Research On Line Selection Device Evaluation System For Small Current Grounding System

Line selection theory has been a big problem in work of relay protection about 10 k V distribution network, however, resonant grounding system is more difficult than it. Though kinds of line selection devices becomes more and more varies, the line selection doesn’t effect well, false and missing results still exists according to operating results at worksite and statistics of relevant sectors of the grid. How to evaluate line selection devices those meet grounded system requirement has become an important and urgent research topic.In this paper, line selection device of neutral ineffectively grounded system is studied based on present situation of line selection devices and method, doing research as follows:(1) Changes of zero-sequence current and zero-sequence voltage are deeply analyzed before and after ineffectively grounded system happens single-phase ground fault.(2) Line selection device evaluation system of neutral ineffectively grounded system was proposed based on the theoretical analysis of neutral ineffectively grounded system fault. The system mainly includes three parts: 1) A simulation testing platform of neutral ineffectively grounded system is built based on RTDS. 2) A close-loop testing hardwire is constituted. 3) A line selection device evaluation system of neutral ineffectively grounded system is constructed.(3)Function of RSCAD modules is summarized in detail. Testing platform of fault model simulation for 10 k V neutral ineffectively grounded system is designed by selecting and calculating each module’s parameters. Construction of close-loop testing system and work principle of RTDS is instructed, in particular, the function of customized power amplifier is illustrated. It attaches importance attention to the process of line selection according to single-phase of different grounding resistance and different fault location. Then, the validity and feasibility of the simulation model is verified.(4) Grey analytic hierarchy process is applied to the evaluation of line selection devices of neutral ineffectively grounded system, which is considered in subjective and objective mind, which avoids subjective consideration that it can be assessed but can not be measured,meanwhile, it avoids subjective consideration that it can not be assessed but can measured as well. Optimal number of columns of index is obtained to refer to by using hierarchical model.Judgment matrix is written though scale method of 1 to 5, the evaluation index weights is determined, correlation coefficient specification is treated in standardized way,thus selecting the optimal results. The merits of alternative means of alternative devices is evaluated, combining examples, which verifies validity of evaluation systems for line selection devices.