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armstrng2141finl - 2.141 Term Project Pump Fault Detection...

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2.141 Term Project Pump Fault Detection and Diagnosis (FDD) Based on Electrical Startup Transient 2002.12.12 Peter Armstrong The repeatability of start transients for a typical 3-phase, single speed HVAC pump is illustrated in Figure 1. The plot shows six smoothed 1 time histories of phase-to-neutral power observed on the A-phase. We wish to model the system (or as much of it as necessary) to explore the possibility of using this relatively easily observed signal [Laughman] as a basis for fault detection and diagnosis. Figure 1. 50-hp chilled water pump startup, A-phase power, 120Hz sampling, 6 repetitions A common approach to fault detection and diagnosis is to model the target system, then simulate its behavior under various conditions. After the correctly functioning system has been characterized, various faults can be modeled and the simulations repeated. At this point there are two possible paths. One is to find distinctive features of the responses that can be associated with each fault. This may be difficult. The other approach is to use the simulation results to see if system parameters, changes in which might be associated with various faults, can be estimated from the responses. This is also difficult. In either case, the first step is to model the system in order to better understand it, to find out how it responds under various conditions—special excitations as well as typical—and to learn if the responses contain information that could be used to identify faults or nascent failure by one of the two diagnostic paths. At some point, real data is needed to test detection and diagnostic procedures. Since we already have measured responses of a real system, the main goals of this term project have been to understand the system and develop a verifiable model, i.e. a model that reproduces the measured responses. System Overview . The main elements of the system to be modeled are the power source, motor, pump, and hydraulic load. Inertances and resistances are likely to be important determinants of startup behavior. For example, on the electrical side, inrush current is governed by source [Shaw, 2000] and stator resistances and inductances. The inrush current time constant is likely to be small compared to other system time constants. The flow transient is governed, in the fluid 1 by a “spectral envelope” filter (Appendix A)—a low-pass filter found [Leeb] useful in categorizing the start transient signatures of individual electric loads of buildings and other energy-using facilities. Children's Court 17 June P4, 6 reps 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000 1 13 25 37 49 61 73 85 97 109 121 133 145 157 169 181 193 Time (1s/tick) signal (A-phase A) 1 2 3 4 5 6
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Armstrong 2/29 domain, by inertances and resistances in the piping circuit; it may, depending on coupling and relative time scales, be significantly affected by motor and pump rotor inertances.
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