Operation Risk Assessment On Power Grid In Ice Storm And Network Protection

In early2008, catastrophic ice storm attacks southern china, and pose a greatthreat for the safe and stable operation of power grids in the affected areas. Extremeweather ice storm could make a lot of damage to the power grid elements in a shorttime, causing power blackouts and paralysis. For this, it is necessary to combinewith stress characteristics of transmission lines during the ice disaster, whenquantitatively considering the grid operation reliability.In this paper, the calculation method of power line failure probability in thecombined effects of icing and wind is given. This method of line ice thicknesscalculation obtains weather information form meteorological station by the weightedaverage method. From the view of mechanics, the calculation of wind-ice force isgiven to analyzes the influence of combined effect of wind and ice on thetransmission line. the failure probability of power lines is calculated by using theexponential model which reflects the characteristics of the metal bearing limits.Line failure model is etablish by considering the effect both ice storm and linepower flow. Assess the grid risk in ice storm base on fault tree. Load loss, failureprobability and power flow are calculated. Study the grid failure state, to get the riskof loss load and risk of exceeding line flow limit when power system occurscascading failures. The risk of the system is sum of risk of loss load and risk ofexceeding line flow limit. Fault set could be established by risk of system. Theresults of simulation example using historical weather data from meteorologicalstation show that this method can provide line fault probability and provide relevantinformation for power grid risk assessment.The network topology and grid operation mode could change frequently,because alot of power line broken during the ice storm, result on inceausing of theprobability of traditional relay malfunction and tripping. For this, this paperproposes a network differential protection method base on generalized node theory.Network differential protection model is proposed based on the concept ofgeneralized Kirchhoff’s current law. The set of the operating current of this methodcould ignore the influence of changes of operating mode, expressly in extremeweather during which the grid topological structure and operation mode changesfrequently. Considering the the tripping of protection devices and changes of gridtopological structure and measuring points in grid, generalized node differentialbackup protection algorithm is proposed. Using differential protection networkprotection as backup protection can quickly remove the fault line selectively. It cannarrow the scope of failure and educe the risk of cascading failures. This research is supported by State Grid Corporation of China (SGCC)(NO.SGCC-MPLG-023) and National High Technology Research and Development ofChina (863Program)(NO.2011AA05A105).