Yunnan Power Grid Black Start Empirical Analysis

With the scale of the power system enlarging and the capacity increasing, more strict requirements for power supplying safety are proposed. Black start, the restoration of power system after blackout due to certain faults, is important to ensure the system secure. By using electro-magnetic transient program(EMTP),aiming at several operation modes in black start scheme of Yunnan network ,this thesis calculated self-excitation, power frequency overvoltage, switching overvoltage, switching on unloaded transformer overvotage.Whether the generator's self-excitation takes place during black start is a factor for determining feasibility of restoration schemes. In this paper, criterions are given after the fundamental of generator' s self-excitation is introduced and a simulation system based on MATLAB is designed. The mechanism of internal overvoltage in restoring the non-loaded long distance overhead line during the power system black start process is analyzed, and the calculation model of overvoltage is established with ATP-EMTP. The general software for simulation of power systems is applied to calculate power frequency overvoltage and switching overvoltage for checking. This study is useful for formulating practical black start schemes. The switching on unloaded transformer overvotage has scarcely mentioned in literatures, but for black start, this kind of overvoltage caused by operations such as a bus connected a long transmission line switching on an unload transformer should be considered an treated seriously. Special research on it is carried out in this paper,Though the above study and analysis some black start plans for Yunnan network have been evaluated, potential problems found and corresponding countermeasures developed. An academic basis has been founded to constitute a feasible black start plan for Yunnan networkThe special switching manipulation and mode of operation in power system black start is studied. The effects on longitudinal differential protection of 500kV overhead lines manwan to caopu and dachanshan to baofeng in yunnan powergrid are discussed. The calculation model of line longitudinal differential protection is established with ATP-EMTP ,and some priciples of line longitudinal differential protection are presented in this paper.