Open‐phase temporary overvoltage before and after an intermediate subsation accessing a long distance transmission line

AbstractIn transmission lines, shunt‐reactors are commonly applied to counteract the “Ferranti effect.” However, in highly compensated lines, hazardous overvoltage may occur during unbalanced open‐phase conditions. In addition, when a new substation is put into operation, π circuit can be selected by accessing an existing transmission line and the original shunt‐reactor configuration is maintained. Severe overvoltage may occur on the shunt‐reactor side of the newly installed transmission line. In this study, we analysed the effects of compensation, neutral‐reactor, and system frequency on open‐phase overvoltage. The maximum deviation of system frequency is  <±0.5 Hz, therefore, we suggested maximum critical compensation of the shunt‐reactor under different proportional coefficients of neutral‐reactor. We analysed the impact of line division, when an intermediate substation is accessed, and a risk range in which the substation located may cause severe overvoltage was proposed. Finally, according to an actual line division project, we optimised the original configuration scheme of the shunt and neutral‐reactors. We used electromagnetic transient simulation to verify whether severe overvoltage occurred before and after the power station is accessed. The study results may provide guidance for selection of the π circuit accessing point and for optimising the configuration of the shunt and neutralreactors.