With the extreme use of the transmission lines, the voltage stability problem, or more properly, the voltage security problem has appeared. The voltage security condition assessment is achieved using the computational program ESTABTEN. The calculated indexes are based on a system operation point and on a linear model of load flow equations, likewise the ANAREDE load flow function. It is important that the mathematical models of systems, equipments, control devices and limits are compatible in both programs. As the load flow program is continually extended, the ESTABTEN program is to have its capability enhanced in order to attend the study requirements. This work is concerned with the steady-state modelling of some special equipments of the transmission network and its incorporation to the voltage security assessment function. The equipments considered were: direct current link (DC link), static VAR compensators (SVC), HVDC/CCC and lines with series controlled compensation (TSSC).Numerical examples are presented to illustrate the necessity of realistic modelling.