EME Associates built a test stand to analyze nuclear reactor coolant pump bearings. The stand supports a 500-hp motor, a 600-hp electrical drive and a bearing assembly. Means are provided for applying both horizontal and vertical loads to the bearing assembly to simulate extreme stresses, temperatures and loads that could be expected when the bearing seal leaks lubricant, or when the bearing simulator fails for other reasons. The ZonicBook records these variables, and with the help of eZ-TOMAS software, analyzes the data that can predict a possible failure.

Nuclear power plants depend on electric motor-driven pumps to circulate coolant through a closed system of pipes to help dissipate excess heat. These machines, reactor coolant pumps (RCP’s), must be monitored continuously to ensure dependable operation. Resistance temperature detectors ( RTD’s) located on the pump’s bearings measure temperature and send the signal to an automatic alarm and control system that quickly alerts operators of any status change. RCP bearings are likely suspects for failures. One failure mode is a bearing seal that leaks lubricant and can become a fire hazard. Because of their importance, monitoring RCP bearings is a high priority, and usually, multiple sensors are installed on each bearing to provide redundancy.

Because issues with bearing seals have been a reoccurring nuclear power plants, the Nuclear Regulatory Commission has issued a multilevel procedure for powering down facilities when seal problems occur. One company has gone even further, initiating a special program to research the cause of seal failures and developing a method for testing thrust-bearing seal leaks outside the machine. The program uses a simulator composed of a test stand that accommodates a large motor and bearing assembly; hydraulic actuators that place external, vertical and horizontal stresses on the bearing shaft; and a data acquisition system that monitors temperatures, forces, pressures, oil flows and vibration in the motor and bearing.

Stress analysis engineers at EME Associates, Pittsburgh, Pa., designed and developed the test stand and appropriate instrumentation. EME had several dual-channel data acquisition systems from which to choose, but the design eventually called for more than 50 channels of simultaneous data collection. Clearly, the EME team had to find a compact data acquisition system capable of handling that number of channels and flexible enough to accommodate a wide variety of sensor types.

IOtech's Solution
After investigating several possible systems, the EME team selected the IOtech ZonicBook for the application. Although it was the first IOtech system with which they had experience, Christopher Mascaro, an electrical engineer at EME learned how to use it in less than a day. The data acquisition system let him connect 56 channels with a mix of sensors that included RTD’s, flow sensors, pressure sensors, tachometers and proximity probes.

ZonicBooks are used to monitor the bearings in reactor coolant pump simulators. Thermocouples measure the bearing temperature, proximity sensors measure vibrations and the software generates Bode plots, which give the vibration specialist a means to detect, analyze and repair bearing failures.

“The original design called for about 20 sensor channels,” says Mascaro, “but it expanded to 56 channels as the project developed”. Six WBK18, 8-channel dynamic signal conditioning modules were added to the ZonicBook to expand the channel count, as well as two DBK84 thermocouple modules to handle multiple temperature channels. “The ZonicBook and expansion modules worked out extremely well for us because they are flexible enough to handle the wide variety of variables in our customer’s specifications,” says Mascaro. “We could monitor the data in real time and track changes as they appeared.” The parameters measured included pressure from 0 to 60 pounds per square inch gauge (psig), temperature from 80° to 350°F and shaft speed from 0 to 1,190 rpm.

In addition to the originally specified sensors, proximity sensors were added to measure vibration and the shaft’s axial position. Other sensors were added to measure oil level. Hydraulic cylinders were installed on mounting collars to apply side loads to the bearings and on thrust runner reaction bearings to apply vertical loads. In addition, load cells were installed on these actuators to measure the amount of force applied to the bearings.

“The simulator stand had to be compact,” says Mascaro. “We built a single control panel to contain the ZonicBook, signal-conditioning modules, computer, TV monitor and digital video recorder.” EME also used the IOtech DBK48 Signal Conditioning Module containing non-destructive test relay outputs to shut down the motor in the event of an over-temperature or over-speed condition, excessive vibration, low oil level or excessive vertical or horizontal thrust.

"The eZ-TOMAS software supplied with the ZonicBook was easy to use and let me construct Bode plots of the vibration,” says Mascaro. “We were able to commission the system and turn it over to the customer within three months, and we taught (the customer’s) engineers how to use both the software and hardware in less than a week.”