volt; The potential value can achieve kilovolt during short trouble and there will be a great attenuation within one meter; Soil resistivity, earth current amplitude and buried depth of ground net are the important factors influencing the surface potential distribution and step voltage.

The insulation characteristic of high voltage circuit breaker in cold regions is the basis for the design of high voltage circuit breaker. In this paper, several gas of physical and insulated properties can be used in cold region circuit breaker are compares, CF4 gas was fed to use gas for cold region circuit breaker is obtained. Breakdown experiment of CF4 under typical electrodes was investigated, and the insulation performance of CF4 under short gap is obtained. The necessary basic data of CF4 mixed gas circuit breaker insulation and interruption performance research for cold region are provided.

Vacuum circuit breakers switch off shunt reactors, when the low voltage ride-through (LVRT) experiments are performed in Photo-voltaic (PV) system. Transient over-voltage is occurred and gotten a high amplitude in the experiments. It would cause external insulation breakdown of reactor and equipment damage. Base on circuit theory, this paper focused on factors which impacted on the transient over-voltage in the 35kV PV-LVRT experimental system. And then according to 35kV LVRT experimental line, a simulation model of experimental system was established in ATP/EMTP. The simulation results indicated that the closure value of vacuum circuit breaker the size of invested short-circuit reactance and the size of shunt capacitor were major influencing factors on the transient over-voltage caused by vacuum circuit breaker operation. A 0.1 μF shunt capacitor and a 100Ω shunt resistor could effectively reduce the peak value of transient over-voltage what were set to test point in the experiment.