Free Engineering Tool #020
Vibration Limits — Steam Turbines & Generators >40 MW
Evaluate vibration severity for steam turbines and generators per ISO 20816-2. Supports bearing housing velocity and shaft relative displacement measurements.
Results
| Zone | Boundary | Description |
|---|
ISO 20816-2 Scope
ISO 20816-2 specifies vibration evaluation criteria for steam turbines and generators exceeding 40 MW output, operating at speeds between 1500 and 3600 RPM (50/60 Hz power generation). It covers both bearing housing vibration and shaft relative vibration.
Bearing Housing Vibration
Broadband vibration velocity is measured on the bearing housing (pedestal) in mm/s RMS, typically in the frequency range 10–1000 Hz. The boundary values below correspond to the published table column for shaft speeds of 1500 r/min and 1800 r/min; for 3000–3600 r/min machines the published boundaries are higher (A/B 3.8, B/C 7.5, C/D 11.8 mm/s RMS), so this simplified single table is conservative for 2-pole machines.
| Zone Boundary | Velocity (mm/s RMS) |
|---|---|
| A/B | 2.8 |
| B/C | 5.3 |
| C/D | 8.5 |
Shaft Relative Displacement
Shaft vibration is measured with proximity probes, expressed as peak-to-peak displacement in μm. These values are simplified for general application.
| Zone Boundary | Displacement (μm p-p) |
|---|---|
| A/B | 50 |
| B/C | 100 |
| C/D | 165 |
ℹ️ Note: Shaft displacement limits may vary with operating speed. The values above are simplified for general use. For exact speed-dependent limits, consult the full ISO 20816-2 standard.
⚠️ Important: Both bearing housing and shaft vibration should be monitored. A machine may show low bearing housing vibration but high shaft vibration, or vice versa. The worse of the two assessments governs the overall evaluation.
ISO 20816-2 applies to steam turbines and generators with power output greater than 40 MW, operating at speeds between 1500 and 3600 RPM (for 50/60 Hz power generation). This includes:
- Large power station turbine-generator sets
- Industrial steam turbines driving generators
- Combined-cycle plant steam turbines
- Nuclear power plant turbine-generators
Bearing housing vibration is measured with sensors mounted on the bearing pedestal, expressed in mm/s RMS. It reflects the vibration transmitted through the bearing to the support structure.
Shaft relative vibration is measured with proximity probes inside the bearing, expressed in μm peak-to-peak. It measures the actual shaft orbit relative to the bearing clearance.
Both measurements are essential — bearing housing vibration alone may miss internal rotor issues on stiff foundations.
Steam turbines use fluid-film (journal) bearings where the bearing housing may show low vibration even when the shaft has significant movement. Shaft relative measurement captures:
- Rotor unbalance and thermal bowing
- Oil whirl and oil whip instabilities
- Rotor cracks and rubs
- Misalignment between coupled rotors
Monitoring shaft vibration is critical for early detection of developing faults.
For Zone C on a steam turbine or generator:
- Immediately notify plant management and operations
- Investigate root cause — check balance condition, alignment, bearing condition, foundation, thermal state
- Increase monitoring frequency to continuous if not already
- Plan corrective action for the next available outage
- Monitor trend — if approaching Zone D, consider load reduction or planned shutdown
ISO 20816-2 consolidates the former ISO 10816-2 (bearing housing vibration) and ISO 7919-2 (shaft vibration) for steam turbines into a single unified standard. The zone boundaries are essentially the same, but the new standard provides updated guidance on combined evaluation using both measurement types.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional vibration analyzers and field balancing systems for turbomachinery. ISO 20816 compliant evaluation on-site. Used in 50+ countries.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
