Effect of interphase magnetic coupling of shunt reactor on transmission‐line open‐phase overvoltages and neutral reactor optimisation.

This study thoroughly studies overvoltages appearing on the isolated phase (s) of shunt reactor compensated transmission‐lines when remaining phases are left energised. The voltage that appears on the isolated phase would settle to a steady‐state component induced from the energised phases. This endures until all other phases are disconnected or the isolated phase is re‐energised. Reactors with different zero‐ and positive‐sequence reactances are less common but not rare. Taking this point into account, a general model is introduced for three‐phase reactors involving those with interphase magnetic coupling. Accordingly, a rigorous analytical formulation is developed to prevent open‐phase damaging overvoltages. As proposed, this is achieved by installing a suitable neutral reactor whose optimal value is obtained using the extracted closed‐form equations. It is shown that in the case of shunt reactors with interphase magnetic coupling, open‐phase overvoltages are more likely to arise even for small degrees of compensation. Based on the defined objectives, a range is determined for the neutral reactance in which no open‐phase overvoltage would appear. This provides a high flexibility in sizing the neutral reactor considering technical and economical limitations. The accuracy of the employed models and effectiveness of the optimised neutral reactance are further illustrated through extensive simulation studies using the electromagnetic transient program EMTP‐RV. [ABSTRACT FROM AUTHOR]