Abstract: Themechanical impurity of lubricating oil, oil mud and varnishmay lead to abnormal working of the turbine speed control system and cause large fluctuations in turbine speed.The electro-hydraulic converter has poor adaptability to oil and its own stability is not good, which may cause frequent faults of speed regulation system as well. This paper analyzes the specific hazards caused by such factors as mechanical impurity of lubricating oil to the electro-hydraulic converter, the pilot valve and the oil relay. It also lists the frequent fluctuation cases of steam turbine speed. Based on the analysis results, it is confirmed that main reasons for the fluctuation of steam turbine speed of the TM-25LP electrohydraulic converter was the deterioration of lubricating oil and the generation of varnish.In order to detect this problem in time, the laboratory index of lubricating oil was increased. Meanwhile, the dual filter was added to the control oil pipe to prevent the influence of mechanical impurity and oil mud on electro-hydraulic converter.Aiming at the problems of the TM-25LP electro-hydraulic converter, upgrading and transformation of the electro-hydraulic converter was carried out. In addition, corresponding targeted measures were proposed to improve the quality of the lubricating oil.

Key words: steam turbine, lubricating oil, quality, rotation speed fluctuation, electro-hydraulic converter, abnormal work, countermeasures