Testing of dc-Powered Actuators for Motor-Operated Valves (NUREG/CR-6620, INEEL/EXT-99-00083)
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Manuscript Completed: April 1999
Date Published: May 1999
K.G. DeWall, J.C. Watkins, D. Bramwell
Idaho National Engineering and Environmental Laboratory
Lockheed Martin Idaho Technologies Company
Idaho Falls, ID 83415-3129
J.E. Jackson, NRC Project Manager
Division of Engineering Technology
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
NRC Job Code W6953
This report documents the results of de-powered motor-operated valve (MOV) research sponsored by the U.S. Nuclear Regulatory Commission (NRC) and conducted at the Idaho National Engineering and Environmental Laboratory (!NEEL). The research provides technical bases to the NRC in support of their effort regarding MOVs in nuclear power plants. The tests described in this report measured the capabilities of typical de-powered valve actuators during operation at simulated loads and operating conditions. Using a test stand that simulates the stem load profiles a valve actuator would experience when closing a valve against flow and pressure, we tested four typical de electric motors and two gearboxes at conditions a motor might experience in a power plant, including such off-normal conditions as operation at high temperature and reduced voltage. We also monitored the efficiency of the actuator gearbox and the efficiency of the actuator-torque/stem-thrust conversion at the valve-stem/stem-nut interface (stem nut coefficient of friction). The testing produced the following results:
For both of the actuator gearboxes we tested, the actual running efficiencies were lower than the published running efficiencies. Below certain motor speeds, actual pullout efficiencies were lower than the published pullout efficiencies. Because of the decrease in gearbox efficiency at low-speed, high-torque operation, increases in motor torque at motor speeds lower than about 200 to 300 rpm failed to produce a corresponding increase in actuator output torque. Thus, in these MOV applications, a de motor speed threshold of about 200 to 300 rpm represents the lower limit for production of usable output.
For the motors we tested, estimates that anticipated linear reductions in both motor torque and motor speed fell very close to actual de motor performance at reduced voltage. However, in some instances the actual and predicted performance fell below the motor speed threshold identified in the previous paragraph. The conventional linear method used in the industry for predicting reduced-voltage-related torque losses underestimated the actual torque losses; this comparison looked at the same motor speed in tests at different voltages.
For all four motors, the actual motor torque losses due to elevated temperature conditions were significantly greater than losses indicated by the manufacturer's published data. The motor torque loss was approximately linear with the change in temperature.
For all four motors, changes in running load had significant effects on valve stroke times. Longer stroke times combined with operation at low speeds and high loads cause additional motor heating and further degradation in motor performance.
At normal voltages and temperatures, two motors produced torque at or above the torque indicated by the manufacturer's published torque/current and torque/speed curves. Two motors produced less torque than indicated by the manufacturer's curves.
For all four motor/gearbox combinations, the high loads and slower speeds had little effect on the stem nut coefficient of friction.
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