Pump system characterization and reliability enhancement Page: 4 of 13
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There is little that needs to be said about motor failure data. The failure rate for motors
is relatively low; when failures do occur they are generally severe, and the failures involve
primarily bearing and stator degradation.
2.2. Circuit Breakers
As mentioned, circuit breakers experienced more significant failures than pumps
themselves (i.e., 81 failures vs. 75 failures) based on the two year study [3). In a high percentage
of cases, the failures are quite severe in that they prevent the pump from performing its intended
purpose. In fact, the four most frequent indicators of circuit breaker failure in the two year study
are failure of breaker to close (32%), pump stops/spurious trip (13%), failure of the circuit
breaker to charge springs (13%), and failure to trip (I 1%).
The failures are spread over many component areas as indicated in Fig. 3 and involve
various types of electro/mechanical components. The failure mechanisms undoubtedly are also
diverse. These considerations suggest that it will be a formidable challenge if corrective action
or reliability improvement is sought.
S15 1 2 1
z 10 9
JU j~ .Q Z ,
Fig. 3 Circuit breaker failures by afected area
2.3. Turbine Drives
The "turbine drive" is defined as an assortment of components (e.g., numerous steam
valves and speed control devices) combined with the turbine drive to create a turbine drive
system. Because of their small population, Code testing of pumps involved turbine drives in only
3% of the cases. The turbine drive failure rate is several times the rate for pumps and circuit
breakers. This is of much concern since turbine drive pumps are so important in mitigating
accidents involving station blackout failures.
3. PUMP SYSTEM TESTING AND INDUSTRY NEEDS
Significant failures are discovered through Regulatory or Code testing in pumps much
more often than in other components of the pump system. In pumps, Code testing reveals 45% of
the failures while it reveals only 13% of the failures for motors and 0% for turbine drives and
circuit breakers. Even for the pump itself, the testing is of narrow scope. Code testing is
effective only in detecting degraded hydraulic performance; its use of pump shaft vibration
velocity to detect bearing failure is only effective in cases where bearing degradation is severe.
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Staunton, R.H. Pump system characterization and reliability enhancement, article, September 1, 1997; Tennessee. (digital.library.unt.edu/ark:/67531/metadc694411/m1/4/: accessed November 18, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.