Sang-Guk Lee’s research while affiliated with Korea Hydro and Nuclear Power - Central Research Institute and other places

The reliable operation of onsite emergency diesel generator(EDG) should be ensured by a conditioning monitoring system designed to maintain, monitor and forecast the reliability level of diesel generator. The purpose of this paper is to develop condition diagnosis algorithm(logic) and analysis program of engine for the accurate diagnosis in actual condition of emergency diesel generator engine. As a result of this study, we confirmed that developed engine condition diagnosis algorithm and analysis program could be efficiently applied for actual EDG engine in nuclear power plant.

In this study, we performed theoretical analysis and test to identify an effect that lubricant performance has on actuator output thrust of MOV. Particularly, we introduced Stem Friction Coefficient (SFC) concept that means friction coefficient between a stem nut and a stem screw. By using SFC concept, an effect of lubricant performance on the actuator output thrust was analyzed quantitatively. The first phase test was performed to compare the lubrication performance between new lubricant and old lubricant and the second phase test was performed to compare the lubrication performance for the three kinds of representative lubricants (EP0, EP1, EP2) being used in Korea nuclear power plants. According to the test results, SFC value of old lubricant appeared higher than that of new lubricant and a old lubricant at TST point generated lower thrust value than a new lubricant at the same torque value. We can verify that the effect of lubrication performance has on power generated in an actuator was very large and SFC was a very useful variable in analyzing lubrication performance quantitatively.

Stem friction coefficient is a coefficient that represents friction between thread leads of the stem and stem nut. It is an important factor to determine output thrust delivered from the actuator to the valve stem in assessing performance of motor operated valves. This study analyzes the effects of changes in differential pressure on stem friction coefficient, and determines the bounding value of stem friction coefficient. A dynamic test was conducted on multiple flexible wedge gate valves in various differential pressure conditions, and the test data was statistically analyzed to determine the bounding value. The results show that stem friction coefficient in middle and high differential pressure is influenced by fluid pressure, while stem friction coefficient in low differential pressure is almost not affected by fluid pressure. In addition, it is found that the bounding value of stem friction coefficient is higher in a closing stroke than in an opening stroke.