Application of fully automated centralized voltage regulation in transmission system operation management

Abstract

The influence of wind farms, inclusion of distributed energy and the energy market has a large impact on the voltage profile in a transmission system. The Croatian Transmission System Operator HOPS has implemented VVC (Volt Var Control) system which was one of the subprojects included in the EU co-founded Sincro.Grid smart grid project that was financed by the EU CEF fund. The main goal of the project is to raise voltage quality in the transmission network. VVC system is an optimal power flow-based application which calculates the optimal solution regarding the desired objective function, available control variables and a defined set of constraints. To achieve the calculated optimal power system state, control of field devices is included in the process of optimization by shifting tap changer positions or changing setpoint values of reactive power injection. Voltage and reactive power constraints are set accordingly to available regulating devices included in the optimization.

The lack of automatic coordination of reactive power resources motivated this work for implementing an advanced VVC for real time control of reactive power in partially automatic and fully automatic (closed loop) mode using the optimal power flow (OPF) algorithm. Due to its complexity, the closed loop approach of reactive power regulation is rarely used in the TSO community and the HOPS is one of the first TSOs that implemented regulation in such manner. Except fully automatic mode of operation, VVC can be used in semi-auto or manual mode. For a successful implementation several safety algorithms are implement to avoid many unwanted situations in the power system such as voltage breakdown, overloading of regulating equipment and similar