מגבלות רטט — טורבינות גז

ISO 20816-4 covers all types of gas turbines used in power generation and mechanical drive:

• Industrial heavy-duty — Large frame machines typically >40 MW (e.g., GE Frame 7/9, Siemens SGT-800/2000)
• Aero-derivative — Derived from aircraft engines, typically 20–60 MW (e.g., GE LM2500/LM6000, Rolls-Royce Trent)
• Small gas turbines — Units below 3 MW including microturbines and small industrial drives

Strictly, the ISO standard itself addresses gas-turbine sets with fluid-film bearings; applying its guideline values to aero-derivative or small units with rolling-element bearings is a simplified non-ISO extension.

Bearing housing vibration is measured with sensors (accelerometers or velocimeters) mounted on the bearing pedestal. It provides overall machine vibration in mm/s RMS and is the most common measurement for protection and monitoring.

Shaft relative displacement is measured with proximity (eddy current) probes installed inside the bearing clearance. It measures the actual shaft orbit in μm peak-to-peak and is essential for detecting rotor dynamic issues that may not be visible on the bearing housing.

Gas turbines generally have higher allowable vibration limits due to:

• Combustion-induced vibration — a source not present in steam turbines
• Higher power density and different rotor dynamics
• Operating environment factors (thermal gradients, fuel variations)
• Different bearing and support configurations

For example, bearing housing velocity Zone A/B boundary is 4.5 mm/s for gas turbines (ISO 20816-4) vs. 2.8 mm/s for steam turbines (ISO 20816-2).

Aero-derivative gas turbines have unique characteristics:

• Multi-spool design — gas generator and power turbine rotate at different speeds
• Higher speeds — gas generator may run at 8000–15000+ RPM
• Rolling element bearings — some aero-derivatives use ball/roller bearings instead of journal bearings
• Lighter rotors — more responsive to unbalance and thermal effects

The zone boundaries in this calculator apply as general guidelines; always check OEM specifications for your specific machine.

A sudden vibration increase on a gas turbine requires immediate investigation:

• Check combustion dynamics — combustor issues can cause sudden vibration spikes
• Foreign object damage (FOD) — blade loss causes immediate unbalance
• Bearing deterioration — sudden change may indicate bearing failure
• Coupling problems — misalignment or coupling component failure
• Thermal transients — rapid load changes can cause temporary rotor bowing

Most gas turbines have automatic vibration trip systems. Never override or bypass vibration protection.