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VARAL L L V

AL M A AL MAY

by

Gunther H. eikert

gol ag

o asmssos, copoad

so, xas

Gunther H Peke receed hs degree n Mechancal Engneerng at theTechncal Unersty of Kaserslaute nWest Germany He joned oth n 1963and worked for fe years n the Research epartment for Hydrodynamclud Couplngs nce 196 he has assumed seeral nternatonal assgnmentsfor oth n rance pan and theUnted tates

Mr Pekert has been n Houston snce191 as the Regonal Manager for oth Transmssons the subsdary of oth' s Power Transmsson epartments

ABSTRACT

In the ast large cmressrs in the etrchemical industry were stly driven in ne f tw ways: by stea (r gas)turbines r by cnstant seed electrical mtrs. If the w fthe cmressr had t be cntrlled tw ways were ssible:t cntrl its seed r t cntrl its suctin. If w cntrl wasrequired the steam (r gas) turbine was the right answer sincein-lant stea culd be rduced at a rather lw cst (gas culdbe urchased fr an equally lw rice). In the case f mre

cntinuus even w rates the cnstant seed electric mtrwas a gd alternative. Fr startu the cmressr was byassed and if a certain cntrl was necessary suctin cntrlwas used withut even lking at the wer cnsumtin.Highly increased fuel cst esecially fr in-lant steam generatin has made cmmercially available electric wer frlarge generating lants mre attractive. On the ther hand frthe same reasn energy cnservatin makes seed cntrlmuch suerir t suctin cntrl and last but nt least themre diversied nature f feed stcks as well as mre uctuating rductin rates call mre en fr cmressrs t becntrlled. The same is valid fr ther centrgal machinessuch as biler feed water ums and ieline lading ums.

Tday mre and mre cmressrs are driven by variableseed devices ther than steam turbines. One way is t use

urely electric drives which are hwever still in the trialhase regarding large hrsewer. Anther much mrerven way is t use in cnnectin with a standard cnstantseed electric mtr a hydrdynamic s-called uid culing. The tye f uid culing mstly used fr this alicatin is the ne with integrated gears.

This kind f machine relatively new t the etrchemicalcmmunity has hwever rven its high reliability andavailability in thusands f alicatins in the wer generating industry mstly with biler feed ums. Other alicatins have included installatins in il rducing and shiinglants n latfrms shre and nshre and with ielineand lading ums. Successful cmressr alicatins g

59

back sme 15 years with numbers increasing ver the lastthree t fur years. These cmressr alicatins g u t10,000 h with utut seeds reaching 12,000 rm. Pumalicatins with many mre years f case histry exist u t30,000 h with designs available fr 60,000 h.

There are many mre alicatins f the hydrdynamicrincile in numerus ther industries in the frm f uidculings and trque cnverters as well as cmbined transmissins.

The intentin herein is t describe the hydrdynamicrincile and its technical alicatin in the fllwing areas

Basic nctin f hydrdynamic variable seed uidculings Advantages f using such culings Successl designs f such culings Tyical alicatins with centrigal machines Seed cntrl tins and instrumentatin Ecnmic advantages f seed cntrl Installatin and maintenance eliability and availability Other tyes f variable seed drivesThusands f variable seed uid culings in um and

cmressr alicatins wrldwide hve rven the high degree f availability the simle maintenance needs and the lnglife f such wear-ee machines

BASIC FUNCION O HYDRODNAMICVARIABLE SPEED FLUID COUPLINGS

The hydrdynamic rincile f wer transmissin wasdiscvered and develed by Prfessr Fettinger in the earlyart f this century. His basic idea was t integrate a um anda turbine bth centrigal in the same machine (Figure 1.The transmissin uid usually a mineral il is accelerated inthe um wheel and ges then ver int the turbine wheelwhere it is decelerated (Figure 2 In ther wrds in the umwheel als called the rimary wheel the mechanical energym the driver is cnverted int kinetic energy which in turnis recnverted int mechanical ener in the turbine wheelals called the secndary wheel nw turning the drivenmachine. The gemetrical frm f bth wheels as well as thefrm and distributi f the radial blades within these wheelsreects the knwledge and exerience f the manufacturer fhydraulic machines.

This rincile f hydrdynamic wer transmissins alies t all kinds f uid culings whether they are cnstantseed drain tye r variable seed tye. The rst gru ismstly used fr s starts verlad rtectin and gentleacceleratin. The secnd tye is als used t searate thedriven machine m the driver like a clutch withut lsingthe advantages f the rst gru.

The third gru variable seed uid culings is thesubject herein. In rder t btain the dierent seeds requiredagainst a given lad (i. e. the arabla f a centrigal um)

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6 PROCEEDNGS OF THE THRTEENTH TURBOMAHINERY SYMSIUM

Fiue 1 Foettine Pncipe.

Fiue 2 ydodynamic Powe Tansmission

the varible seed culing has t be adjusted in is lling s ast change its trque versus seed characteristic (Figure 3. Thisis basically dne by suerimsing an il w n the abvedescribed il circulatin between the rimary and the secnda wheels (Figure 4). In mst uid culings this is dne bysulying an il w, which can be cnstant fr smller units,but shuld be variable (deendent f the ccurring heat lad inthe culing) fr larger units, int the active art (bladed umand turbine wheel sectins) f the uid culing.

ntrl f the degree f lling is btained by intrductinf a variable verw, which is in this case a s-called sctube. he sc tube is a mre r less radially lcated tube

which has a curved ening directed against the diretin frtatin f the sinning il ring within the culing. It usuallyruns in a searate annular chamber, which is cnnected byaxial bres within the active art f the uid culing, andwhich will have the same il level, due t the centrigal frcein this wrking chamber

The sc tube is s designed and dinsined that itan, under all wrking cnditins, um ut mre il than thelling um can suly. By this trick, the seed variatincmes dwn t the simle, mechanical sitining f the sctube. A seed dierence between the um wheel and theturbine wheel always has t exist, in rder t create a circular

L

:d

SCP TUBE PSITIN

40

30

0 20 -

0

- UTPUT SPD

ure 3 Toqueeed Chaactestc of aiable peedluid Coupln.

Fiue 4. impe CutAway of a aiabe peed FuidCoupln.

il w between thse tw arts, by the dierence in thecentrigal frces, and s be able t transmit trque. he seedierence between the um wheel and the turbine wheel iscalled sli and is exressed in ercent f the um whel

seed. By inducing sli as the means f seed regulatin, slilsses are created within the freely circulating transmissin ilwhich in turn can be very easily transrted by this same lthrugh the sc tube, ut f the culin and int a heatexchanger. er dissiating its heat either t water r t air,the cled il ws back int the uid culing.

ADVANTAGES OF VARIABE SPEED COUPNGS

Lad-free startu f drier Stelessly adjustable startu as well as steless seed

regulatin

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VAIABL SPD FLUID COUPLIGS DIVIG

CTIFUGAL COMPSSOS AD OTHR CETRIFUGAL MACHINERY 61

Dmpening of torque peaks (and no harmonics) omeither side and thus,

ecreasing mechanical stress in the whole drive line Disconnecting driven mchine possible while driver

keeps running Torque limittion capabilities Wear-free power transmission Extreme high availability Low maintenance needs Very versatile regarding necessary accessories and in

strumentation, using standard models.

SUCCESSFUL DESIGNS OF SCH COUPLINGS

For the purposes here, the multitude of existing couplingsof these types can be divided into three asic families.

Varable peed lud ouplngs Wth Antrcton earngs

The dierent couplings with anti-iction bearings aremosly used for small and medium horsepowers in what cangenerally be referred to as industrial applications (Figure 5.These couplings exist in both the horizontal as well as thevertical versions. The simplest type has its rotating partssupported by the driving and driven shas. The other types areee stnding, lly enclosed, with the housing being either of

the barrel type or horizontally split. These couplings have amotor driven or mechanically driven oil pump, their scooptube is directly linked to a mechanical actutor, and the hot oilows into the sump. The oil cooler is normally located after theoil sump.

gure 5. arable peed Flud ouplng wth Ant-Frictionearngs 1) prmary wheel, 2) secondary wheel, 3) shell, 4)scoop tube housng, 5) ol sump, 6) ol pump, 7 scoop tube

Vaable peed lud ouplngs Wth leee earngs

Variable speed coupligs with sleeve bearings are used inthe power gnrating and petrochemical industries (Figure 6They also include both horizontal and vertical designs. Onetype is mostly used for low speed applications, and has basically the same features s the rst group. The second esign, forhigher speed (mostly with two pole motors), is typically drivingboiler feed pumps or ompressors.

Fige 6. Vaiabe Speed Fid oping wi Seeve Beaings1) prmary wheel, 2) secondary wheel, 3) shell, 4) couplnghousng, 5) scoop tube housng, 6) ol sump, 7) scoop tube, 8)ol pump, 9) auxlary ube pump.

This typeshows twonew features (Figure 7). The scoop

tube is no longer linked directly to the actutor, but to aninternal gear segment drive with a cam to be moved by theactuator. This roduces a linear behavior for theuid coupling,which means it can be adjusted in the plant to have a fllylinear response tothe input control signal. Theother feature isa regulating valvewhich is mechanically linked to the scooptube control This valve recirculates the working oil directlyback into the coupling, thus creating a closed circuit. In thiscase, the cooler is located aer the scoop tube. Theamount ofoilcirculationinthis closedcircuit is regulatedbythe valve as afunction of the occurring heat losses, thus providing an eventemperture level and lowering mechanical losses witn thesystem

Fgure 7. Varable peed Flud Couplngfor Two Pole ElecMotor Applcatos

Vaable peed lud ouplngs Wth Incoporate Gears

Variable speed uid couplings ith incorported gers arethe workhorses for higher horsepowers and/or speeds, andcombine variable speed couplings with sleeve bearings ithone or two steps of gear sets, all included in one housing(Figure 8) It was basically developd for boiler feedwaterpump applications, but has also been successlly used for

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62 PROCEEDINS OF THE THIRTEENTH TURBOACHINERY SYPOSIU

Fiue 8. ic Vibe Seed Geed Fuid i

ieline and lading ums fans cmressrs and very re

cently fr water inectin ums This tye f culing includes a hydraulic cylinder mving the sc tube thus allwing the use f smaller actuatrs and such additinal features asquick start r st Mre than 3,000 units f such drives mstf the in the 2,000 h t 30,000 h range are runningwrldwide with utut seeds between 900 rm (fans) and12,000 rm (cmressrs) The use f this variable seedgeared uid culing allws the use f simle standard tw rbetter yet fur le electric mtrs matchin mst any cmressr r um seed and results in a very cmact cstsavi soltio

e 9. Vbe Seed Geed Fuid i-Bic Deign 1) oil ump 2) auxiliar lube il um 3) mi ube ilpump 4) lube oil cooler 5) double filter 6) reure witchefor auxilia lube oil pum 7) exte ube oi f divigand/or driven machine ) wrkig oil pum 9) egultigvalve 10) working chamber (pum wheel+ tubie heel) 11)coop tube gvenor 12) coop tube itke 13) c tube 14)woking oil cer 15) hydulic clinde

A schematic f a sectin cut thrugh a standard geared

variable seed uid culing with ne ste u gear set at theinut side is shwn in Figure 9. The wrking il and the lubeil have searate systems bth using the same il ut f acmmn il sum The cmbined um set is mechanicallydriven m the inut sha

e wrking il ws m the centrigal lling umint the w cntrl valve m where it ges int the uidculing's active art t take care f the wer transmissinDuring this rcess its temerature increases The nw ht ilis remved thrugh the sc tube and umed thrugh theheat exchanger back t the w valve This sytem is a clsedcircuit where the lling um nly circulates il and maintainsressure The lube il um a sitive dislacement umbacked u by a mtr driven startu and standby um isuming il thrugh the lube il heat exchanger and duble

lter int the lube il system which als rvides if necessary external lube il fr the driver and the driven machinesIt als rvides the cntrl il fr the hydraulic cylindercntrlling the sc tube This design allws the use f smallcmact actuatrs which nly have t mve the air f camscntrlling the hydraulic gvernr istn as well as the wcntrl valve

Anther tye f variable seed uid culing (Figure 10includes tw dierent hydrdynamic circuits in ne systemtgether with the arriate gears t cver tw select arts fthe seed range with even higher eciency In this culingthe change m ne circit t the ther is dne in bthdirectins while running withut interrutin f the wer

Fie 10 Dube icui Vibe Seed Geed FuidCoulin

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64 PROCEEDINGS OF THE THIRTEENTH TURBOMACHINERY SYMPOSIUM

deending n the tanker's intake system and caacity Inadditin the uid culing als can be used t bring the umt a st with the main mtr running thus decreasing thenumber f starts fr large electric mtrs

SPEED CONROL OPIONS AND

ISRUMENAION

pee Control

Only fr sme very few simle alicatins is a manualcntrl via lever (with lcking device) r self-lcking handwheel sindle drive sucient fr seed cntrl The bulk findustrial and wer generatin alicatins need at least anelectrmechanical actuatr (neumatic actuatr tin fr theetrleum-related ndustry) with feedback fr sitin cntrlith additinal signalling cntacts and end sts tgther witha seed measuring and mnitring device Fr mre cmlexsituatins a sitining cntrller can als be sulied whichwill fllw a signal m the custmer's main cntrller Asadditinal features quick startu r st devices can be included in the seed cntrl

Instmentation

Standard instrumentati fr uid culings (Figure 13)includes il temerature and ressure instruments fr smallerunits and additinal bearing temerature thermeters andressure switches fr larger units as well as dieential ressure switches fr duble lters where alicable Fr mrestringent alicatins frequent tins are TDs r thermcules in all bearings and il lines vibratin and acceleratin rbes with the necessary accessries il level switchesand mre

Fire 13. Example of Instmentation for ariable peeFli Copling

Options

When secicatins are nt met by the standard unit thefllwing tins are available:

Gear arts meeting American Gear Manufacturers Assciatin (AGMA) and/r API 613 secicatins

Fluid culings withut their wn lube il systems canbe cnnected t cmmn il suly units which generally cnfrm t API 614 secicatins

If sace is restricted uid culings can utilize a at

sum with a searate il tank Sum heaters Duble heat exchanger systems with slenid valves Mirrr-image geared variable seed uid ulings fr

retrts

CONOMIC DVANAGE O PEED ONROL

In cmarisn with the still widely used thrttle cntrlsubstantil energy savings can be realized usig seed cntrlfr the drive f centrigal ums The smewhat higherinvestment ca be aid back with a relatively shrt term (net tw years) in mst cases Thrttle valves are als exsed thigh wear whereas seed cntrl diminishes wear in the umfr bvius reasns

In a very cnservative examle which was based n the

fllwing assumtins50 hurs at 100 ercent w

5,000 hurs at 89 ercent w2,800 hurs at 71 ercent w

the energy savings r seed cntrl versus thrttle cntrlcame t arximately ne hundred thusand dllars er yearnt seaking f reduced wear lwer nise levels and theradvantages f te use f variable seed uid culings Langand ees detail this examle

Fr cmressr dives variable seed culings have alsshwn substantial savings cmared with suctin cntrl rturbine drives In a recent case which has been erating frseveral mnths the cmlete cst f a retrt frm steamturbine t cnstant seed electric mtr-variable seed uidculing including cmletely new fundatins will be re

cvered within three years If an existing fundatin can bemdied the return time might be even lwer

INSALLATION AND MAINENANCE

During rst installatin the usual care has t be taken talign mtr uid culing and driver taking int cnsideratin the heat grwth m ambient t erating temeraturesNecessary ie cnnectins fr the cling system have t bemunted free f stress and be ickeled neutrlized andushed rir t cnnectin t the uid culing after nalalignment

Maintenance is mainly limited t the mnitring f instruments At indicated interals il levels have t be cntrlledand lters checked and changed ver and cleaned if necessaryer mre frequent checks intially il checks and eventual ilugrading r changing are limited t nce a year Eventuallythe existing grease rgrams f the actuatrs have t befllwed

RELIABILIY AND AVAILABILIY

Due t the wear-free wer transmissin and the absencef any cmlicated mechanical r eectrnic cmnents awell designed uid culing des rvide excellent reliabilityand availability Fr straight tye uid culings with antiictin bearings 361 units were bserved fr a erid f veyears A Mean Time Between Failures (MTBF) f 113,150

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VARIABE PEE FLUI COUPLIN RIVIN

CENTRIFUAL COPREOR AN OTHER CENRIFUAL MACHINERY 65

hours resulted from 2,828, 700 operating hours with 25 failuresIn a ptrochemical plant, three screw compresors are

drive with uch coupling Two of these units have runcontinuously since 1970, with loads beteen 75 percent and100 percent When the compresors are overhauled every 18months, the oil in the uid couplings is changed Over onehundred thousand hours have been accumulated without aneed to use the third (standby) unit

For 52 othe units using straight through uid coupling

with sleee bearings, two failures were obsered in the periodbetween 1968 and 1979 The calculated MTBF is 217,000hours

For the variable speed geared couplings, y-even unitswith powers between 11,500 kW and 20,000 kW have beenobserved Two failures were experienced in the time between1971 and 1979 The resulting MTBF is 273,600 hours Therepair of these failures was done in four days at ten hours foreach repair The average operating time of these units was 505years at the time of this study

OTHER TPES OF VARIABLE SPEED DRIVES

Hydrovicou drie system, oen mistakenly caled uidcouplings, have for very ndamental reasons a more complicated, and thus ess reliable, control mechanism Instead of

simpy positioning a scoop tube, they have to continuouslyhod a baance between the oil lm pressure in a rotating stackof clutch faces, and the couteracting clmping force Heat iscreated, ike in any other slip device (be it uid couplig orEddy current couping), but for this type of drive, heat isgenerated in a thi oil lm which ony theoretically may havean even heat distribution For obvious reason, al the oil owhas to be ltered, not ony the lube oil

Variable equency ytems, which have been frequentydiscussed in recent times, are still in reltively early developmet, at least for larger horsepower and speeds Their basicchracteristics are a ery simple-looking motor conguration,but rther arge quantities of highly ensitive and ot verymaintennce-free electronics These electroics need separate,protected and well-etilated locations, with a ltered airsppy

The torque of such drives is not always as mooth asgenerally required by connection couplings, gears and othermechanical compoents These drives cn cause tenencies tocrete harmonics, and can induce high torque peaks erflling out of synchronous running, as i the cae of a shortblackout which does not trip the unit To service such units,personnel with higher qualications and longer training arenecessary Until now, such drives did not gie the high availability gures indicated earlier for uid couplings

Variable equency systems are a ery interting alterative, and will probably get larger share of the variable speed

application in the ture, depending on the specic use andthe location of the drive Prospective engineers should not,however, only compare eciency numbres withot also takinginto conideration the initial cot and the reliabiity side

CONCLUSION

Variable peed geared hydrodynamic uid couplings, aproven means of peed variation, and with years of perfect casehistorie in thousands of applications with centrifugal

achines, have been successlly used to control the ow ofcentrigal compressors The reasons for this success are simpe nction and robust design, low maintenance needs, highreliability and availability at a very competitie system cot

BIBLIOGRAPH

Etner, S , "Hydrodynamic Variabe Speed Couplings inthe Petrochemical Industry, Voith-reprint 541e, VoithTurbo GmbH & o KG, raisheim, West Germany(1981)

Fechner, G, "Hydrodynamic Variable Speed ouping Technical Position, Typical Duties, R-536e, Voithprint, Voith Turbo BmbH & o KG, railheim, Wet

GermanyFechner, G and Lang, V, "Wear and Operating ost eduction of Slurry Pump by Meas of Hydrodynamic VariableSpeed oupling, ASME Winter Annual Meeting,ASME 80-WA/MH-3 (Noember 1980)

Gruschka, B, "Voith Variabe Speed ouplings as egulatingEquipment in Power Stations, Technsche Mttelungen,7th Ed, Voith-eprint -510e, Voith Turbo GmbH &o KG, railsheim, West Germany (1961)

Keller, , "Te Startup of Hydrodynamic oupings, -512e, Voith-reprint out of VDI-report No 73, Voith Turbo GmbH & o, KG, Heidenheim, Wet Germany(1963)

Lang, V ad ees, D, "Economic Advatages of Using

Variable Speed Fluid ouplings in Pump Drives, 7thTechnica onference of the British Pump Manufacturers'Association, Voith-reprint, -542e, Voith Turbo GmbH& o KG, railsheim, West Germany (1981)

appold, W, "Intallation of Variable Speed Geared ouplings as entrifugal ompresor Drives, Berlin, WestGermany (December 1983)

Wiegman, W, "Variable Frequency Drives Versu Hydrodynamic ouplings in Boiler Fed Pump Applications,Voith Transmiions, Allendale, New Jersey (November1982)

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66 PROEEDINGS OF THE THIRTEENTH TURBOMAHINERY SYMPOSIUM