One of the most important phases of power systems planning, is the examination of its dynamic behavior. It is convenient under this aspect, to have the models of all components pertaining the system, as close as possible to the real conditions of operation being of particular interest a good representation, mainly of the machines (generators and synchronous compensators). Lately, the static compensators (SVS), have been an important component in the control of reactive power for the UHV electrical systems. Due to this fact, the digital programs used until then, had to be conveniently modified so as to consider this new equipment. The purpose of the present work, is to introduce the representation of the SVS in the stability programs. Special care will be give to the SVS controlled by thyristors (TCR, TCT, TSC or mixed), in which the intervention of specific control systems takes place. Based upon the proposed models, an analysis of the operation of the thyristors SVS in permanent and transient regimes is performed. Together with the presentation of various types of thyristors SVS, it is introduced methods to determine nominal values, main operational characteristics, always comparing, when possible, to other types of static compensators, as well as, with the synchronous compensators in operation.