영광1,2호기 고압터빈정지밸브(TV) 제어루프 이중화 연구

Abstract

In the nuclear power plant, the large scale of turbine is inevitable because of its characteristics using the saturated steam at the secondary side. The facility which surely controls the speed and the load of this large turbine and stops it safely in case of emergency is the DEH(Digital Electro-Hydraulic) control system. The DEH control system for Yeonggwang unit #1, 2 controls of TV(Throttle Valve), GV(Governor valve), IV (Intercept Valve), and RV(Reheat Stop Valve) along with an amount of steam supplied to a high pressure turbine and a low pressure turbine in order to control the number of rotation of a turbine along with the output of a generator. Among them, TV(Throttle Valve) blocks steam incoming to a high pressure turbine in a condition which requires the operation of the turbine to be stopped, and control the speed of turbine when a power plant operates. In addition, TV (Throttle Valve) deactivates a nuclear reactor when 4 valves are all shut down due to valve control signal errors arisen during normal operation. This paper is to analyze current status and classification of failures of a throttle valve controller of Yeonggwang unit #1 & 2 and to improve a throttle valve control loop which is composed a single control loop in order to increase the reliability of an equipment and to enhance the maintenance convenience of an equipment and the stability of turbine output control. In general, a control loop of TV is composed a RVP (R-Line valve positioner) which is in charge of the control of a valve location at a site upon signals of a controller (controller requested signals), a servo valve which generates a path for a hydraulic system along control signals, LVDT (Linear variable Differential Transformer) which is used for the detection of valve divergence, etc. Failures of compositions of a control loop of TV arisen from January ’06 till the time of writing have been analyzed and it shows that out of 17 failure cases, 8 cases were related with RVP (of 47%) and there were 4 cases of the reduction in output. The analysis of failure cases reveals that a single control loop has a negative side. When individual control equipment is failed, a signal processing process gets stopped and then, TV gets shut down as well. Therefore, in order to improve a TV control system of Yeonggwang unit #1&2, a control loop of TV should be dualized. Dualization can be divided into RVP dualization, servo valve dualization and LVDT dualization, and if dualization is applied concurrently, it could be considered as a system with fault tolerance against a failure of a single control device. In order to verify control features of dualized valve control loop, a dualized control loop was composed for conducting the comprehensive fail-over test which includes a primary/secondary position control module failure test, a servo valve coil opening/short-circuit test, a LVDT secondary coil-1/2 failure test, a serial link failure test, etc. and simulations were performed. It is anticipated that the aforementioned study results would be used as reference data for improving the reliability of Turbine Control System (DEH) of an actual power plant.