Abstract :This paper presents a new static network equivalencing technique that take in to consideration the influence of changes occurring in the reduced system based on voltage phasor measurements from this system. The method was developed around the REI equivalent, but in principle it can be used with any other equivalencing technique. Numerical simulations have shown that real-time measurements provided by PMUs installed on the buses of the external system can considerably improve simulation results produced by traditional REI equivalents for the operating conditions in the internal, obser ved power system.