Telediagnose_g_02 (Alignment of Turbine Generator)

1the condition monitoring magazine of PRFTECHNIK AG and Flender Service GmbH

Nr. 02 - September 2001

In this issue:Encouragement of trainees at PRF-TECHNIK AG & Flender Service GmbH

Application: A paper machine drivewith higher availability

Advantages of telediagnosis usingweb technology

Level 1: Measurement locations onstandard machines

Level 2: Basic rules for themeasurement of frequency spectra

Laser-optical alignment of a verticalturbine generator

News & trade fair dates

Condition monitoring application:

Paper machine drivewith a high degree of availabilityDr.Becker, N.Dahlhaus, Herne

Degree students and scientific traineesare being encouraged and challenged inthe future world of condition monitor-ing at both PRFTECHNIK and FlenderService. At Flender Service, a degreestudent has just completed his work onthe condition diagnosis of wind-drivengears, with particular consideration of

the planet stages. Measurements onwind force systems in Germany andHolland, on Flender test fields and withwind-driven gears from the retrofit pro-gram at Flender Service provided thefield tests which resulted in amazingresults. Continued on page 8.

The fourth gear failure of a papermachine! Teeth broken off, adjustingsprings thrown out, shafts cracked,wheel seats not holding up despitereinforcing measures. And a gear man-ufacturer who is no longer on themarket ... . the nightmare of any main-tenance engineer! And also the great-est risk to the companys own survival.Competent assistance is essential! Afterall, paper machines de-mand an availability of100 % wherever possible.The fact that measure-ments of sound conduct-ed through solids are notsufficient in this type ofsituation is covered in thefollowing report.

But one thing at a time.Mr. Remmelle, the engi-neer responsible for main-tenance in this paper fac-tory got in touch withFlender Service after thesecond gear failure witha feeling of foreboding to request support and areplacement gear for thebelt-driven intersectingpulp cutter. A replace-ment gear was designedby Flender Service andproduction began inHerne. Since failures oc-

curred again on the old gear in themeantime despite the jointly determinedreinforcing measures that were carriedout, the responsible design engineer atFlender Service, Mr. Schade, contactedhis colleagues at the Condition Monitor-ing department, to request a customervisit.

Figure 1 shows the gear that hadalready become increasingly noisy again

during the on-site visit. However, it wasnot just the noises alone that worriedMr. Remmelle, but the number of defec-tive parts. The adjusting springs of thebevel pinion drive shaft had beenknocked out, the adjusting spring flutehad partially broken away, individualteeth were completely broken off, shaftseats had become loose, the axle-drivebevel wheel was knocked out of its

PRFTECHNIK and FLENDER SERVICE

Joint encouragement of trainees

2The condition monitoring magazin

precision fit. This amount of damageclearly indicated that, not only noisesand vibrations, but also large forces arehaving an effect here. And the machineitself? The belt-driven intersecting pulpcutter runs more or less continuously.Depending on the quality of carton to beproduced, specific RPMs are set up andproduction runs day and night. Sincespecial papers are also produced, newfrequency converters were used in orderto increase the speed of production.Thus, RPM increases, e.g. from 600 m/min to 1600 m/min are nothing specialin the paper industry.

Still within the framework of the cus-tomer discussions, noise and vibrationmeasurements and, in particular, torquemetering were recommended and thenecessary preparations discussed. Asstrain gages and telemetry componentswould have to be installed on the rotat-ing shafts for mechanical torque meter-ing, a suitable date when the machinewould be at a standstill was immediatelylooked for. There were only a few hoursavailable in a single night from Sundayto Monday after all, there had alreadybeen too many unscheduled standstillsof the paper machine.

Yet this was no problem for the staff ofFlender Service condition monitoringdepartment. Figure 3 shows the part ofthe motor where the strain gages andthe telemetry components were in-stalled. The drive shaft up to the gearcan be seen on the right. Noise, vibra-tion and torque analyses were carriedout on the running paper machine andthe results were immediately analyzedon site. Figure 2 shows the frequencyanalysis of the gear noise with manyexcitations that were, however, still ac-ceptable for an emergency repaired gear.

But the measurement results in thetorsional moment signals were not sotypical. Figure 4 shows an example of ahigh resolution time plot of the torquewith the subsequent system standstill. Itfollowed from the measurements thatthe frequency converter continually at-tempted to compensate for the drive-shaft effect. As a result, there was con-stant acceleration and braking of theentire drive that, in some RPM ranges,even led to heavy alternating loads. Thecause of the damage had been found!Making the control device less sensitive

is not sufficient, as the whole controlsensitivity is required.

Lets replace the cardan shaft with aRUPEX coupling and we can place themotor nearer to the gear, was ourproposal that caused the worries of Mr.Remmelle, maintenance engineer at thethen Holfelder Packaging, to evaporate.

The replacement gear also orderedfrom Flender Service was no longer re-quired and is now running in anothersystem.

Figure 1:View of the ta-pered spur wheelgear of a gear man-ufacturer that nolonger exists

Figure 2: Frequency spectrum of thegear noise at 1500 rpm

Figure 4: Time plot with increased dynamic inthe torque curve

Figure 3:Torque measure-ments on a rotatingmotor shaft usingstrain gages andtelemetry


Mathias Luft, Roland Schhle, Franz Lebitsch

Telediagnosis enables innovativemaintenance and service concepts, forboth the operator and the manufacturerof machines and systems.

However, practical experience to datehas revealed that the telecommunicationitself frequently presents a bottleneckdue to technical problems or for reasonsof cost, which handicaps the introduc-tion of telemonitoring or telediagnosis.

Problems mainly arise as a result ofincompatible standards. Among otherthings, this can lead to telephone mo-dems not connecting or not functioningdue to incorrect bell voltages as themodem frequencies in the telephone sys-tem are suppressed.

The advent of the World Wide Weband its standards, accepted around theglobe, and percolating right down tomanufacturing areas, enables problem-free and economical telecommunica-tion. At the same time, the term WorldWide Web stands not only for the Inter-net, but also for Intranets, local net-works and field busses, provided thatthey are connected with one another bythe TCP/IP protocol.

The main advantages that result fromthe use of web technologies are:

Worldwide data transmission at localtariffs.

Significantly better transmission qual-ity than telephone modems.

Simple integration of web-capablesystems in existing networks.

Availability of favorably priced stan-dard components for setting up andextending TCP/IP-based networksthat also enable data transmission bymobile telephone, power supply net-works, fibre optics, telephone andISDN.

Short training periods because theweb technologies are generallyknown and accepted.

Platform-independence as browserand eMail programs are available forall current operating systems.

Sending alarms and plain textmessages by eMail, SMS or fax.

Prevention of software versionconflicts on user computers as the

Technology

Advantages of telediagnosis using web technology

application software is locat-ed on the web servers.

No requirement for specialsoftware on user computers standard browsers, eMailand FTP programs are suffi-cient.

Simultaneous access to a sin-gle web server by several us-ers.

On-site support by the Inter-net provider. The providerpersonnel speak the local languageand are specialists in all questions ofthe country-specific telecommunica-tion technology. They also providesupport for customary accountingrecords.

To take advantage of this enormousrange of benefits, we have developedour VIBRONET and GearController

online condition monitoring systems tobe able to use the web technology.

The systems now have an integratedweb server that can use the TCP/IP,HTTP, FTP and SMTP protocols. Theentire user software was converted toweb technology and is available in theform of dynamic HTML pages and Javaapplets on the web servers of the onlinesystems. The HTML pages form the userinterface of the system with graphicsthat can be freely designed to meetrequirements. Integrated machine

graphics show the user the inner work-ings of the aggregates to be monitoredas well as the sensor arrangement, animportant basis for an accurate machinediagnosis. Java applets integrated in theHTML pages visualize current alarmconditions and provide access to analy-sis functions and measurement data.When the system is connected, theHTML pages and Java applets are auto-matically loaded in the browser of theuser computer and executed there onthe so-called virtual machine. Conse-quently, version conflicts on user com-puters have become a thing of the past.

Our web-capable online systems havebeen frequently tried and tested in appli-cations around the world where theyhave proved that the consistent use ofweb technology offers great benefits andalso contributes to considerable savingsin communication costs.


4

Level 1Standard measurement locations

Condition Monitoring Grundlagen

The evaluation of the vibration severityand the rolling element bearing condi-tion of a machine requires measurementsto be carried out at suitable measure-ment locations. At the same time, thevibration severity is evaluated accordingto the maximum value of all recommend-ed measurement locations of a machine.According to ISO 10816-1, this requiresmeasured values to be recorded in thethree main directions to the shaft center

(vertical, horizontal and axial) at allbearing sites in the center of the bearing.The main vibration direction in machineswith horizontal shafts and rigid founda-tions is usually horizontal. In machineswith elastic foundations, this can also bevertical. Maximum values only occur axi-ally in special machines or in the case ofmachine problems. The maximum valueusually occurs on the bearing of theimpeller or on the coupling where thehighest dynamic forces occur. ISO13373-1 that was recently translated intoGerman describes detailed measurementlocations for different types of machine.It also includes the uniform designationof measurement locations that was takenover from the MIMOSA standard. Exam-ples of standard machines such as elec-tric motors or pumps are shown in thetwo figures.

To evaluate the condition of a rollingelement bearing, the measurement loca-tion should be selected in the loadedzone of the rolling element bearing. Therolling condition of a rolling elementbearing is evaluated according to thevibration accelerations that occurcounter to the direction of power trans-mission at the places where the so-

called lines of force are highest. Thismeans that the loaded zone of a motorwith a horizontal shaft usually lies be-tween the 4 and 8 o'clock positions on aclock-type scale. The static load of therotor supports itself downwards bysome rolling elements. In horizontalshafts with bearing cases, this meansselecting the measurement location at ahorizontal position somewhat below thejoint. For measurement locations onrolling element bearings, the distanceto the load range must be as short aspossible, with no additional joints be-tween them, and must not be measuredaround corners. This ensures a goodsignal level that is as high as possible,which is essential for valid measuredvalues. More detailed information onthis is given in VDI 3839 sheets 1 and 2and in VDI 3832 that is currently inpreparation.

Glossary oftechnical termsDid you know?

Internet, World Wide Web or WebThe World Wide Web is the global networkof all networks that are connected withone another by the TCP/IP protocol. It cov-ers the whole world and now pervades alllevels of communication, ranging frommachine control to the mainframe com-puter.

Internet providerThis is the provider of Internet accesses andservices. The provider realizes the transi-tion from the local telephone network tothe Internet itself.

TCP/IPTCP/IP is the abbreviation for TransmissionControl Protocol/ Internet Protocol, a num-ber of protocols originally developed bythe US ministry of defence to connectcomputers in different networks with oneanother. The TCP protocol is used to trans-port the data while the IP protocol takescare of the delivery.

Web serverA computer that administrates HTML pag-es, Java applets, application programs anddata stock and makes them available onthe computers connected via the web (cli-ents) on request. In our VIBRONET andGearController online systems, the webserver is an integrated component of thesystem itself.

HTML pagesHTML pages are document pages createdwith the HTML script programing language.One of the most important features ofHTML is inserting Hypertext links into adocument. Hypertext links allow anotherweb document to be loaded in the browserby simply clicking on the Hypertext link. Adocument can contain links to many otherdocuments that are connected with oneanother. These documents can be locatedon the same computer as the intial docu-ment, or on another computer on theother side of the world.

BrowserA browser is a client program for calling upand graphically displaying HTML pages. IfJava applets are contained in the HTMLpages, they will be handed over by thebrowser to the virtual machine and execut-ed there. The most frequently used brows-ers are the Netscape Navigator and Mi-crosoft Internet Explorer.

PreviewIn our 3rd issue you can read about:

CM application:High-speed gear service at a Danishcement factory

Level 1 Basic course:Further characteristic vibration values.

Level 2 Basic rules Part 3:Calculating typical excitation and in-terference frequencies

Technology: Digital and software-sup-ported tele service

Application: Measuring thermalgrowth on a low-temperature propanecompressor

Dieter Franke


Part 2:How to measure valid fre-quency spectra

When dealing with FFT spectra, thereis a danger of incorrect measurementsthat can result in diagnostic errors. Infact, almost all suppliers of frequencyanalyzers offer special training coursesand thick manuals. Still this does notprevent false measurements occurringvery frequently particularly in the caseof gear analyses as a result of insuffi-cient measurement technology. There-fore, our introductory course describessome useful standards and basic rules.You should pay attention to the follow-ing measurement settings in your mea-surements or on your service provider:

a) Adequatemeasurement periods

The effective measurement period isdecisive in the analysis of vibration sig-nals. If loads change, e.g. as in wind-powered systems as a result of gusts ofwind, measurement periods of up to 5minutes may be required for reproduc-ible measurements. For constant speedrotors and RPMs greater than 200 rpm,we recommend an effective measure-ment period of at least 10 seconds and,at RPMs greater than 20 rpm, a mea-surement period of at least 60 seconds.Because: a measurement period of 60seconds at 20 rpm means 20 revolutionsare the basis for the technical estimationof the rotating shaft vibration. Sincevery few analyzers allow the measure-ment period for measurements withinthe frequency range to be adjusted di-rectly, the number of averagings must beset high until the measurement periodsgiven above are reached.b) Frequency ranges that are

high enoughThe requirement for long measure-

ment periods and high frequency rangesplaces the highest demands on the fre-quency analyzer. For example, if two-channel vibrations up to 2000 Hz arerecorded for five minutes, 1 Mbyte ofmeasurement data are collected to beprocessed. Usually, the upper limits ofthe frequency range under considerationhave to be greater than the number of

Level 2Basic rules for measuring frequency spectra

Condition Monitoring Grundlagen

revolutions by a factor of approx. 100.Of course, alternatively, you can breakdown the frequency range into severalsections and carry out several measure-ments. However, this takes time.

c) Recommendedfrequency resolution

The analysis of sidebands is an impor-tant tool in machine diagnosis. For thesidebands to be adequately resolved, thenumber of lines must be corresponding-ly high. Thus, a frequency resolution of1600 lines is recommended for standardmachines, and 8200 lines for multiple-stage high-performance gears. Alterna-tively, you can break down the frequen-cy range to be analyzed into severalsmall sections again and perform severalmeasurements with a smaller line count.However, the time required increasesconsiderably.

d) Sufficiently highamplitude resolution

If individual frequency componentsare lost in the noise produced by themeasurement technology, the measure-ment technician misses out on informa-tion. On cooling tower drives, for exam-ple, strong winds can cause vibrations ofup to 15 mm/s, while the actual gearvibrations in the final gear drive stageare 0.015 mm/s, i.e. 60 dB weaker.

Therefore, the measuring system shouldhave a significantly higher dynamic re-sponse (e.g. 100 dB amplitude resolu-tion). Alternatively, you can attempt tofind ranges where the interference vi-brations do not occur so strongly, orwhere the specific gear vibrations arehigher, by using more measurement lo-cations. However, this also increases themeasurement overhead.

e) Correct window functionHarmonic and square-wave vibrations

must be evaluated differently in FFTfrequency analysis. Information is lost ifthe correct window functions for theFFT algorithm are not used. Just as inthe case of music with the introductionof the CD, digital filters can be betteradapted to the specifics and give betterresults. We recommend using a Hanningfilter as the window function, and not tochange this as far as possible.

A prerequisite of every good frequencyanalysis is that you know the kinematicsand the excitation frequencies of themachine before beginning the measure-ments. How to calculate rotating fre-quencies, blade frequencies, wobble fre-quencies, mesh frequencies, etc. will beexplained in the next issue.

Dr.Becker

Effect of presettings on the frequency analysis of a wind-driven gear

8200 lines4-second measurement timeSquare window

500 lines64-second measurement timeHanning window



Optimum Measurement periodtoo short

Resolution too low Amplitudes very small


1

2

A vertical 40 MW pumped storage in apumped storage plant attracted atten-tion as a result of unduly high shaftvibrations. From the vibration spectrum,the operator suspected the cause to beshaft misalignment between the turbineand pump. If this suspicion was correctthe shaft alignment needed to bechecked and corrected as necessary.

Due to the high level of accuracyrequired, vertical alignment of aggre-gates this type and size is very compli-cated. Measuring the actual conditionfor such aggregates is extremely timeconsuming as the coupling flange be-tween the turbine and pump can only beaccessed after dismantling the fixed gearcoupling and the starting turbine. Forprecise measurement, the following fac-tors must be taken into account. The turbine and pump rotors can only

be turned with the assistance of hy-drostatic lubrication on the thrustbearing and by means of turningmechanisms.

As the turbine and pump are uncou-pled, several people must operate theturning mechanisms in coordination(a team at the top on the generatorthat is coupled with the turbine, and asecond team at the pump).

The distance of 983 mm between thetwo coupling flanges is very large

The turbine and pump must be turned

synchronously to measurementpositions of exactly 90, al-though both rotors are uncou-pled. To avoid an eccentric rotorposition due to design relatedradial play, the pump rotor andturbine rotor must be centeredusing shim plates after eachnew turn of the radial bearings. If possible, the shaft align-ment should be corrected in asingle step as moving the radialbearings requires a considerableamount of manpower and time.The period available for theshutdown of the generating unitis limited.Under these constrictive condi-tions, measurement using con-ventional methods is almost im-

possible. For these reasons, the operatorelected to use a modern laser-opticalshaft alignment system for this criticaltask. ROTALIGN PRO shaft alignmentsystem with its integrated function forvertical alignmentis ideally suitedfor measurementsof this type.

The couplingwas opened with-in the scope of ascheduled inspec-tion. First, thecurrent conditionof the shaft align-ment had to bedetermined toconfirm the suspi-cion of the opera-tor.

The turbine wasthe stationary ref-erence machine.To achieve thegreatest possiblemeasuring accu-racy, the RO-TALIGN PROemitter was fixedwith a stable mag-netic jig on theaxial surface ofthe turbine cou-

pling and the ROTALIGN PRO receiveropposite on the coupling flange of thepump. The measurement could now be-gin.

The problem of the synchronous posi-tioning of the turbine and pump can besolved in a very simple way with a laser-optical system, as the laser beam can beused to project the rotary position of theturbine downwards onto the couplingflange of the pump. Conventionally, ad-ditional and specially adapted pointerrods would have to be attached for this.

Measurements were carried out atfour positions using the single pointmode. The adjustable averaging time ofthe ROTALIGN PRO sensor enables theelimination of interfering vibrations byother aggregates and ensures the high-est measuring precision. The pump rotorwas then rotated to the next 90 posi-tion. The turbine rotor being synchro-nously readjusted and the measured val-ues were recorded again. The pump andturbine rotors were centered preciselybeforehand with 4 shim plates in

Uwe Geyer (VEAG Pumpspeicherwerke, Hohenwarte), Mathias Luft (PRFTECHNIK AG)

Francis turbine

Lower radial bearing

Coupling flange turbine

Switchable coupling

Peltonpony turbine

Coupling flange pump

Upper radial bearing

Francis pump(2 stages)

Lower radial bearing

Axial bearing

Anwendung

Laser-optical alignment of a vertical pumped storage


3

4

5

each of the radial bearings.After approximately 3 hours, the re-

sult was determined. The shaft align-ment had a radial displacement of 1.54mm and 1.44 mm in the two perpendic-ular measurement directions respective-ly. These measurements lay outside theapproved tolerances by a factor of 10.The vector sum of these two displace-ments would result in the largest shaftdisplacement of 2.11 mm (!) somewhatbelow 45 degrees to these two mainaxes. This was revealed as a major causefor the increased vibration values.

Following computation of the aboveresults adjustment was to be carried outto correct the misalignment. The conver-sion of the coupling values resulted innecessary displacements of 1.54 mmand 0.67 mm respectively for the upperpump bearing, and 1.54 mm and 1.52mm respectively for the lower pumpbearing. This type of change in the rotorbearing also necessitates checking theclearance between the impellers and thecasing of the two-stage storage pump. Inthis application a similar displacementof parts of the casing was necessary torestore the concentric impeller clear-ance.

16 hours later, on the morning of thefollowing day, the control measurementcould be made. Tension was high. Hadthe nightshift worked well enough tomove the parts that weighed severaltons precisely to fractions of a millime-ter?

If a second correction had been re-quired, this would have overrun theschedule time for the inspection. In the

The figures show:

1. Machine room with 8 verticalpumped storages power stations

2. Assembly of the turbine pump

3. The Pelton starting turbine is dis-mantled which allowed the couplingflange of the Francis turbine (top)and Francis pump (bottom) to beaccessed.

4. ROTALIGN alignment system- ROTALIGN laser on the top of

coupling flange of the Francis tur-bine

- ROTALIGN sensor on the bottomof the coupling flange of theFrancis pump.

5. Log of the actual measurement.

afternoon, after final measure-ments were recorded in the lastmeasurement position, relievedfaces all round! The radial dis-placement in the two perpendicu-lar directions was now only 0.03mm and 0.22 mm respectively andwas, thus, reduced to a tenth ofthe starting value in a single ad-justment. An excellent result giventhe numerous influencing factorsthat can affect the accuracy of thisapplication.

After the generator was re-turned to service, the shaft vibra-tions were checked. They hadsunk to normal permissible values a complete success for both theoperator and for ROTALIGN PRO.


NewsGearController data collec-tor with network connection

GearController data collectors weredeveloped for portable measurement ap-plications where the service engineer orservice technician and not the diagnos-tician records the measurement re-sults, then reads them out and transmitsthe measurement results to the diagnos-tician as a file by eMail. In exactly thesame way, it is possible for companyworkers to collect measurement resultsindependently and then transmit theresults via the network. The world firsthere is that the network connection isrealized by the web server contained inthe GearController.

The GearController is enclosed in acarrying case and can store approxi-mately 300 spectra with a file size of33 kB. The data can be further processedby the OMNITREND PC software.

The exceptional service offer of Flend-er Service includes the preparation ofmeasurement routes and initial analysisin the form of annual contracts. In par-ticular, in the case of paper machinesand cooling tower drives, they haveextensive experience.

Continued from page 1:Joint encouragement

of traineesAnother degree student at

PRFTECHNIK AG is currently testingdiagnostic methods such as Cepstralanalysis, time averaging and short-termFFTs, both on the rotor seat and onstandard and wind-driven systems, andto integrate them in our hardware andsoftware as standard methods. Natural-ly, the initial tests and applications arealso being carried out on Flender gearswithin the framework of our partnershipand underlines the strength of a ventureof this type. We will also welcome train-ees and degree students in the future.

VIBSCANNER now alsoavailable with Ex protection

VIBSCANNER - the user-friendly datacollector and machine analyzer - cannow also be used in hazardous industrialenvironments (e.g. refineries, chemicalindustry, drilling rigs). The EX-proof (in-trinsically safe) version immediately ful-fills the protection class:EEx em ib IIC T4: TV 01 ATEX 1699.

PULLALIGN:Align belt pulleys with laser

Just call us: We will make you an offeryou cant refuse.

Flender ServiceWindtech Husum 18. - 22.09.2001Halle 4 Stand A418

USA: 30th Turbomachinery Symposium17. - 20.09.2001 in Houston, Lecture 11

PRFTECHNIK AGMaintenance 2001: Salon de toutes lesmaintenancesParis Expo Porte de Versailles du 20 au22 Novembre.

NEW

EventsTrade fairs and exhibits:

PRFTECHNIK AGPostfach 12 6385730 Ismaning, Germanywww.pruftechnik.comPhone: +49 (0)89-99616-0Fax: +49 (0)89-99616-200eMail: [email protected]

Flender Service GmbHCondition MonitoringSdstrasse 11144623 Herne, Germanywww.flender-cm.comPhone: +49 (0)2323-940-220Fax: +49 (0)2323-940-229e-Mail: [email protected]

Documents

Telediagnose_g_02 (Alignment of Turbine Generator)