This paper proposed a methodology for dividing a voltage control area (VCA) and defined an effective reactive power reserve (EQR) in power flow traceable system. The VCA is decided by simple and general method for tracing the power output of each generator throughout the electrical power network. The reactive power tracing method (QTM) is based on the assumption that, at any network bus, the inflows are proportionally distributed among the outflows. This analysis presented here is of the VCAs problem. Power utilities, for example EdF and CESI, used the concept of the electrical distance to divide the VCA for secondary voltage control. However, we used the QTM in order to decide the VCA. The QTM is very useful that judge a reactive power flow (QF) from generators to loads. This point is different from the concept of the electrical distance. The QTM deals with a general transportation problem of how the flows are distributed in a meshed network. Practically the only requirement for the inflows is that Kirchhoff's Current and Voltage Law must be satisfied for all the buses in the network. This is equally applicable to the QFs. The main principle used to trace the electricity flow is the using a proportional sharing rule (PSR). The distribution matrix of the QF is created, which represents the proportional sharing of the total power injected at certain bus with respect to the outflows from this bus. Each generator cannot give an equivalent effect to the entire system because they cannot be transmitted over a long distance when serious contingencies occur in the power system. Thus, it must be necessary to select the effective generators. The criterion involved is the relation between the generator reactive power supplys and the reactive power demands. The EQR is calculated by linear sensitivities on the basis of this relationship. The computed values are analyzed by the use of time-domain simulations in IEEE-39 system whether the EQR is better than the CQR in terms of voltage stability assessment or not.