An automated system for motor-operated valve diagnostics

This paper reports that proper performance of safety and control systems in nuclear power plants depends heavily on motor-operated valve (MOV) reliability. MOV operation also has an impact on plant availability. estimates indicate that valve-related problems in U.S. nuclear power plants result in 20% of unscheduled shutdowns. Predictive MOV maintenance avoids unscheduled outages and exposes unnecessary maintenance procedures that might otherwise take place during scheduled outages. For a predictive maintenance program, it is necessary that the degrading mechanical and electrical behavior of MOVs be detectable at an early stage and that the time to failure is predictable. Present testing practices do not fully address predictive MOV maintenance, but extensive research and development is underway to improve valve monitoring and diagnostics methods. Valve signature analysis appears to be the most promising new surveillance approach. This is a computer-aided testing method for measurement, management and analysis of MOV operation related time waveforms, such as motor current and valve stem thrust. Waveforms then are interpreted manually by a diagnostic expert.