Electric actuators for nuclear power plants

The valve uses an electric actuator  of ST70/120, which is connected to the valve via a remote transmission device. The output speed of the electric device is high, and the moment of inertia at the start is large, so that the electric starting torque of the valve remote transmission mechanism is greater than the torque protection fixed value of theElectric Actuator, which is easy to cause theElectric Actuatorto start and stop many times, and exerts multiple impacts on the planetary gear carrier of the deceleration mechanism. After multiple impacts, the electric actuator planetary carrier will cause the gear carrier to break, resulting in the unavailability of hand and electric operation of the electric actuator. Analyze several typical electric actuator fault phenomena of the system, and formulate corresponding treatment measures. 1 Fault background and application status A After the main control of the base issued the test instruction, the 1EAS013VB electric actuator could not be opened, and the manual and electric operation of the electric actuator failed, and after disintegration, it was found that the planetary gear bracket inside the electric actuator was broken and damaged, and the output torque of the motor could not be transmitted to the output shaft of the electric actuator. Base B 1EAS013/014VB There is a continuous shaking of the torque rod in the commissioning stage of the electric actuator, and the torque rod continues to shake when the valve is opened and closed at the initial start, and the torque rod moves back and forth with the sound of "da-da-da". C Base 1EAS014VB electric actuator annual inspection switch has obvious jitter when operating the valve, and causes the upstream U, W two-phase fuse of the electric actuator to fuse. According to the feedback from bases A, B and C, the EAS013/ 014VB electric actuator of unit 3/4 of base D contains the valve full open, fully closed, middle position to full open, and middle position to full close to the recording test, and the torque limit switch has obvious jitter phenomenon in this test process.Nuclear-grade electric actuators include SR, ST and Yang Xiu Siemens brands, and Yang Xiu Siemens high-speed electric devices have poor self-locking effect. The SR type electric head at Base D has been discontinued in Bernard, France. Due to the EAS013/014VB of the new unit A/B/C base all use ST70/120 electric actuator, the electric actuator  has high speed and is sensitive to torque changes, and the system belongs to the nuclear safety system, there are clear requirements for the valve opening time, through rigorous demonstration and experiment, the electric device is replaced with ST70/61 type, and the mechanical valve stem becomes double thread, which fundamentally solves the problem of torque jitter after the EAS013/014VB electric head is closed in place. 2 Cause analysis In the case of LOCA or steam pipeline rupture accident in the containment, high-temperature and high-pressure steam is sprayed out, which increases the pressure and temperature in the containment. The function of EAS (Containment SpraySystem) is to reduce the pressure and temperature inside the containment to an acceptable level by spraying condensed vapor to ensure the integrity of the containment.