Wang Feiming

Study on the Mathematical Model of Dielectric Recovery Characteristics in High Voltage SF6 Circuit Breaker

According to the stream theory, this paper proposes a mathematical model of the dielectric recovery characteristic based on the two-temperature ionization equilibrium equation. Taking the dynamic variation of charged particles ionization and attachment into account, this model can be used in collaboration with the Coulomb collision model, which gives the relationship of the heavy particle temperature and electron temperature to calculate the electron density and temperature under different pressure and electric field conditions, so as to deliver the breakdown electric field strength under different pressure conditions. Meanwhile an experiment loop of the circuit breaker has been built to measure the breakdown voltage. It is shown that calculated results are in conformity with experiment results on the whole while results based on the stream criterion are larger than experiment results. This indicates that the mathematical model proposed here is more accurate for calculating the dielectric recovery characteristic, it is derived from the stream model with some improvement and refinement and has great significance for increasing the simulation accuracy of circuit breakers interruption characteristic.

Grounding system circulation calculation of ultra-high voltage switching substation

For the phenomena of UHV system high voltage and large capacity, circulating current in the shell and grounding network is relatively large. Under steady-state operation, shell will product a large loss of circulating current. Combined with the 1100 kV HGIS substations, according to the basic principles of electromagnetic transformers, GIS / HGIS shell equivalent circuit model is created and model parameters are determined. The π-type equivalent is used to show grounding element and the use of numerical methods for the electrical grounding system parameters. Analysis showed that circulating current of the main mesh is controlled to less than 20A and circulating current of the sub-mesh is controlled to less than 700A by using double level grounding network. However, the short-wire current is large. Further analysis, there is effect that application of deep vertical grounding electrode and short-wire reduce the circulating current of grounding network, and the best design have been given. Finally, the circulating current value and temperature rise of each part will be given.