水力發電廠豎軸式水輪機振動分析與研究

本論文在探討豎軸式水輪機運轉時發生振動問題，經由測試、診斷分析、平衡校正，探討在不同的位置與負載下振動值與偏轉量(run out)的大小與發生的原因，分析的結果可作為大修時之改善依據。水輪機的振動原因可分為: (1)電氣的原因：如發電機轉子與靜子之空氣間隙不平均、靜子鐵心鬆弛(core looseness)、磁力不平衡、電力輸出的追逐等；(2)水力的原因：如低載或過載時發生之振動、動輪與導翼之距離過小等；(3)機械的原因：如主軸彎曲或下垂、推力軸承調整不良、軸承間隙過大、合心不良、動輪與固定部分接觸、迴轉部份不平衡；(4)其他原因；如水輪機之基礎下沈、機器與建築物之強度不足而共振等。本研究是以明潭水力發電廠─抽蓄式水力發電機之可逆豎軸式水輪機之振動測試與分析。水輪機轉速在400 rpm (三相、18極、60 Hz)，發電機的測試位置包括：上托架、下托架、上軸、下軸，而水車測試位置為水車軸、水車上蓋等。發電機的上托架、下托架，以及水車上蓋之振動值採用速度型感測器，而發電機上軸、下軸，以及水車軸之偏轉量則採用位移型感測器，測試條件分別在負載100, 150, 200, 267 MW等。結果顯示，發電機在平衡試驗後上托架的振動值、上軸偏轉量均有顯著的改善。而下托架、下軸在加配重平衡校正後對於振動與偏轉未見改善效果，因為發電機的原始質量不平衡所致。水車軸在平衡後之偏轉量改善幅度非常大，而水車上蓋於平衡後之振動雖在低載狀態有明顯的改善。然而由頻域響應(frequency response)分析顯示，水車上蓋在140 Hz的高頻時，有相當大的軸向振動，這是機械上的因素造成。此外，水車軸在低頻2 Hz之振動值也很大，此乃法蘭西式水力機組設計的特有現象。因長期運轉造成軸承間隙增加外，另因尾水管長期之大幅度擺動造成剛性變低及支撐結構變弱，均造成尾水管及水車軸振動放大之現象。

關鍵字

豎軸式水輪機；振動值；偏轉量；速度型感測器；位移型感測器；頻域響應

並列摘要

This paper aims to study the vibration problems of vertical-axis type water turbine. The vibration amplitude and run out value at different position of turbine can be determined by measuring, diagnosing, and balance correcting. These analytic results of vibration can be used for processing the main maintenance of turbine. The causes of turbine vibration include: (1) electrical, such as the non-uniform air gap between rotor and stator, stator core looseness, magnetic force unbalance; (2) hydraulic, for instance, low or over load vibration, too small distance between the rotor and guide; (3) mechanical, for example, shaft bending or downcast, too large of bearing gap, misalignment of shaft, rotor contacts the fixed parts, and unbalance of rotating parts; (4) other causes, involve the ground of water turbine sink to a lower level, the resonance of machine and construct and so on. In this study, we measure the vibration at Ming-Tan pumped storage power plant, which owns vertical-axis type water turbines. The revolution of this turbine is 400 rpm (three phases, 18 poles, and 60 Hz). The tested positions of generator include upper casing, lower casing, upper shaft, and lower shaft. Water turbine are tested at turbine shaft and casing. The loading parameters are 100, 150, 200, and 267 MW, respectively. Velocity-type sensors are used for measuring the vibration amplitude of generator’s upper casing, lower casing, and turbine’s casing. Further, the displacement-type sensors can be used for testing the run out of shaft. Results show the vibration amplitude of upper casing and the run out of upper shaft has been improved after balancing. However, the lower casing and lower shaft have no improvement. This is due to the mass unbalancing of upper half part of generator. The turbine shaft’s run outs and vibration amplitudes of turbine casing are better than it is before balancing. The turbine casing also has been improved under lower load. Nevertheless, the vibration value of turbine casing at axial direction is still too large at 140 Hz by analyzing of frequency response. This is due to the mechanical factors, i.e., the friction between turbine and other parts. In addition, a large vibration of turbine shaft at low frequency range, 2 Hz. This is the common appearance of Frances Turbine. These causes are the gap increasing between bearing and shaft, the draft tube oscillation, support structure weakened.