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Turbine Unit Bearing Temperature False Tripping: Causes and Solutions

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**1. Introduction** Bikou Hydropower Station is equipped with three mixed-flow hydroelectric generating units, each with a capacity of 100MW, manufactured by Harbin Electric Machinery Factory. Initially, the temperature measurement system used ratiometric equipment with reed switch contacts. However, due to low reliability, it affected the monitoring of unit temperatures and the accuracy of readings taken by operators. In late 1996, the temperature monitoring circuits of the three units were modified to interface with the computer monitoring system. The DAS-IA/B series multi-function inspection instrument from Hefei University of Technology High Technology Industrial Company was selected. Despite its use, the system often experienced abnormal displays, communication failures, poor anti-interference capability, and wiring issues, leading to sudden temperature spikes. The temperature measurement points are located in a strong electromagnetic environment, which further complicates accurate readings. Some temperature sensors frequently triggered high-limit alarms, causing server crashes in the monitoring system. **2. Analysis of Bearing Temperature False Tripping** On August 30, 2001, during normal operation of the 1# unit at 100MW, the temperature inspection instrument displayed an abnormal reading. After checking the stator temperature circuit, maintenance personnel found that the terminal of the resistance thermometer (02) was loose. When the multimeter test pen touched the common terminal, the resistance value fluctuated, causing the temperature inspection instrument to exceed the 65°C threshold, triggering a trip. This resulted in the outlet switch 2201DL tripping, the emergency stop solenoid valve activating, and the unit load dropping to zero. Post-incident analysis confirmed that the loose common terminal caused the temperature values to rise sharply. Repeated simulations showed that even when the temperature resistor was short-circuited or open, the temperature reading remained zero unless the common terminal was loose. This confirmed that the false trip was due to a loose connection. In the microcomputer monitoring system, the bearing temperature trip logic relied on data from the temperature inspection instrument. However, this method had several drawbacks: - High disturbance from the generator’s magnetic field led to data drift. - Difficult to eliminate interference from on-site signals. - If the temperature inspection instrument failed, all temperature protection would be disabled. **3. Renovation Plan for the Temperature Trip Circuit** To address these issues, the following improvements were implemented: **3.1 Upgrade the Temperature Measurement Circuit** A temperature control cabinet was installed near the unit. The original temperature control loops for the water guide, thrust, and upper bearings were separated from the inspection instrument. Each unit was equipped with an XMT-800 digital controller, which independently collected and processed temperature data, then issued trip commands. **3.2 Replace Temperature Measuring Resistors** Except for the stator temperature package, which could not be replaced, other sensors used Pt100 platinum resistors instead of Cu53 copper resistors. This improved accuracy and stability. **3.3 Dual Temperature Measurement Points** Each critical temperature point was monitored using two components—one input to the microcomputer controller and one to the local control unit (LCU). Only when both sensors showed high temperatures would the unit trip. A time delay was also added to distinguish between real and false signals, improving system robustness. **4. Key Considerations During the Renovation** **4.1 Independent Temperature Trip Control Loop** An independent control loop was established, separating the temperature trip detector from the patrol instrument. The original holes were used to install 200mm-long thermometers with a diameter of 10mm. Each bearing's temperature was led to its own controller, making maintenance easier and reducing mutual interference. **4.2 Proper Placement of Thermometers** Thermometer leads were made of oil-resistant, high-temperature twisted-pair shielded cables, with the shielding grounded properly. Terminal connections were reinforced to prevent interference. **4.3 Post-Renovation Testing** After installation, all resistance thermometers were tested for open circuits, short circuits, and grounding issues. **4.4 Sensor Placement and Response Delay** Due to the lag in temperature response, thermometers were placed as close as possible to the tile surface to minimize hysteresis and temperature decay. **4.5 Timing of the Renovation** The temperature trip circuit renovation was only carried out during the unit’s overhaul. **5. Conclusion** After implementing the above improvements, the 2# unit was officially put into operation on February 6, 2002, and operated safely for over two years until July 31, 2004. The transformation proved successful, ensuring safe and reliable operation. --- **Related Bearing Knowledge** Preparation for the installation of NSK rolling bearings. Locking methods for two bearings. Strategies to reduce bearing noise. Detailed discussion on the repair of centrifugal compressor thrust bearings and pump shaft bearings. This article is linked to http:// Please indicate the bearing network http:// Previous: Analysis of the application of SKF bearings Next: The development and classification of spherical roller bearings

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