Improvement the reliability of HV ? Power transmission lines protection by means of modern devices and methods

The increased voltage profile due to excess of reactive power in low load operation mode in power grid is observed. Because of HV overhead lines are distant from power generating sources and variable load curve, the voltage profile could grow over nominal level and at the same time power loss would increase. The last is caused by changed reactive power distribution at the system. Commutation process for open-phase mode taking in account residual voltages for 500kV, 300km length HV line is studied. Calculations, performed in presence of controlled shunt reactors, gain special importance. The evaluated parameters are the main factors, which define a necessary number of used reactors. Such HV lines usually equipped with nonlinear overvoltage limiters and therefore then switching line on it is necessary to keep in mind line´s VA function and residual voltages at the points of limiters locations. At the same time at the open-phase operation mode it is necessary to provide protection for overvoltage limiters. At the next stages the protection of overvoltage limiters from quasi-steady overvoltages would be considered. The scientific principles of protection from internal and external overvoltages for transmission of electrical energy through polyphase (multi-wire) overhead HV lines, which having been passive before, with help of controlled shunt reactors and selection of VA functions of overvoltage limiters becomes active, are proposed. The selection of residual voltage at the overvoltage limiter and different control functions of shunt reactors are considered.