Gas Turbine Introduction and Vibration Diagnostic Basics 2018/GT Intro and Vibration... · Lube Oil...

This document contains COMPANY CONFIDENTIAL and PROPRIETARY information of Mitsubishi Hitachi Power Systems Americas, Inc. (“MHPSA”). Neither this document, nor any information obtained therefrom is to be reproduced, transmitted or disclosed to any third party without first receiving the express written authorization of MHPSA.

Timothy S Irwin, P.E. – GTSE Service Engineering Manager

Gas Turbine Introduction and Vibration Diagnostic Basics

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Gas Turbine Introduction

Styles of Gas Turbines

Micro-turbines – typically produce tens to hundreds of kW. Some corporations advertise micro-turbines up to 1 MW, but that size of this style of machine is rare to date with most being in sizes less than 400 kW.

Aero-derivative gas turbines – Typically range in size from one MW to tens of MW. There is considerable use of this technology presently being used to improve performance efficiencies of larger ‘frame’ size gas turbines.

Large frame gas turbines – Typically range in size from just under 100MW to over 300 MW with current technology

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Today’s topic will be the large frame gas turbines

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Gas Turbine Introduction

5/19/2018 SL2 Slide 3

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Gas Turbine Basics – Major Sections

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Inlet Compressor Combustor

Turbine Exhaust

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Gas Turbine Basics – Structural Support

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Thrust & #2 Bearings

#1 Bearing

Compressor Support

Turbine Support

Exhaust Support

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Gas Turbine Basics – Bearing Support

Inlet Exhaust

5/19/2018 SL2 Slide 6

Radial Struts

Tangential Struts

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Gas Turbine Basics - Rotor

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Compressor Rotor 15 sections

12 through bolts

Turbine Rotor 5 sections

12 through bolts

Torque Tube Connects

Compressor to Turbine

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Gas Turbine Basics - Compressor

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Thrust Bearing

2 Pad - Tilt Pad Bearing

Inlet Guide Vanes

Blades

Vanes/ Diaphragm

Compressor to Torque Tube Connection

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Gas Turbine Basics – Combustor Section

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Basket

Nozzles

Transition Piece

Torque Tube

Air Bypass

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Gas Turbine Basics

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Bearing

Bearing Tunnel

Inner Diffuser

Outer Diffuser

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Gas Turbine Basics

5/19/2018 SL2 Slide 11

Know your bearings. Different bearings designs produce different operational characteristics.

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Gas Turbine Basics – Air and Fuel flows

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Inlet Air Fuel Exhaust/Hot Gas

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Gas Turbine Basics – Auxiliary Systems

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Lube Oil Rotor Cooling Air Pedestal Vacuum Seal Air

Bleed Air Vane Cooling Air

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Gas Turbine Basics

Characteristics of Gas Turbines Rotors

Rotor Flexibility

Will typically operate above the 2nd critical

Bearing supports – The connection from the bearings to the foundation are much more complex than other large turbo-machinery. This affects bearing foundation stiffness and thus rotor and machine operational characteristics

At 3600 rpm ‘Full Speed No Load’ a gas turbine is still near 2/3 of total power coming from the turbine end to drive the compressor. So even at full speed/no load these machines are not truly idling, and the operational data is meaningful. Although there is still thermal transient to go through during startup conditions that depending on insulation condition, ambient temperatures, etc. will still take many hours to stabilize. Foundations can take a full day or more to stabilize.

5/19/2018 SL2 Slide 14

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Forces on the machine

Forces that act on a machine

Internal influences – interaction with parts of itself

Support forces in bearings

Forces resulting from shaft deflection

Fluid dynamics and subsequent forces

External influences – forces that are applied to the rotor system

Axial Restraint – Rub

Casing distortion – Rub

Static radial loads - Rotor to rotor Misalignment

Unbalance – typically considered and handled as an external force

5/19/2018 SL2 Slide 15

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Rotor System Parameters

Stiffness

Damping

The equation below describes how displacement, force, and dynamic stiffness are related.

Displacement = Forces

Dynamic Stiffness

A change in displacement (vibration) is due to a change in the force applied or stiffness of the system. The equation below shows the relationship between frequency, stiffness, and mass.

𝐹𝑛 =1

2Π ×

5/19/2018 SL2 Slide 16

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Rotor System Parameters

Using the foundation of the previous information the following equation was developed to describe the motion of a shaft:

Rotor Equation of Motion (for fluid film bearings):

Fs +Ft +Fd +Fp =Mȑ

Spring stiffness + Tangential stiffness + Damping force + Pertubation force = mass x acceleration

−Kr + jDλΩr −Dṙ +mruω2ej(ωt+δ) = Mȑ

Reference: Fundamentals of Rotating Machinery Diagnostics – Charles T. Hatch & Donald E. Bently

5/19/2018 SL2 Slide 17

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Fault Conditions

Instrumentation Error

Unbalance

Misalignment

Rotor to rotor

Casing to rotor

Radial

Bearing Damage or excessive clearance

Rotor Bow

Looseness

Fluid Induced Instability

Shaft Crack

Resonance

5/19/2018 SL2 Slide 18

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Fault Conditions

Instrumentation Error

Loose connections – spikey signal

Failing sensor

Drift – change in scale factor

Improperly matched components – change in scale factor

Incorrect calibration – change in scale factor

Unbalance

Initial/Residual unbalance condition

Loss of balance weight

Loss of blade mass

Increase in blade mass

5/19/2018 SL2 Slide 19

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Fault Conditions

Misalignment

Rotor to rotor

Change in relative bearing position

Rotor to casing

Radial

Bearing Damage or excessive clearance

Babbitt damage

Tilt pad – tilting/rocking mechanism wear

Rotor Bow

Assembly issue

Thermal distortion (also known as thermal sensitivity)

5/19/2018 SL2 Slide 20

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Fault Conditions

Looseness

Bearing components

Bearing to pedestal

Pedestal to foundation

Rotor Components

Fluid Induced Instability

Bearing Whirl

Bearing Whip

Tilt pad flutter

Shaft Crack

Shaft stiffness change

Resonance

Is resonance itself a problem?

5/19/2018 SL2 Slide 21

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Data Acquisition for Machinery Diagnostics

Parameters

Bearing Temperatures

Operating conditions – Speed, MW, MVars, Blade path temps,

Lube oil system operating conditions - supply pressure and temperature, drain temperatures

Seismic vibration probes – velocity, accelerometer, velomitor

Relative vibration probes – note installation location/orientation

Transient and Steady State Data – vibration and operational parameters

5/19/2018 SL2 Slide 22

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Defining Terms

Steady State Conditions: The machinery is operating under steady conditions; steady load, speed, etc.

Transient Conditions: The machinery is operating under changing conditions; changing speeds (startup, coast down), changing loads

Static Data is any data that can be represented by a single number or status. Examples include vibration amplitude filtered vibration amplitude, filtered vibration phase lag, transducer gap voltage, etc.

Plot Examples: Tabular List, Trend, Spectrum

Dynamic Data is the actual vibration waveform. Sampling of the waveform and processing to provide both time domain (Orbit or Timebase plots ) and frequency domain (Spectrum plots). Dynamic data cannot be characterized by a single number.

Plot Examples – Bode, Polar, Shaft Centerline, Timebase, Orbits, Cascade, Waterfall

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Operating Conditions

Digital Control System (DCS) Data

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Target Operating Range Alarm/Trip SetPoints

Historical Operating Information

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Lube Oil System Operating Conditions

DCS Data

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DCS Data

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DCS Data

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DCS Data

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Tabular List

Vibration Data

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Note the different items available

Compare samples Look for slow roll stability

Compare data of different runs

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Trends

Vibration Data

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These are more advanced trends that apply not only overall but 1X amplitude and phase for

review and analysis

Blue trace – startup; black – loaded/steady state; red – coast down

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Trends – Gap Voltage

Vibration Data

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These are the raw gap voltages that are used to develop shaft

centerlines. Smooth movements are desirable. Anything else

could indicate a potential issue

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Trends

Vibration Data

5/19/2018 SL2 Slide 32

These are the raw gap voltages that are used to develop shaft

centerlines. Smooth movements are desirable. Anything else

could indicate a potential issue

These are abnormal plots

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Vibration Data

5/19/2018 SL2 Slide 33

Start-up and coast down comparison Amplitude shifts; phase shifts Overall and 1X amplitude and phase

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Vibration Data

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Start-up and coast down comparison Amplitude shifts; phase shifts Overall and 1X amplitude and phase Slow roll change due to a rub

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Vibration Data

5/19/2018 SL2 Slide 35

Uncompensated Compensated

Coast down comparison between compensated and uncompensated shows phase and amplitude shifts And peak critical speed shift

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Vibration Data

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Compensated data showing vibration signature differences between the two ends of the machine

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Vibration Data

5/19/2018 SL2 Slide 37

Steady state amplitude and phase shifts due to a rub

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Waveforms

Vibration Data

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Top two plots are slow roll noise levels for those channels Bottom two plots are uncompensated 3600 rpm data Same scales

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Waveforms

Vibration Data

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Compensated plots from previous slide show less than 0.5 mils of change in amplitudes

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Waveforms

Vibration Data

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Example of another machine with higher noise levels. Plots below are 3600 rpm

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Orbits

Vibration Data

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Example of a machine with preload on two of it’s bearings looking at the Direct Orbits. Left side plot with banana shape; right side plot with ‘flattened’ side.

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Orbits

Vibration Data

5/19/2018 SL2 Slide 42

Example of a machine showing the Direct Timebase and Orbit plots. Uneven travel through Timebase resulting in uneven elliptical shape

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Shaft Centerlines

Vibration Data

5/19/2018 SL2 Slide 43

Shaft Centerline plots of a startup and coast down on a large frame gas turbine. Left side plot is exhaust or #1 bearing; right side is compressor or #2 bearing. Abnormal movement of #1 bearing is due to thermal growth of the startup. During coast down, there was a horizontal preload indicated.

Coast down section of the data

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Shaft Centerlines

Vibration Data

5/19/2018 SL2 Slide 44

Shaft Centerline movements of a gas turbine that are more typical. Some horizontal preload, further evaluation of other data plots would be recommended

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Spectrums

Vibration Data

5/19/2018 SL2 Slide 45

Typical Spectral data for a Gas Turbine bearing and a Generator bearing. Generator bearing on right was indicating some sub-synchronous energy.

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Full Spectrum

Vibration Data

5/19/2018 SL2 Slide 46

Typical Full Spectrum data for a compressor bearing in a Gas Turbine. Some reverse precession energy indicated. Orbit plot would be elliptical

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Waterfall

Vibration Data

5/19/2018 SL2 Slide 47

Spectral plot shown during startup, loaded operation, and coast down. Lack of change in synchronous multiples during the speed transients indicated that this is ‘glitch’ in the signal and not actual vibration energy.

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Full Waterfall

Vibration Data

5/19/2018 SL2 Slide 48

Full Spectrum Waterfall shown (same data as previous slide) during startup, loaded operation, and coast down. Lack of change in synchronous multiples during the speed transients indicated that this is ‘glitch’ in the signal and not actual vibration energy.

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Cascade

Vibration Data

5/19/2018 SL2 Slide 49

Cascade plot (same data as previous slide) during startup, loaded operation, and coast down. Lack of change in synchronous multiples during the speed transients indicated that this is ‘glitch’ in the signal and not actual vibration energy.

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Full Cascade

Vibration Data

5/19/2018 SL2 Slide 50

Full Spectrum Cascade shown (same data as previous slide) during startup, loaded operation, and coast down. Lack of change in synchronous multiples during the speed transients indicated that this is ‘glitch’ in the signal and not actual vibration energy.

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Instrumentation Issues

Case Studies

5/19/2018 SL2 Slide 51

Proximity probe system

Velomitor Proximity probe in housing

Velocity Coil

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Case Studies

5/19/2018 SL2 Slide 52

Proximity Probe - Elevated Slow Roll amplitudes

• Mechanical Runout

• Electrical Runout

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Case Studies

5/19/2018 SL2 Slide 53

Wiring/Connection Noise

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Case Studies

5/19/2018 SL2 Slide 54

Good documentation layout for machine and instrumentation

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Case Studies

5/19/2018 SL2 Slide 55

Startup and initial loaded operation; clean 2nd critical; but some vertical preload as it reached full speed; #1 bearing

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Case Studies

5/19/2018 SL2 Slide 56

Startup and initial loaded operation; clean 2nd critical; but some vertical preload as it reached full speed - #2 bearing on the same machine.

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Case Studies

5/19/2018 SL2 Slide 57

Shaft Centerlines on the same machine during coast down. Rub on the #1 bearing was confirmed with the unusual shaft centerline movement.

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Case Studies

5/19/2018 SL2 Slide 58

Polar plots – Bearing 1 on the left; bearing 2 on the right during coast down. Shows 180 degree phase shift between ends at the 2nd critical.

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Case Studies

5/19/2018 SL2 Slide 59

Intermittent rub indication from trend data above. Amplitude increases occurred on an infrequent basis.

One amplitude increase was caught on dynamic data collection showing both amplitude swing and phase shifting

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Case Studies

5/19/2018 SL2 Slide 60

Tabular list used for slow roll data compensation selection and comparison between operational data points. Note all the different information that is available

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Case Studies

5/19/2018 SL2 Slide 61

Bode plots showing 1st and 2nd critical responses and increased response after 2nd critical

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W501F Example 3

Case Studies

5/19/2018 SL2 Slide 62

Polar plots showing 1st and 2nd critical responses and increased response after 2nd critical.

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Case Studies

5/19/2018 SL2 Slide 63

#1 bearing preloaded when compared to #2 bearing. Variation in Orbit shape from one revolution to the next would be good to do further investigation

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Case Studies

5/19/2018 SL2 Slide 64

#1 bearing horizontally preloaded when compared to #2 bearing.

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Case Studies

5/19/2018 SL2 Slide 65

Overall Vibration levels after a row 2 turbine blade replacement. Note blades were changed on turbine end, higher vibration incurred on compressor end.

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Case Studies

5/19/2018 SL2 Slide 66

Startup and coast down overall trend behavior after the row 2 turbine blade replacement

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Case Studies

5/19/2018 SL2 Slide 67

Coast down Polar plot behavior after the row 2 turbine blade replacement

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Case Studies

5/19/2018 SL2 Slide 68

Overall Vibration levels after balancing was performed by installing trim balance weights in the turbine end of the machine.

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Case Studies

5/19/2018 SL2 Slide 69

Startup and coast down overall trend behavior after trim balancing was performed by adding weights in the turbine end of the machine

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References & Bibliography

5/19/2018 SL2 Slide 70

References:

1. Fundamentals of Fluid Film Journal Bearing Operation and Modeling – Minhui

He & C. Hunter Cloud & James M. Byrne, Proceedings of the 34th

Turbomachinery Symposium 2005, Pages 155-176

2. Fundamentals of Rotating Machinery Diagnostics – Charles T. Hatch & Donald

E. Bently, Bently Pressurized Bearing Press

Bibliography:

• Gas Turbine Engineering Handbook – Meherwan P. Boyce, Elsevier Science

• V. Wowk, Machinery Vibration – Measurement and Analysis, McGraw-Hill

• ISO – 10816 – Mechanical Vibration

• ISO – 7919 – Mechanical Vibration

• API – 670 – Machinery Protection systems

• Metrix Machinery Diagnostic Services

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SL2 5/19/2018

Gas Turbine Introduction and Vibration Diagnostic Basics 2018/GT Intro and Vibration... · Lube Oil...

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