【2026 Transmission Equipment】The difference between turbine shaft vibration and bearing vibration
Thread Content
I. Key Differences • Axial vibration (relative vibration): Measures the displacement of the rotor shaft journal relative to the bearing housing (in μm, peak-to-peak).
• Wear vibration (absolute vibration/bearing vibration): Measures the vibration of the bearing housing/wear seat relative to the ground (mm/s, RMS value).
II. Detailed Comparison 1. Measurement Principle and Sensors • Shaft Vibration ◦ Sensor: Eddy current sensor (non-contact) ◦ Installation: Inside the bearing, in X and Y directions (at 45° to each other) ◦ Unit: μm (double amplitude/peak-to-peak) ◦ Features: Direct, sensitive, without transmission attenuation
• Wa Zhen ◦ Sensor: Speed sensor (contact type) ◦ Installation: Bearing housing/bearing cover (vertical or horizontal) ◦ Unit: mm/s (RMS value) ◦ Feature: Measures the support system and reflects the vibration after transmission
2. Problems reflected • High shaft vibration, low bearing vibration: rotor issues (imbalance, bending, oil film oscillation, rubbing) • High bearing vibration, low shaft vibration: loose foundation/bearing housing, cracks in the platform, poor support stiffness • High vibration in both cases: severe failure or complex problems
3. Standards and Protection (3000rpm units) • Shaft vibration (ISO 7919 / GB/T 11348) ◦ Good: ≤80μm ◦ Alarm: 125～160μm ◦ Tripping: 250～254μm
• Vibration (ISO 10816 / GB/T 6075) ◦ Good: ≤3.8mm/s ◦ Alarm: 7.5～9.3mm/s ◦ Shutdown: 11.2～11.8mm/s
III. General Usage (Industry Practices) • Shaft vibration: Primary means for protection and fault diagnosis ◦ Directly trigger ETS shutdown (in most plants) ◦ Monitor X/Y values, shaft trajectory, phase, and spectrum
• Vibration of bearings: Condition monitoring, auxiliary alarms, and verification support. ◦ Traditional older units rely mainly on vibration of bearings. ◦ New units: Alarms based on bearing vibration and shutdown triggered by shaft vibration are the main approaches
• Combined use: shaft vibration indicates the rotor, bearing vibration indicates the support; they verify each other to prevent false alarms
IV. Differences in protection methods among the three major turbine manufacturers (most critical) 1. Dongfang Steam Turbine Co., Ltd. • Axis vibration is used as the primary protection mechanism. • Measurement points: X/Y directional axis vibration (eddy current method) + vertical bearing vibration (velocity method). • Protection logic: ◦ Axis vibration alarm: 125μm ◦ Tripping due to axis vibration: 250μm (tripping occurs when either X or Y value exceeds this limit, with a typical delay of 3 seconds). • Bearing vibration: Used mainly for alarms; it generally does not trigger direct tripping