Research On Power System Modeling Suitable For Relay Protection Setting Calculation

Protection relay setting and coordination is an important and basic work which determines the relay setting and guarantees the safe operation of power grids. Setting calculation needs a large number of fault calculations, so it requires that power system model used in setting calculation, on the one hand, should be simple to reduce computation cost of fault calculation, on the other hand, can reflect the fault characteristic of grid and ensure the accuracy of setting calculation. With the rapid development of grid, the features of grid are presented as continuous enlarging scale, increasing structural complexity and power transmission, rapid expanding electrified railway capacity, which has become a new challenge to power system model suitable for setting calculation. Therefore, the analysis and research have been done in this paper on generator model, load model and traction transformer model. The main contents are as follows:The characteristics of the existing dynamic generator models and their relationships have been analyzed. This paper proposes a staged generator model suitable for backup protection which uses the typical time of relay protection as demarcation point. By the studies of the characteristics of generator at the typical time point, the staged generator model suitable for backup protection can be formed from the static generator model in this period. Compared to the fifth order model of generator, it has higher practicability in relay protection setting; Compared to the existing model, it has higher simulated accuracy of short-circuit current at the typical time point and solves the problem that the existing model is not very accurate in backup protection setting.With the analysis on features of protection relay setting and coordination, constant resistance model suitable for setting calculation is determined. The method of selecting load suitable for setting calculation is proposed in this paper. Electrical distance and the variety coefficient of current is used to select load which has stronger effect on grid. The method can not only ensure the result of fault calculation precision, but also reduce the time of short circuit current calculation. Besides, based on compensation method, the fast method of short circuit current calculation considering load is proposed, the original network matrix doesn't need to be modified and the time of short circuit current calculation will be reduced by the method.Based on the basic principle of transformer, connection types of traction transformers and their features are introduced, including single phase traction transformer, V/V connection traction transformer, YNd11 connection traction transformer, Scott connection traction transformer and impedance matching balance traction transformer. All kinds of fault equivalent models of each type are concluded in this paper which provide theoretical support for setting calculation of grid including traction transformers.