The Influence And Mechanism Research On Power Grid Transient Stability Of The Distribution Network Model

While the scale of power system in China is continuously extending, the distribution network of the data used in current power system simulation calculation are often simplified to an equivalent load connected to the main network. But with the rapid development of new energy, the number of power merged into distribution network is growing, which makes the originally radiated power distribution network evolved into a network in which power source and users can connect each other. The negative load supplied from the distribution network load side to the main power system appears in more and more areas. The loads with different power flow directions make the distribution network model now used in the power system simulation can't meet the actual needs, so it's nessesary to improve the construction methods for data now used in power system simulation calculation, and establish a new distribution network model with more actuality and accuracy.In order to study the influence of the negative load on the power grid transient stability simulation results, firstly, the influence of the negative load which supplies power to the grid on the power grid transient stability was systematically analyzed in a 3regional system, and then the mechanism of that influence was described. In a provincial area power grid as engineering background, the validity of the conclusions regularity was examined. Based on extensive statistical analysis of simulation results, the regional provided load percentage Xi was defined. The paper pointed out that influence of the negative load on power grid transient stability calculation results can not be ignored in the region whose Xi is more than 16%, and in that region the distribution network model which has a higher degree of accuracy should be established. Thus a construction method of power system simulation calculation data considering the distribution network and the power of it was proposed. In this method, the region of power grid was divided according to their Xi; on one hand, the region which Xi isn't more than 16% can still use the current calculation data, on the other hand, in the area which Xi is more than 16%, the part of main grid still use the current calculation data but the part of distribution network should use the distribution network model considering the influence of 110 k V and below distributed power on power grid. This method extends the calculation data constructed in detail to the low voltage network which has much distributed power so as to improve the accuracy of the distribution network calculation data, and it avoids the transient stabilitycalculation error brought by the large number of negative load in PSASP, so the simulation results are much closer to the actual behavior of the power grid.By using this method and taking a province grid as engineering background, the effects of the power system simulation calculation data using different models of its distribution network on transient stability level were systematically compared. In order to deeply reveal the influence of the distribution network model on transient stability of the power grid, and based on the correlation in power system between the proportion of power receiving and transient stability,the laws of that correlation were compared and analysed when power grid using the current distrubution network model or the proposed. The results show that transient stability level will be improved after adding the distribution network model taking distributed power into account in the power grid simulation calculation data. Thus it's recommended that the function of supporting dynamic reactive power provided by the power in the region which Xi is more than 16% should be considered and the distribution network model currently used should be substituted by the model considering the power in the grid 110 kV and below. The results are available to power network planning and operation in practical work.