a question about breaker

 Recenetly, I built a multi-machine power system model to simulate the test of cut generator of 25MW) of the generator by Matlab7.1. However, I found that the steady-state active power output for the original 25MW generator is 0.50125 p.u.), but after the circuit breaker installed in the system, the steady-state active power output becomes 0.225 (p.u.)or so, I want to know why this is? It stands to reason, the installation of circuit breakers should not affect its active power, how to correct it?