Motor-Operated Valve Performance Testing and Condition Monitoring Using Data From the Motor Control Center

Abstract

Much progress has been made over the past 20 years at CANDU® nuclear stations to understand and improve Motor-Operated Valve (MOV) performance and reliability. If set up properly, most MOVs show very repeatable and predictable results when tested during outages. In fact, it is believed that, to some extent, a few of the encountered MOV failures stem from repeated maintenance operations and intrusive test methods. In this context, the potential for assessing MOV performance and monitoring their condition using electrical data acquired at the Motor Control Center (MCC) has generated considerable interest over the past few years. The overall approach consists of acquiring current and voltage signals at the MCC to derive motor power and motor torque traces. A correlation between the output parameters typically measured at the valve and the derived motor data is usually established through initial baseline tests. Following subsequent tests at the MCC, several valve performance indicators are derived using the original baseline data and the newly acquired MCC data to assess the valve performance and monitor its condition. The potential benefits from acquiring data at the MCC are the increased trending/monitoring capability and also the cost savings associated with the potential identification of MOVs that may not need “at-the-valve” testing as initially scheduled. This would help reduce maintenance costs and radiation exposure to personnel. At CANDU stations, MOV testing is currently performed almost exclusively at the valve. Voltage and current are occasionally measured at the MCC to generate motor power traces, but not with the intent of performing extensive MCC-based valve diagnostics since most CANDU stations have yet to acquire the tools required for this type of analysis. In this context, a COG (CANDU Owners Group) R&D program was launched to assess the potential and reliability of the various methods/systems used for MCC valve diagnostic testing. This paper summarizes the results of investigations conducted to validate the methodology, recommends the best practices, and helps the stations implement maintenance programs that can take advantage of this diagnostic approach.