Steps and precautions for reinstalling the turbine vibration and displacement probes

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The quality of reinstalling the vibration and displacement probes of steam turbines directly affects the accuracy of unit condition monitoring as well as equipment safety; it is necessary to follow the specifications strictly. The following are the installation steps and precautions: I. Preparation before reinstallation 1. Preparation of tools and materials Special tools: torque wrench (matching the specifications of the probe mounting bolts), feeler gauge (with 0.01mm precision), dial indicator, level, alcohol/anhydrous ethanol (for cleaning), fine sandpaper (#400 or finer, for lightly treating the contact surfaces). Consumables: high-temperature sealant (for sealing probe cable pass-through holes), insulating gaskets (if required), and a clean cloth. Technical documents: Probe installation drawings (indicating the installation location, clearance values, and tightening torque), equipment manual (confirming the probe model and installation specifications). 2. Probe and on-site inspection: Probe inspection: No visual damage; the cable’s insulation layer is intact, the shielding layer shows no breaks, and connections (such as BNC connectors) are clean with no oxidation ； Use a multimeter to measure the probe resistance (such as the resistance of the eddy current probe coil, typically 5–25Ω, depending on the model) to ensure there are no open circuits. Mounting seat inspection: There are no impurities such as oil or metal shavings in the probe mounting hole (or bracket), and the threads are in good condition with no stripping ； The surface to be tested (such as shaft journals) should be smooth, free of scratches or rust; if necessary, it should be gently polished with fine sandpaper and then cleaned. II. Steps for reinstalling the vibration probe (taking the eddy current vibration probe as an example) 1. Position the mounting bracket: Determine the probing direction of the probe according to the drawings (horizontal/vertical/axial), fix the bracket to the bearing housing or cylinder block, and use a level to adjust the plane of the bracket so that the probe’s axis is perpendicular to the surface being measured (deviation ≤5° to avoid signal distortion). 2. Initial installation of the probe: Clean the probe head and the surface of the shaft journal being measured (wipe with alcohol), then gently rotate the probe into the mounting hole until the probe head makes contact with the surface of the shaft journal (with a slight resistance felt). Mark the position of the probe at this point (for example, make a mark between the probe nut and the mounting base). 3. Set the installation clearance: Determine the standard clearance based on the probe model (for example, eddy current probes typically have a clearance of 1.0±0.1 mm; see the manual for details), and adjust it as follows: Method 1: Retract the probe from the contact position, measure the clearance using a feeler gauge, and fine-tune it gradually until it reaches the standard value ； Method 2: Power the probe, use an oscilloscope or preamplifier to monitor the output voltage, adjust it to the midpoint of the linear range (e.g., 0V corresponds to a 1mm gap in a -2V to +2V linear range), and then lock the nut. 4. Fixing and sealing: Use a torque wrench to tighten the lock nut to the specified torque (for example, 15–20 N·m for M10 bolts); be careful not to over-tighten, as this may damage the threads or the probe) ； The cables should be routed along fixed channels to avoid too small a bending radius (≥5 times the cable diameter), and secured with clamps at intervals of ≤300 mm. Sealing compound should be applied at the cable pass-throughs to prevent water and dust from entering. III. Steps for reinstalling the displacement probe (taking the axial displacement probe as an example) 1. Determine the measurement zero point. The axial displacement probe is used to measure the relative position between the rotor thrust disc and the thrust bearings; therefore, it is first necessary to move the rotor to the “operational zero point” (for example, by bringing the thrust disc into close contact with the working surface, using a jack or a rotor turning device). 2. Install the probe holder. The holder should be fixed to the cylinder block or bearing housing, ensuring that the axis of the probe is perpendicular to the side of the thrust disc (with a deviation of ≤3°); the probe tip should be aligned with the edge of the thrust disc (avoiding chamfers or grooves), and the measuring surface must be flat. 3. Adjust the installation clearance: Set the initial clearance according to the diagram requirements (e.g., 1.5 mm). The method is the same as that for the vibration probe: Mechanical method: Use a feeler gauge to measure the distance between the probe and the thrust disc ； Electrical signal method: Monitor the output voltage and adjust it to the midpoint of the linear range (e.g., 0V corresponds to 1.5mm). 4. Locking and identification: The locking nut should be tightened to the specified torque, and a permanent mark should be made between the probe and the mounting base (such as using a stamping tool) to facilitate subsequent checks to determine whether it has become loose ； Record the installation clearance value and the corresponding output voltage as reference data. IV. Precautions for reinstallation 1. Prevent mechanical damage – The probe head is a precision component (such as the coil of an eddy current probe); it must not be subjected to collisions or impacts. Handle it gently during installation to avoid direct contact with the shaft journal ； If the surface to be tested has rust or scratches, it should be gently polished with fine sandpaper (in a direction perpendicular to the axis), but polishing should not be done to such an extent as to change its dimensions. 2. Electrical performance assurance: The cable shielding layer must be grounded at one end (usually on the preamplifier side) to avoid interference caused by multiple grounding points ； If insulation is required between the probe and the mounting base (for example, in cases where insulation from ground needs to be monitored), insulating gaskets must be installed. After installation, the insulation resistance should be measured using a megohmmeter (≥100 MΩ). 3. Match with the unit condition: The rotor must be at rest (the barring gear stopped) during reinstallation, to avoid inaccurate clearances resulting from adjustments while the rotor is in motion ； Before reinstalling the axial displacement probe, it is necessary to ensure that the clearance of the thrust bearing is normal and that the rotor is not stuck; otherwise, it will affect the zero-point setting. 4. Reinspection and recording: After reinstallation, recheck the gap value (using a feeler gauge or electrical signals) to ensure that the deviation from the standard value is ≤0.05mm ； Record the data from the installation process (clearance, voltage, torque), compare it with historical data to confirm there are no abnormalities ； Perform a static verification before starting up: rotate the rotor and check whether the vibration/displacement signals change normally with position, without any jumps or loss of signal. 5. Safety regulations: Wear a safety belt when working at heights, and prevent tools from falling when operating in confined spaces (use tool straps to secure them) ； After reinstallation, clean the area to ensure that no foreign objects remain (such as feelers or rags), to prevent damage to the equipment when it is turned on. By strictly following the above steps and precautions, the installation accuracy of the probe can be ensured, providing a reliable basis for the accurate monitoring of turbine vibration and displacement, and preventing false alarms or equipment failures caused by improper installation.