Universal Modal Test System

Since early February 2009, some generator group will always make abnormal roaring sound after PM 21:00; people standing by it would feel obvious vibration, on and off and very frequently. At the same time, 35kv grid voltage changes very heavily and the maximum transient difference value is about 0.6KV, but when the gird voltage is relatively stable, the generator group returns to normal.
By consulting experts, the engineer excludes generator group itself to cause the phenomenon. The only one that 35KV electricity grid has effect on the generator group is not a certainty. Because 3320 line heavily load 35KV busbar, and it begin to put into operation at the end of Jan, 2009, the generator group make abnormal sound just as the time.


The testing engineer adopts AVANT MI-7008 data acquisition and signal analyzer with its relevant test software, which is from Hangzhou Econ Technologies Co., Ltd., and uses a triaxial acceleration sensor and a microphone sensor, and then do the abnormal vibration test.
Test results:
The upper sound pressure figure (time-domain and frequency-domain)


The upper vibration spectrum of stator (time-domain and frequency-domain of triaxial signals)


The test data shows that the hydro generator vibrates very lightly in the vertical direction, its acceleration peak value basically appears in the high frequency, which won’t have much effect on it. The vibration features in the horizontal direction of appearing one peak acceleration in near 100Hz is caused by AC power-frequency second-harmonic, when hydro generator group abnormally vibrates, its amplitude will more heavily and appearing irregular change in the second-harmonic, the phenomenon in the horizontal is very obvious. Comparing the acceleration peak value of the upper stator when the hydro generator vibrates normal and abnormally, the engineer find it abnormal vibration, the value of horizontal tangent line is 1.43 times more than that of normal vibration, and the value of vertical line is 1.26 times more than that of normal vibration.
During the whole testing, AVANT MI-7008 data acquisition and signal analyzer shows its features of high reliability and high accuracy. It is matched with the more popular ICP transducer and built-in battery, which don’t connect with power source on the spot and then simplifies the test. Using the offline software to analyze recorded data can acquire the corresponding analysis results and the test report. Therefore, the whole playback analysis can be finished in a very short time.