Studies On Structure Adaptability Of Shandong Transmission Network Under UHV Integration

According to "West Power to East" policy proposed by National Energy Administration, three projects of EHV in Shandong Grid are planned and designed, and all of the three projects are approved. The three projects are:"East Rift" UHV AC, "North Transverse" UHV AC, Shanghai temple to Linyi substation UHV DC. As "East Rift" and "North Transverse" UHV AC come on stream, the power network structure of Shandong Grid is continuously strengthened, but some disadvantages follow. Three-level electromagnetic loop circuit 1000/500/220kV appears in regional network of Shandong Grid. Besides, the short-circuit current level of some substations is excessive, even more than the current breaking capacity of breakers. The appearance of three-level electromagnetic loop circuit makes power transfer between different voltage classes and the short-circuit current exceeding more serious. To solve these problems, reasonable current limiting scheme and opening schemes need to be adopted. Aim at these problems, the emphases of this paper are as the follows:1) The model for evaluating opening schemes of electromagnetic loop circuit in Shandong Grid is built. Based on Analytic Hierarchy Process (AHP) and fuzzy math, the fuzzy comprehensive evaluation method executes a quantitative assessment of different opening schemes, with the introduction of some evaluation indexes. The evaluation model is applied to assess some opening schemes of three-level electromagnetic loop circuit in Shandong Grid, Case studies performed on the actual power system demonstrate the effectiveness of this proposed model and method.2) The comprehensive optimal deployment model of short-circuit current limiting measures for Shandong Grid is built. Firstly, this model takes advantage of GA algorithm to get scheme sets, then the fuzzy comprehensive evaluation method executes a quantitative assessment of different opening schemes, rational and economic scheme is get. Before the scheme optimization, to reduce computational complexity, branch screening strategy is applied. The basis of screening is the sensitivity of each ordinary branch. In the end, the comprehensive optimal deployment model is applied to find optimal solutions for the short-circuit current exceeding sites in Shandong Grid. And Case studies performed on the actual power system demonstrate the effectiveness of this proposed model and method.3) A multi-objective optimization model of current limiting scheme for multi-infeed HVDC systems is built. Based on NSGA-II algorithm and branch screening strategy, this model automatically generates current limiting scheme which is optimized. This model is to minimize total investments and short-circuit capacity margin and to maximize weighted multi-infeed short-circuit ratio. Then, case studies performed on IEEE 39-node network indicate the effectiveness of the proposed model and method in simulation results.