Vibrations of Power Plant Machines - A Guide for Recognition of Problems and Troubleshooting

Preface

Contents

1 Basics of Vibrations

1.1 Kinematic of Vibrations

1.1.1 Periodic and Harmonic Vibration Signals in the Time Domain

1.1.2 Vibrations in the Time and Frequency Domain (Fourier Analysis)

1.1.3 Relations Between Deflections, Velocities and Accelerations

1.2 Vibrations of a Single Degree of Freedom (SDOF) System

1.2.1 Effect of Damping on Free Vibration

1.2.2 Effect of Damping on Forced Vibration

1.3 Vibrations of a Simple Rotating Shaft—The Laval Rotor

1.4 Rotors in Practice

2 Instrumentation and Measurement

2.1 Measuring and Analyzing Instruments

2.1.1 Velocity Transducers

2.1.2 Eddy Current Measuring Chain (Proximity Transducers)

2.1.3 Acceleration Sensors (Accelerometer)

2.2 Measuring Positions and Units

2.3 Visualization of Vibration Data

2.3.1 Time Trend

2.3.2 The Bode Plot

2.3.3 The Polar Plot

2.3.4 The Shaft Centerline Plot

2.3.5 The Orbit/Time-Base Plot

2.3.6 The Waterfall Spectrum Plots

3 Fault Analysis: Vibration Causes and Case Studies

3.1 Mass Unbalance

3.1.1 Rigid Rotors

3.1.2 Flexible Rotors

3.2 Thermal Unbalance

3.2.1 Example of a 120 MW Gas Turbine

3.2.2 Example of a 250 MW Gas Turbine

3.2.3 450 MW Combined Cycle Plant, Compromise Balancing

3.2.4 Instant Vibration Increase (Step Change)

3.3 Non-homogenous Rotor Material

3.4 80 MW Gas Turbine Starting Behavior

3.5 Magnetic Unbalance of a 20 MW Hydroplant in Switzerland

3.6 Instable (Non-repeatable) Unbalance

3.7 Structural Resonance Problems

3.7.1 200 MW Steam Turbine, the Netherlands

3.7.2 1300 MW Generator Test Run

3.7.3 700 MW Turbo-Set in a Power Plant in Scotland

3.8 Axial Vibrations

3.8.1 300 MW Turbo-Set in Switzerland

3.8.2 Combined Cycle Plant in Saudi Arabia

3.8.3 150 MW Steam Turbine at the Philippines

3.9 Structural Resonance Problems

3.9.1 Vertical Machines

3.9.2 Mechanical Looseness

3.10 Alignment Faults—Coupling Errors

3.10.1 100 MW Gas Turbine in Brazil

3.10.2 750 MW Generator in Former Yugoslavia

3.10.3 150 MW Generator in Spain

3.11 Rubbing

3.11.1 80 MW Steam Turbine

3.11.2 150 MW Steam Turbine

3.11.3 Spiral Vibrations—Rotating Vectors

3.11.4 750 MW Steam Turbine Generator

3.11.5 150 MW Generator Rotor in the Spin Pit

3.11.6 400 MW Single-Shaft Combined Cycle Plant in Chile

3.11.7 300 MW Steam Turbine Generator in China

3.11.8 General Conclusions of Vector Rotation—Spiral Vibrations

3.12 Development of 2X (Twice Rotation Frequency) Vibrations

3.12.1 Sag Excitation

3.12.2 Magnetic 2X Vibrations

3.13 Rotor Cracks

3.13.1 Considerations Regarding Lateral Cracks

3.13.2 4?×?930 MW Steam Turbine Plant, Lateral Crack

3.13.3 MW Steam Turbine, Lateral Crack

3.13.4 MW Combined Cycle Plant, Ring-Shaped Cracks

3.14 Bearing Instabilities: Oil Whip, Medium Flow Instabilities

3.14.1 Feed Water Pump, Oil Whip

3.14.2 50 MW, 60 Hz, Combined Cycle Plant, Friction Whirl

3.14.3 80 MW Air-Cooled Generator of a Gas Turbine

3.14.4 Small Steam Turbine, Rotor 760 kg, 12,000 rpm

3.14.5 Medium Flow Instability

3.14.6 135 MW Steam Turbine

3.14.7 Instable Compressor Air Flow, Rotating Stall

4 Jobsite Balancing

5 Vibration Limits

6 Some Hints to Identify Vibration Problems

References