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Wireless technology

relessvibrationitoringna UScoal-

ary L. Gbur, Wane Wier and Torsten Barkoosing a reliable wireless system able to provide data on vibrationgnitudes in a coal pulverizer was never going to be easy, so two systemsalongsideeachother. .he Baldwin Energy Complexlocated close to Decartur, Illinois,- a coal-fired plant that generatesout 1761MW - was the site of a

nt-venture pilot project whiched to demonstrate a wirelessbration monitoring solution for aal pulverizer. The partners in theoject were the Electric Powersearch Institute and Dynegy, anganisation which providesectricity, natural gas, and natural gasuids to customers throughout theited States, and owns power plantsat cumulatively provide up toA versatile wireless solution wascided upon mainly because thests associated with installingnventional LAN cable or fibretics are higher.The objective was to identify aliable wireless system which was ableprovide overall vibrationagnitudes to Dynegy's OSI PIistorian at one-minute intervals. Theta collected by the PI data historianftware would eventually be routed tosplay monitors in the control roomprovide the operator with simplebration data values as well as alarmDynegy took a proactive approachmonitoring vibration levels onission-critical assets, focusing onrly detection and the notification ofnormal machine conditions. Thetimate goal was to enhanceuipment reliability and the safety ofA previously installed wireless pilotstem had failed to deliver reliableata and was taken out of service afterx months. However, Dynegy stillnsidered that a working solution forwireless vibration monitoring systemas the way forward. It selected twoew vendors for evaluation, one beingKF Reliability Systems. Bothendors' solutions w,ere employed

TECHNOLOGY Febrllary 2006

side-by-side, each system monitoringdifferent parts of the pulverizer.ApplicationA single CE-Raymond model 923 RPpulverizer equipped with eightWilcoxon 786A accelerometers - oneof six on the site - was chosen formonitoring. Accelerometers werepositioned on two motor sleevebearings, two worm screw rollingelement bearings, one bearing at the

Ceramic VenturiVaneLinerSpring

JournalFrameLiner-Accelerometer

Bearings

Figure 1: Sensor configuration on pulverizer

Dynegy's Baldwin Energy Complexbottom of the bull gear vertical shaft,and every grinding roll. Theaccelerometers were mounted on eachof three grinding roll journalassemblies. Figure 1.

In order to challenge the wirelesssolution, the pulverizer located thefurthest away from a wireless accesspoint (about 200 feet) was selected.Although this distance is acceptable inoffice environments it can be difficultin an industrial environment that haswalls, I-beams, pipes, and other metalstructures that serve as attenuatingobstacles for wireless signals. In thiscase, the wireless system needed to be

SeparatorTopLiner

Ceramic InnerCone InteriorLiner

InnerCone.- OuterLinerInnerConeSpoutLiner

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Wireless technologv

Figure 2: Accelerometer mountWear Sleeve OilSeals

Figure 3: Side view of the grinding roll showing the sensor locationable to transmit through a path thatincluded 5ft x 5ft metal air ductsconnected to each of the pulverizers.The typical indoor range of thewireless radios used was between 500ftand 1500ft and up to 16 miles outsidewith line-of-sight and high-gainantennas.

In addition to the wireless obstacles,the environment itself was subject toharsh conditions including seasonaltemperatures ranging from 40F to100F, fly ash, and water wash-downs.In addition, some monitoring pointswere looking at equipment runningspeeds of between 45rpm and 600rpm.

SKF system and half to the systemsupplied by the other vendor. Figures 2and 3.

Working from the sensors up, thetest began with machine conditiontransmitters (MCTs) measuringvelocity and enveloped acceleration. Ingeneral, these transmitters provide anindication of machine health, such asimbalance and misalignment;measurement of envelopedacceleration provides an indication ofbearing degradation.

Although only eight accelerometerswere employed ten MCTs were used.Two were doubled up, i.e., the systemwas delivered with the buffered outputfrom one channel (the raw accelerationsignal) serving as the input to anotherin two separate situations. This daisy-

SolutionDuring the pilot period, half of theaccelerometers were connected to the16

chaining of MCTs allowed additionalmulti-parameter measurements to bemade without the need to install moresensors. Figure 4.

All of the MCTs measuring velocitywere configured for a 1 inch persecond full-scale range; all of thosemeasuring enveloped vibration wereconfigured for a lOgE full-scale range.The MCTs provided a 4-20mAprocessed output that wasrepresentative of the overall channelvalue. By using a 16-channel analog todigital converter, the 4-20 mA signalscould be converted to ModBusEthernet (RS-485), and sent wirelesslyto the access point. The converter usedwas an RM 16Al, supplied by SKF'scustom products partner, STI.

Figure 4: initial measurements weretaken with a Microlog handheldvibration data collector and used todetermine the most effective types ofmachine condition transmitters (MCTs)for the application

The wireless transceiver selected forthe project was the OS2400-485Industrial Ethernet Radiomanufactured by Locus, (now calledRadioLinx). All of the devices wereDIN-Rail mounted and fitted into asmall, easy-to-mount enclosure. Thesystem was installed and made fullyoperational in one day.Discoveringhe failureFive days after installation thepulverizer experienced a bearingfailure on its number two grinding roll.The system was instrumental innotifying plant personnel that a changein the operating characteristics of thepulverizer had taken place. A review ofthe PI Historian showed thecorrelation between changes in

ENGINEERINGECHNOLOGYebruary2006

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pulverizer motor current and thevibration trends on the inboard motorbearing, outboard worm shaft bearing,and the number one and number threegrinding rolls prompting the predictivemaintenance engineer to take more in-depth vibration data with a portableanalyser.Motor current also was plottedalong with vibration data from thenumber one and the number threerolls. This data was obtained from the

SKF system. Even though the failuredid not occur within these rolls, thevibration from the failed roll wasstrong enough for the MCTs to detectit. Figures 5 and 6.The vibration data collected by thepredictive maintenance engineer,coupled with an unsuccessful attempt

to adjust the grinding roll, forced avisual inspection which revealed thatthe number two grinding roll bearinghad failed and that the roll haddropped into the bottom part of thegrinder and come into contact with thecone assembly.Both bearings in the roll had failedand disintegrated. The cause wassuspected as being a lack of oil in thejournal - which would contribute to therelatively rapid failure. The journalshaft was distorted due to the heat, andthe inner races of the bearing werestuck to the shaft. Furthermore, thebolts holding the upper journal housingto the grinding roll were sheared offcausing the grinding roll to slide andhit the centre feed pipe -breaking apiece out of it. Figures 7 and 8.

Fluctuation in Motor Current

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Increase in Vibration Observed on Motor InboardBearing and Worm Shaft Outboard Bearing

Figure 5: Plot showing the correlation between motor current and bearing-relatedvibration data

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Increase in VibrationObservedon Number 1 and Number 3 Rolls

Figure 6: Plot showing the correlation between motor current and the grinding rollvibration dataENGINEERINGTECHNOLOGYFebruary 2006

Figure 7: The failed bearings

Figure 8: The damaged centre feed pipeThe measurements taken from

grinding roll number two were beingfed into the non-SKF system but, eventhen, the MCT system detected ahigher vibration level. If the SKFsystem had been monitoring thisparticular channel it is believed thatthe enveloped readings would havedetected the fault earlier and wouldhave shown that a drastic change hadoccurred. It was thought likely that thiswould have been soon enough toprevent a catastrophic failure.After eight weeks of tests the SKFsystem (Wireless MCT-System) waschosen to provide the wirelessvibration monitoring solution. Theother system tested failed to providereliable and continuous service.

Gary Gbur, Wane Wier, and TorstenBark are with SKF ReliabilitySystems.Further information fromColin.Roberts@Skfcom

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