One of the most important faults that occurs in an energy system is the failures by voltage instability. Our research proposed a methodology for the detection of failures due to voltage instability in dynamic simulations for the Center-South Transmission System of Peru. The specific behavior of the complex load is described when it is subjected to sudden voltage variations in the connection node, due to various disturbances that occur in the transmission network. Steady state analysis models such as Schlueter or Lyapunov are used here as a measurement methodology to analyze the changes in voltage instability of the system. The case study here is the disconnection of line 5011 (Chilca Nueva-Fenix), which had a replacement time of 4h 14 min and an interrupted power of 529.6 MW.