TQNPC Primary Heat Transport Pump Shaft Vibration Diagonosis And Solutions

After commercial operation of the two CANDU units of the Third Nuclear Power Company (TQNPC), the key equipment, primary heat transport pumps (PHT pumps) had a high vibration problem, the shaft displacement for 6 out of 8 pumps are between 0.14~0.17mm, exceeding the allowable value of 0.127mm. The plant designer,the Atomic Energy of CANADA limited (AECL) and the pump manufacturer SULZER made many efforts on this problem, they provided some traditional method to lower the values for about two years, but no significant progress, the values were still far away from the allowable values of 0.127mm. If this high vibration problem could not be solved, it has the potential risk to the long-term, safe and stable operation of the plant.To identify the root cause of this problem, the author used Fast Fourier Transform (FFT) method, and according to the international standards and related resonance theory, to analyzed the PHT pumps vibration data. By analysis of the PHT pump's vibration signal using the spectrum method, the conclusion was made that the probable reason of high vibration is the resonance of the bracket.Since identified the root cause, the current bracket's natural frequency was measured by using hammer test and was testified by FEA model. The current bracket was replaced by a modified one. The natural frequency of the new one was also measured by hammer test and calculated by FEA model to make sure the resonance can be avoid. With the confidence of the analysis results, we replaced the brackets in the field, and resolved the long-term vibration problem.The author based on the field practice, by using FFT and FEA method and theory for diagnosis, and by applying rigorous analysis and testing, finally found the root cause of the problem. This also provided a method and way to solve big rotating machine vibration problems.