On 4 February, 1997 the plant was under 365 MW electrical power operation with two working turbogenerators. At 6:31 a.m. one of the turbogenerators was disconnected from the grid and tripped by the control and protection system. The reactor power was decreased in order to maintain the parameters of primary and secondary circuits. At 6:34 the reactor was shut down by the control and protection system because of drop of level in the steam generators 1-3. The investigation revealed that the cause of generator disconnection was short circuit in one of the relays on the protection system of the disconnected generator. The plant was returned to normal operation the same day after replacement of the failed relay. The deviation caused neither on-site nor off-site radiation impact. Justification: As full safety functions were available, the event is rated at level "0" as per user's manaul, part III.