System-area operating margin assessment and security enhancement against voltage collapse

The (very) short term reactive power scheduling function, to be adopted by ENEL Spa, takes into account the voltage stability requirements in a preventive application of the security function. In this environment the procedure determines the voltage collapse distance of the global system and of the areas controlled by the secondary voltage regulation (SVR) both in short (24 hours ahead) and in a very short term (few hours or fractions of hour ahead). The procedure also schedules the control actions to be taken in emergency states in a preventive way. Area or system-wise indicators, based on nodal sensitivities and/or eigen (singular) value analysis, provide effective measures of the margins of the system with respect to the risk of voltage collapse and the related corrective actions. Applications of the procedure to the EHV network and to a subtransmission area of the ENEL system are presented in the paper