On January 19, 2011 the Laguna Verde NPP Unit 2 was operating at 43.2% of rated power in process for testing. According to the sequence of events, it follows that: While testing for the load rejection signal, the main turbine incremented its speed. The main turbine control valves started to close while controlling the turbine speed. The pressure at the first step in the turbine was at 17 kg/cm2, with the control valves closed. Then, the pressure at the first step started to decrease until 4.6 kg/cm2. There was a main turbine trip signal due to the actuation of the Speed Acceleration Limiter, but this signal trip did not actuated the RPS, instead there was a reactor trip due to high pressure signal of the reactor pressure vessel. The cause was that the during the power rising process after testing of the Moisture Separator Reheaters the alarms associated to the bypass of the signal trip for the main turbine trip were not reestablished, therefore the during approximately 40 minutes the reactor operated without the reactor trip signal of the main turbine trip.