The goal of this research was to gather knowledge and to analyze the problem of excessive vibration level of Gas Turbine Generator (GTG) 100 MW system installed in cogeneration power plant in Sumatra Island, Indonesia which supports one of biggest oil and gas industries in Indonesia. The case research related to vibration problem were presented to diagnosis the main causes of excessive vibration that occur in the gas turbine generator during operation. Vibration analysis is one of the most important activities in predictive maintenance. Vibration monitoring system and machinery diagnostic technical specification are presented. The vibration data of this research were collected using online vibration monitoring system Bently Nevada 3500 series and system 1® display software at different bearing locations during transient (shutdown & start-up and steady state (on-line) condition. Assessment on overall vibration levels shall refer to Original Equipment Manufacturer (OEM) alert & danger set points, as well as relevant ISO 20816-2 standard. Finally, recommendation of reducing excessive vibration level is provided to ensure safe and reliable operation of the GTG unit.
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Journal of Physics: Conference Series
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Vibration Analysis For Reducing Excessive Vibration Level on Gas
Turbine Generator (GTG) 100 MW in Cogeneration Power Plant
To cite this article: Matsaid Budi Reksono and I Made Miasa 2019 J. Phys.: Conf. Ser. 1351 012083
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Journal of Physics: Conference Series 1351 (2019) 012083
IOP Publishing
doi:10.1088/1742-6596/1351/1/012083
1
Vibration Analysis For Reducing Excessive Vibration Level
on Gas Turbine Generator (GTG) 100 MW in Cogeneration
Power Plant
Matsaid Budi Reksono* and I Made Miasa
Department of Mechanical and Industry Engineering, Universitas Gadjah Mada, Jl .
Grafika No. 2, Yogyakarta, 55281, Indonesia.
*Corresponding author's email: matsaidbr@gmail.com
Abstract. The goal of this research was to gather knowledge and to analyze the problem of
excessive vibration level of Gas Turbine Generator (GTG) 100 MW system installed in
cogeneration power plant in Sumatra Island, Indonesia which supports one of biggest oil and
gas industries in Indonesia. The case research related to vibration problem were presented to
diagnosis the main causes of excessive vibration that occur in the gas turbine generator during
operation. Vibration analysis is one of the most important activities in predictive maintenance.
Vibration monitoring system and machinery diagnostic technical specification are presented .
The vibration data of this research were collected using online vibration monitoring system
Bently Nevada 3500 series and system 1® display software at different bearing locations during
transient (shutdown & start-up and steady state (on-line) condition. Assessment on overall
vibration levels shall refer to Original Equipment Manufacturer (OEM) alert & danger set
points, as well as relevant ISO 20816-2 standard. Finally, recommendation of reducing
excessive vibration level is provided to ensure safe and reliable operation of the GTG unit.
1. Introduction
Currently, the gas turbine & generator is the most versatile item of turbomachinery system. The gas
turbine is a power plant that produces a great amount of energy depending on its size and weight.
Industrial gas turbines can be used in several different modes in critical industries such us oil and gas
industries, process plants, aviation, marine, industrial mechanical drives and electrical power
generation [1].
The condition of a gas turbine generator (GTG) engine can be estimated by measuring the vibration
levels. As a system, GTG vibration is normally monitored by the plant's condition monitoring system
that serves as back up to its machine protection system. The vibration [2] is defined as any motion tha t
repeats itself after an interval of time. This motion can theoretically continue endlessly if there is no
damping in the system and no external effects (such as friction). The physical motion of rotating
machines generates vibration, which gives a physical indication of the health of equipment and the
generated vibration frequencies and magnitudes represent the machine vibration signature. Vibration
analysis is one of the most important in predictive maintenance, which is a powerful tool which allows
early detection of faults in rotating machinery. The malfunction of machines like unbalance, bent
shaft, misalignment, mechanical looseness, resonance, rotor rubs, journal bearings faults, electrical
faults, etc. can be determined in detail using vibration analysis [3].
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Machinery diagnostic application is an important concept required for effective machinery
malfunction diagnosis and determines root cause for machinery vibration problem. Analysis of phase,
vibration vector, fast Fourier transform (FFT), data plots like time base, average shaft centerline,
polar, bode, spectrum, etc. are discussed in detail [4].
In the field machinery vibration monitoring and analysis practices, a variety of relevant
measurement and standards for rotating equipment are developed and published by International
Organization for Standardization (ISO). Generally, assessment on overall vibration levels of gas
turbine generator shall refer to OEM alert & danger set points, as well as relevant ISO 20816-2
standard [5].
In this research, vibration analysis is carried out on one of three GTG machine trains, which consist
of SIEMENS SGT6-3000E gas turbine and BRUSH DAX air cooled generator with 100MW load
capacity and rotational speed 3600 RPM. This machine train has been experienced an excessive
vibration level reading. This excessive vibration values have been recorded at bearing #2 and bearing
#3 as shown in the vibration monitoring system. Analysis of this vibration behavior are required to
find out the remedial action to be done during next maintenance program.
The concept of vibration measurement in this machine is permanent monitoring, which is a system
whereby a set of instruments is continuously checking machine condition at a limited number of
measuring point [6]. Gas turbine generator vibration monitoring system, like other rotating
machineries, are usually equipped with some contact proximity probes, as vibration indicator. These
indicators are usually installed in main vibration monitoring tools. Both vibration data and trends are
captured and presented [7]. The vibration data were collected using online vibration monitoring
system Bently Nevada 3500 series and system 1® display software at different bearing locations
during transient (shutdown / start-up ) and steady state (on-line / full speed full load) condition. The
shaft relative vibration (XY non-contact proximity probes) and absolute vibration (seismic contact
probes) were installed on each of the GTG train's fluid-film bearings. Both vibration monitoring
systems equipped with alert and danger set point. The GTG is tripped in danger condition. The XY
pairs of non-contact proximity probes are mounted at 45-degrees left (Y-probes) and 45-degrees right
(X-probe), shown in figure 1.
Figure 1. Relative and absolute vibration probes installation diagram
2. Theory Approach
In general, in most power plants industries, rotating parts are key components to generate electric
power. The faults of rotating machinery may cause its machine performance degradation and entire
system failures or break downs. These conditions are directly related to plant maintenance cost and
even the level of safety. As part of condition – based maintenance, implementation of vibration signal
monitoring is one of important way to avoid and prevent plant system failures. The following
discussion explains about machinery fault types detected using vibration analysis as technical
reference of this research.
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Unbalance. Unbalance is the most common source of vibration in rotating equipment. However,
rotor with a vibration problem should not automatically be assumed to be out of balance. Vibration
spectrum can diagnose true machine unbalance condition. Vibration due to unbalance occurs at a
frequency of 1X shaft running speed of the unbalance element, and its amplitude is proportional to the
amount of unbalance. As explained and documented by [8] , the unbalance of rotating equipment has
unique characteristic in vibration spectrum or behavior of machine and can be characterized primarily
by one times (1X) shaft running speed.
Misalignment. The second major concern on malfunction of rotating equipment is misalignment.
One of study on rotor unbalance and shaft misalignment in rotating machinery has been conducted. In
order to understand the dynamic characteristics of these machinery faults, a model of a complete
motor flexible-coupling rotor system capable of describing these failures was developed. Generalized
system equations of motion for a rotor under misalignment and unbalance conditions were derived
using the finite element method [9]. In general condition, excessive misalignment typically produces a
large twice (2X) harmonic component of vibration and a high level of axial vibration [10].
Bent or bow rotor. The phenomenon of bends in rotor may be caused in several ways, i.e. due to
thermal distortion, creep or a previous large unbalance force. In general, when a bent rotor is
encountered, the vibration in the radial as well as in the axial will be high and the vibration spectrum
will normally have 1X and 2X component at slow roll speed. During thermal bow, rubbing will occur
between rotor and stator, causing a local hot spot and thermal expansion, there may be specific
symptoms will assist in the vibration diagnosis [11].
Rotor to Stator Rubs. Rotor to stator rub, can be one of the most damaging malfunctions of rotating
machinery. Rotor to stator rub is the event where rotating parts contact with stationary parts. Rotor to
stator rubs produce a vibration spectrum that similar with mechanical looseness. The rubbing may be
either partial or continues. R ubbing excites one or more natural frequencies of the shaft and
generates a series of frequencies to the spectrum that are integer fractions of sub-harmonics of the
running speed, for example 1/2X, 1/3X, etc. [1 2].
Cracked Rotor . Fatigue cracking is one important fault in rotating machines. The cracked rotor
vibration symptoms and the early diagnosis of cracked rotor can be detected mainly on two symptoms,
i.e. changes in 1X and/or 2X vibration vectors. Unexplained changes in the synchronous (1X) shaft
relative lateral vibration amplitude and/or phase at the operating speed and changes of the slow roll
vector on start-up and or shutdown. While the occurrence of twice the rotative speed (2X) vibration
component – occasionally at the operating speed, but especially on start- up and shutdown [13,14].
Mechanical looseness. Mechanical looseness in rotating machine, can normally occur at internal
assembly, machine to base plate interface, and machine structure. A looseness between the rotor –
supporting pedestal and the foundation is a common malfunction in rotating machines and usually
caused by the poor quality of installation or long period of impact vibration of the machine. High
harmonics are usually associated with mechanical looseness. The system with mechanical looseness
generally exhibits changes in the synchronous responses and an appearance of the 1/2X fractional
harmonic component and multiple harmonic component such as 2X, 3X, etc. [15].
Oil Whirl, oil whip and dry whip. O il whirl, oil whip and dry whip condition are several operational
problems with vibration of machines supported on journal bearings. These kinds of instabilities are
serious malfunctions in rotating machinery and may cause a machine catastrophic failure if they occur
simultaneously. Vibration due to journal bearings are complicated and have various characteristic. The
instability appears at sub-synchronous frequency of about slightly less than 1/2X, and close to 0.47X.
[16].
Electrical Faults. Vibration problem in generator, as part of gas turbine generator system, was
normally induced by electromagnetic forces in addition to the usual forces from mechanical effects
such as unbalance, misalignment, etc. This fault can be extremely frustrating and may lead to greatly
reduced reliability. However, this electrical malfunction on generator can be detected thru vibration
spectrum. In practice, the vibration spectrum or pattern emerging due to electrical problem on
generator will be at 1X shaft running speed and will thus appear similar unbalance. To do this,
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understanding the nature of vibration spectrum can assist in identifying the exact malfunction in
electrical machine [17,18].
Resonance. Resonance means a phenomenon that occurs when a periodic external force is applied
to a system having a natural frequency equal to the driving frequency. Resonance is also related to
critical speed. The excessive or high vibration amplitude at critical speed of the machine can be
catastrophic for any system and must be avoided at all costs [19].
Several studies related to excessive vibration on gas turbine phenomenon have been conducted, i.e.
study on dynamic behavior characteristic related to resonance and critical speed on gas turbine GE
MS3002 [20] and the phenomenon of high vibration in gas turbine 17.5 MW load capacity installed in
power and desalination plant [21].
The correction of common faults caused by vibration is required to ensure a safe and reliable
operation on machine. Field balancing, correct alignment and bearing inspection or repair are several
methods as action recommendation to solve vibration problems in rotating equipment [22,2 3].
3. Research Methodology
The research methods are explained and presented in this section. First , the main problem is defined
by determining and explaining in detail the problem occurred in cogeneration plant related to
excessive vibration level. The components that cause vibration within the machine must be identified.
The running speed of the machine, operation condition, and type of measurement that produce the FFT
spectrum are also included in this stage.
Second, several technical literatures related to this research are reviewed and used as technical
references. Third, perform a complete vibration data acquisition and processing. This includes
vibration data collection, process them in the vibration monitoring system, and record the results in a
form suitable storage system. Fourth, vibration data trending. In this stage, the trending and filtering
of vibration data during transient and steady state condition were carried out. Fifth, vibration data is
analysed to find out the main root cause of excessive vibration level. In this stage, analysis usually
follows a process of elimination which the components or issues that do not contribute to the system
are eliminated. The other remaining component which contributes in affecting the machine health shall
be identified. Then finally, provide a complete recommendation as remedial action to be conducted to
solve the problem of excessive vibration. The execution of remedial action shall follow the scheduled
site maintenance program.
4. Result and Discussion
This section presents research execution and full spectrum analysis of the vibration response. The
vibration data were retrieved on mid of June 2019 during GTG maintenance program (compressor
wash program) by covering two operational condition, i.e. transient (shutdown/start up) and steady
state (online 100 MW load capacity). From this data, an excessive vibration case history related to
GTG unit is analysed and discussed.
The excessive vibration level on GTG was found during full speed no load (FSNL) on bearing #2
gas turbine with 6.8 mils and bearing no#3 generator with value 7.4 mils. While vibration level during
steady state / full speed no load (FSFL) was detected at 6.0 mils on bearing #2 gas turbine and at 6.10
mils on bearing #3 generator. Both alert and danger set point on GTG unit are 5.7 mils and 8.6 mils,
respectively. These overall shaft vibration amplitudes values on both conditions were above alert limit
and zone C of ISO 20816-2. Hence, machines with vibration within this zone are normally considered
unsatisfactory for long-term continuous operation. In general, the machine may be operated for a
limited period in this condition until a suitable opportunity arises for remedial action.
Vibration level in transient condition should be focused because of the higher amplitudes. Figure 2
and figure 3 show bode plot of bearing #2 and bearing #3 on transient condition, i.e. from start-up to
full speed no load (FSNL). During this period, at the vibration value reached about 0.69 mils (bearing
#2) & 0.38 mils (bearing #3) at slow roll speed and going to 6,0 mils (bearing #2) and 6.10 mils
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(bearing #3) at operating speed (3600 rpm), The overall amplitude value is predominated by 1X
filtered amplitude and indicates that the rotor on unbalance condition.
Figure 2. Bode plot of bearing #2 on machine start up
Figure 3. Bode plot of bearing #3 on machine start up
In the same period as above, figure 4 and figure 5 illustrate the shaft relative vibration trends of
bearing #2 and bearing #3 during transient condition. The direct and 1x component vibration
amplitude trends of both bearing #2 and #3 indicated significant decrease and significant phase angle
changed.
Figure 4. Direct and 1X shaft relative vibration trend plot bearing #2
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Figure 5. Direct and 1X shaft relative vibration trend plot bearing #3
Figure 6, figure 7, figure 8, and figure 9 describe the direct (compensated) and 1X filtered orbit
plots on bearing #1 and bearing #4, within FSNL and FSFL condition, respectively. All plots
explained that significant orbit shape changed captured on bearing #1 and #4, large movement shaft
centreline on bearing #4 at FSNL as compared with FSFL, which were suspected as bearing and seals
clearance problem.
Figure 6. Orbit plot of bearing #1 (FSNL)
Figure 7. Orbit plot of bearing #1 (FSFL)
Figure 8. Orbit plot of bearing #4 (FSNL)
Figure 9. Orbit plot of bearing #4 (FSFL)
Figure 10, figure 11, figure 12, and figure 13 illustrate vibration amplitude changes of shaft relative
full spectrum on bearing #2 and bearing #3, respectively. On bearing #2 and bearing #3, vibration
amplitude changes of shaft relative full spectrum, and 1X vibration amplitude captured significant
which lead the bearing on unbalance condition.
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Figure 10 . Full spectrum plot of bearing #2
(FSNL)
Figure 11 . Full spectrum plot of bearing #2
(FSFL)
Figure 12. Full spectrum plot of bearing #3
(FSNL)
Figure 13. Full spectrum plot of bearing #3
(FSFL)
Figure 14 and figure 15 demonstrate the average (AVG) shaft centreline during start up to base
load period on both bearing #3 and bearing #4. From this plot , it suspected that rotor has experienced
an abnormal behaviour such as preload, probably rubs and also jacking oil system problem during this
period.
Figure 14. AVG shaft centreline plot bearing #3
Figure 15. AVG shaft centreline plot bearing #4
5. Conclusion
In this research, the main cause of excessive vibration on GTG unit is investigated in detail using
vibration analysis. Based on the result of analysis and a detailed evaluation of the acquired information
from the research, the following will be recommended solution in reducing excessive vibration with an
implementation plant for corrective action in the GTG unit machine.
(1) Perform lube oil analysis on bearing lube oil system to observe wear particle since clearance event
suspicious was detected on the bearing system.
(2) Propose to check clearance on bearing and seal #2, #3 and #4 and ensure that the bearing and seal
clearance are within tolerance prior running the GTG unit.
(3) In situ GTG rotor balancing as part of unbalance resolution on bearing #2 and bearing #3.
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References
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[3] Paresh G 2004 Practical Machinery Vibration Analysis & Predictive Maintenance First
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[5] International Standard Organization (ISO) 20816-2 2017 Mechanical Vibration – Measurement
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and Generators in Excess of 40 MW, with Fluid-Film Bearings and Rated Speeds of 1500
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Turbomachinery Symposium and Short Courses 129-139
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vibration response for oil whirl, oil whip and dry whip Mechanical Systems and Signal
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[17] Oliquino R Jr , Islam S and Eren H 2003 Effects of types of faults on generator vibration
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(UK: Athenaeum Press Ltd) p 159
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[23] Maurice L, Adams 2001 Rotating Machinery Vibration from Analysis to Troubleshooting
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-
![Krzysztof Lalik]()
- Filip Wątorek
The concept of predictive and preventive maintenance and constant monitoring of the technical condition of industrial machinery is currently being greatly improved by the development of artificial intelligence and deep learning algorithms in particular. The advancement of such methods can vastly improve the overall effectiveness and efficiency of systems designed for wear analysis and detection of vibrations that can indicate changes in the physical structure of the industrial components such as bearings, motor shafts, and housing, as well as other parts involved in rotary movement. Recently this concept was also adapted to the field of renewable energy and the automotive industry. The core of the presented prototype is an innovative interface interconnected with augmented reality (AR). The proposed integration of AR goggles allowed for constructing a platform that could acquire data used in rotary components technical evaluation and that could enable direct interaction with the user. The presented platform allows for the utilization of artificial intelligence to analyze vibrations generated by the rotary drive system to determine the technical condition of a wind turbine model monitored by an image processing system that measures frequencies generated by the machine.
Monitoring of rotating machines is very important task in most industrial sectors which requires a chosen number of performance indicators during the exploitation of these kind of equipments. Indeed for understanding the undesirable phenomena complexity of the industrial systems under operation, a reliable and a better accurate mathematical modeling is required to ensure the diagnosis and the control of these phenomena. This work proposes the development of a fault monitoring system of a gas turbine type GE MS 3002 based on vibration analysis technique using spectral analysis tools. The obtained results prove the effectiveness of the presented monitoring tool approach applied on the gas turbine, for avoiding the operation under vibration mode and for generating optimal performance during the exploitation of the gas turbine.
-
![Dr. V. Hariharan]()
Misalignment and unbalance is the most cause of machine vibration. An unbalanced rotor always cause more vibration and generates excessive force in the bearing area and reduces the life of the machine. Understanding and practicing the fundamentals of rotating shaft parameters is the first step in reducing unnecessary vibration, reducing maintenance costs and increasing machine uptime. In this paper, experimental studies were performed on a rotor dynamic test apparatus to predict the vibration spectrum for rotor unbalance. A self-designed simplified 3 pin type flexible coupling was used in the experiments. The rotor shaft accelerations were measured at four different speed using accelerometer and dual channel vibration analyzer (ADASH) under the balance (baseline) and unbalance conditions. The experimental and numerical (ANSYS) frequency spectra were also obtained for both base line and unbalanced condition under different unbalanced forces. The experimental predictions are in good agreement with the ANSYS results. Both the experimental and numerical (ANSYS) spectra show that unbalance can be characterized primarily by one times (1X) shaft running speed.
Oil whip induces self-excited vibration in fluid-handling machines and causes self-excited reverse precessional full annular rub, known as "dry whip", which is a secondary phenomenon resulting from a primary cause, that is, "coexistence of oil whip and dry whip". For predicting these instabilities, the clues are hidden in start-up vibration signals of these kinds of machines. This paper presents a method for predicting these kinds of instabilities. First, a Hilbert spectrum combining a full spectrum, which is named the "full Hilbert spectrum", is developed to reveal the whole process. Next, the transient position of a shaft centerline combining an acceptance region is introduced to predict instability at an early stage. The results presented in this study amply demonstrate the transition from stability to instability and the behavior of fluid-induced instability and rub in rotor systems. By this finding, bearing designers can completely understand these instability phenomena existing in fluid-handling machines. As a result, the control parameter for designing controllable bearings can be obtained and the instability problems can be resolved. Consequently, these findings are worth noting.
An experimental setup of rotor-bearing system is installed and vibration characteristics of the system with pedestal looseness are investigated. The pretightening bolt between the bearing house and pedestal is adjusted to simulate the pedestal looseness fault. The vibration waveforms, spectra and orbits are used to analyze the nonlinear response of the system with pedestal looseness. Different parameters, including speed, looseness gap, imbalance mass and disk position are changed to observe the nonlinear vibration characteristics. The experiments show that the system motion generally contains the 1/2X fractional harmonic component and multiple harmonic components such as 2X, 3X, etc. Under some special conditions, the pedestal looseness occurs intermittently, that is, occurs in some periods and doesn't in other periods.
Generators are frequently subjected to high currents and voltages caused by electrical disturbances in the power system. Faults in particular subject the generator to stresses beyond its design limits and cause high temperature increase, amplify and distort air gap torques, and create unbalanced flux densities. Even more stressful as a consequence of faults are sudden loss of load, fault clearance and reclosing.
- A. Sreenivasa Rao
- A.S. Sekhar
The shaft misalignment, even being a common fault in rotating machinery, is not sufficiently studied. The present work addresses effects of . misalignment in rotating machinery. An attempt to give a theoretical model for a rotor-coupling-bearing system has been done. The. rotor-bearing system including the flexible coupling is modelled using the finite elements. The reaction forces and moments developed due to flexible coupling misalignment both for parallel and angular are derived and introduced in the model. Vibration analyses such as eigen value analysis and unbalance response are carried out for the rotor system with misaligned shafts.
- Donald E. Bently
- Agnes Muszynska
The method of detection of rotor cracks by vibration monitoring is outlined. Various mechanisms stimulating cracks are discussed. Vibration measuring instrumentation and diagnostic methodology for early detection of rotor cracks are described.
Least squares balancing methods have been applied for many years to reduce vibration levels of turbomachinery. This approach yields an optimal configuration of balancing weights to reduce a given cost function. However, in many situations, the cost function is not well-defined by the problem, and a more interactive method of determining the effects of balance weight placement is desirable. An interactive balancing procedure is outlined and implemented in an Excel spreadsheet. The usefulness of this interactive approach is highlighted in balancing case studies of a GE LM5000 gas turbine and an industrial fan. In each case study, attention is given to practical aspects of balancing such as sensor placement and balancing limitations.
- M P Boyce
The Gas Turbine Engineering Handbook has been the standard for engineers involved in the design, selection, and operation of gas turbines. This revision includes new case histories, the latest techniques, and new designs to comply with recently passed legislation. By keeping the book up to date with new, emerging topics, Boyce ensures that this book will remain the standard and most widely used book in this field.The new Third Edition of the Gas Turbine Engineering Hand Book updates the book to cover the new generation of Advanced gas Turbines. It examines the benefit and some of the major problems that have been encountered by these new turbines. The book keeps abreast of the environmental changes and the industries answer to these new regulations. A new chapter on case histories has been added to enable the engineer in the field to keep abreast of problems that are being encountered and the solutions that have resulted in solving them.
Source: https://www.researchgate.net/publication/338014500_Vibration_Analysis_For_Reducing_Excessive_Vibration_Level_on_Gas_Turbine_Generator_GTG_100_MW_in_Cogeneration_Power_Plant
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