Magna Drive

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Adjustable Magnetic Couplerhttp://www.itrc.org/reports/magnadrive/magnadrive.pdf ITRC Report No. R 01-005

EMERGING TECHNOLOGIES

Adjustable Magnetic Coupler

fficiency in termsof power

consumption is vitaland continues to beincreasingly important.The use of adjustablespeed pumps canreduce energyconsumption andimprove controllabilityof pressure or flows.One such technology,

the MagnaDrive

coupler, has beendeveloped for servicein a variety ofapplications.

OperationThe MagnaDrive coupler is producedby the Seattle, Washington-basedMagnaDrive Corporation. Thecoupler utilizes the attractiveproperties of rare earth Neodymium-Iron-Boron (NdFeB) magnets, whichdo not consume electricity. Figure 1illustrates the configuration of thecoupler whereby the magnets areattached to a rotor assembly locatedon the load side of operation. Thisassembly is coupled with the load

shaft. A copper plated assemblyis attached to the motor shaft andas the motor turns, the load turnswith only a 2-3% slip when

operating under a full loadcondition. Since no physicalconnection exists between theload shaft and the motor shaft,the load can be gently applied tothe motor by adjusting the spacebetween the magnetic rotor andthe copper plates. The amount of

E

Figure 1. MagnaDrive Coupler Schematic

(Courtesy of MagnaDrive Corporation).

Irrigation Training & Research Center-www.itrc.org


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space between the twoassemblies relates to theamount of slip. Actuationcomponents regulate the spacebetween the magnets and thecopper plates. Two double rowbearings rated for a ten-yearlife at 3600 rpm support thesecomponents as well as themagnetic rotor.

Either a pneumatic or electricactuator can adjust the spacebetween the magnetic rotor andthe copper plates. The actuatormay be controlled by aProgrammable LogicController (PLC) with either a 4-20 mA, 1-

5V DC or a 0-10V DC control signal. Byslowly applying the load via this actuator,the amount of current inrush is significantlyreduced, thereby extending the life of themotor. In addition, other electricalcomponents within the system will not be asaffected as there is not a large current drawupon start-up of the motor.

DesignMagnaDrive representatives require detailedinformation on the setup of the motor. Suchitems include the shaft size, motor HP andmotor configuration. Based upon thisinformation, the proper size of the couplercan be determined. The necessarycomponents for installation are built andshipped, ready to install. The time requiredfor installation may vary from site to sitedepending upon the existing configuration.

InvestigationThe Irrigation Training and Research Center(ITRC) at California Polytechnic StateUniversity located the MagnaDrive at threelocations as described in Table 1. A 50 HPvertical centrifugal pump is used at theOxnard Wastewater Treatment Plant inOxnard, a 150 HP horizontal centrifugal

Figure 2. MagnaDrive Installation(Photo courtesy of Teichert Aggregates)

pump at Roza Irrigation District in Sunnyside,WA, and a 300 HP pump at TeichertAggregates in Sacramento, CA. Operators ateach location described their experiences.

Table 1. Facilities interviewed by ITRC (June,

2001).

F ac ility L o ca tio n M o to r

O x n a r d

W a s te w a t e rTr e a t m e n t

P lan t O x n a rd , C A

5 0 H P @

9 0 0 R P M

R o z a

I r r iga t ion

Dis t r ic t

S u n n y s i d e ,

W A

1 5 0 H P @

1 7 6 0 R P M

Teicher t

A g g r e g a t e s

S a c r a m e n t o ,

C A

3 0 0 H P @

1 4 3 0 R P M

Oxnard Wastewater Treatment Plant,Oxnard, CAJohn Carter, Project Manager

In the past, the water treatment plant has haddifficulties with electrical harmonics andutilization of Variable Frequency Drives(VFDs) only seemed to amplify the problem.Parts for an existing older VFD on a 50 HPpump were difficult to obtain.


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Not only was the pump affected by theharmonics, but the VFD also created a lot ofnoise, augmented by the fact that the pump isin an enclosed environment. The treatmentplant wanted to install a product that did nothave these difficulties, yet was still able toprovide flexibility in flow rate.

Since the pump is vertical and theMagnaDrive coupling requires additionalspace on the shaft, the motor had to beraised by approximately 24" from theoriginal location. The motor was thenattached to the motor stand with squaretubing for structural support. Totalinstallation time for the coupler wasapproximately 3 hours, completedby MagnaDrive installers. Only

hour of the total installation time wasrequired to calibrate the actuatorcompleted by Mr. Carter from theprovided instructions. In addition, heremarked that performing this taskwould be much faster the second time,perhaps taking as little as 10 minutes.Removal of the unit requiresapproximately 2 hours.

Monitored by a PLC, the motor is allowed to

start under no load and run for 20 seconds.The load is then slowly applied byadjustment of the actuator. The amount oftime allotted for this no load condition isbased on the size of the load and also thetime required to obtain full speed of themotor.

Roza Irrigation District,Sunnyside, WAMark Barnett, Lead Engineer

One of MagnaDrives first irrigationapplications was at Roza I.D. where thecoupler was installed to maintain a waterlevel in a weir box that fed grower turnouts.In the past, a ditchtender would have toattempt to maintain the water level in the box

based on the fluctuations in the system, whichproved difficult. The pump has a static lift of139 feet and by using the MagnaDrivecoupler, could be responsive to the demand.Modifications to the motor stand (Figure 3),motor shaft, and babbit bearings werenecessary for the installation of theMagnaDrive coupler. The primary reason forthe modifications was due to the fact that thesetup was over 50 years old.

Figure 3. Motor Stand Modifications at Roza I.D.

(Photo courtesy of Roza I.D.).

Some problems did occur after the initialinstallation. Due to the extreme heat generatedby the rotation of the coupler, the copper onthe rotor had melted off. This meltdown waslikely caused by water flowing back down thepipe, turning the coupler in the oppositedirection at an estimated 5000 rpm. Thisproblem was corrected with the installation ofa check valve downstream of the pump,

preventing the flow of water backwards.

Four other efforts were necessary to completethe MagnaDrive configuration. Problemsincluded faulty actuators, small shaft size, andan unbalanced coupler.


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The main problem, however, seemed to becorrelated with the size of the load shaft.Representatives from MagnaDrive decidedthat by turning the coupler around so that theheavier magnetic rotor rested on the largerdiameter motor shaft, the associated vibrationproblems would be significantly reduced andpossibly disappear. To make certain of thisfact, Chip Corbin, a vibration specialist atImpact Engineering, was asked to examinethe setup. Measurements were taken and Mr.Corbin concluded that the resonant frequencyof the coupler was approximately 1450 rpmbefore and 2300 rpm after the switch of therotor. The former speed gave a clearindication of why the motor was vibratingprior to reaching full speed. The latter (2300

rpm) was much greater than the operatingspeed and was believed to pose no threat tooperation. No other problems were observedafter this switch and Mr. Barnett remarkedthat he appreciated the dedication of theMagnaDrive representatives to fixing theproblem.

Teichert Aggregates,Sacramento, CAMike Hurley, Asst. Plant Manager

Energy efficiency and the prospect ofexperimenting with a new technology luredTeichert Aggregates to the MagnaDrive.Before the coupler was installed, the flowrate at the facility was regulated ratherinefficiently using a gate valve. Mikeworked closely with John Brain of theSacramento Municipal Utilities District tofind a product that would meet their needsand be energy efficient. The company

currently uses VFDs in other areas of theplant, but experienced problems due toharmonic vibrations.

Representatives from MagnaDrivedetermined that the 21.5 coupler model wasrequired and were able to install the unit in

6 hours (Figure 4). This amount of time wasnecessary because, upon dismantling thepump, the crew discovered that the impellerwas very badly worn and needed to bereplaced.

Figure 4. MagnaDrive Installation at Teichert

Aggregates. (Photo courtesy of Teichert

Aggregates).

Following complete installation, the motorwas started with no load applied. Engaging theactuator, the load was slowly increased on themotor, which is when the system experiencedsome vibration. In order to eliminate thevibration, the heavier magnetic rotor assemblywas switched with the drive assembly, placing

the magnetic rotor on the larger motor shaft.By installing the coupler in this fashion it wasbelieved, as in the case of Roza I.D., that thevibrations would likely disappear because ofthe change of the resonant frequency. As anadded measure, the base of the motor wasbuilt up so that any vibrations that may occur


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would not be amplified. The coupler hasworked very successfully for Teichert afterthese modifications, requiring virtually nomaintenance. As a safety precaution, an 1/8steel plate was installed over the coupler toprevent injury from entanglement. A smallglass window was also incorporated into theplate so that a visual inspection can be madeon the drive at any time. The plate does,however, cause some abstract movement ofthe air resulting in a slight whirring noise.

Conservation and Efficiency Energy efficiency is achieved since the

pump is operating at or near the optimumpressure.

Soft start feature reduces the currentinrush.

Improved flexibility of flow rate meansless spillage in cases where flow is routedback to the source.

Benefits Very little maintenance, primarily grease.

Soft start, saving on the life of the motor.

Typically a smaller control panel isrequired compared to a VFD.

Unaffected by power quality andharmonic distortion.

No physical damage, should the load stopsuddenly.

No wear except for the bearings andactuator.

Laser alignment of the shafts is nottypically required since the unit cantolerate up to 0.030 misalignment.

CostThe total costs to install the MagnaDrivecoupler, including labor and the actuator forthe systems at the three locations described,are illustrated in Table 2. As a comparison,ITRC estimated the total costs for a VariableFrequency Drive to be installed on the samehorsepower motors including typical

equipment and installation costs. Both costfigures are based on an existing pump andmotor.

Table 2. Cost Comparison between MagnaDrive

couplers and VFDs.

Facility

Size of

MagnaDrive

Cost of

MagnaDrive

Est. Cost

of VFD

Oxnard 14.5 $ 20,000 25,000$

Roza 16.5 $ 35,000 50,000$

Teichert 21.5 $ 30,000 75,000$

The relative cost of the MagnaDrive at RozaID was reported to be high due to the controlpackage selected.

Energy SavingsTeichert Aggregates in conjunction with theSacramento Municipal Utilities District, foundthat the energy savings from one year nearlypaid for the initial capital outlay for theMagnaDrive as indicated by Table 3. Thisequates to savings of over 24% in energyconsumption per year. The data is based on ademand of 236 kW before installation, 179kW after installation and operation of thepump 16 hours per day, 6 days per week, 48

weeks per year. Such savings are site specificand in this case may be influenced more bythe impeller change than the switch to avariable speed.

Table 3. Energy and Monetary Savings of the

MagnaDrive at Teichert Aggregates.

Cost / kW

Demand

(kW-hrs /

year) Cost / Year

Before 0.07$ 1,087,488 76,124.16$

After 0.07$ 824,832 57,738.24$262,656 18,385.92$Total Savings

Certainly, installations that requirerecirculation of pumped water or partly closedvalves to maintain a desired flow or pressurewill use less energy with a variable speedpump.


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For Further Information

MagnaDrive Corporation1177 Fairview Avenue North Oxnard Wastewater Treatment PlantSeattle, WA 98109 6001 S. Perkins Street(206) 694-4700 Oxnard, CA 93033www.magnadrive.com John Carter

Instrument Technician Irrigation Training and (805) 271-2213

Research CenterCalifornia Polytechnic State University Energy-Water ConnectionSan Luis Obispo, CA. 93407 (916) 654-4070Dr. Charles Burt(805) [email protected] This information was developed by ITRC

under the PIER End Use Agricultural Sector

Program, administered by the CaliforniaEnergy Commission.www.itrc.org

California Energy CommissionRicardo Amon(916) 654-4019 DISCLAIMER: Reference to any specific

process, product, or service by manufacturer,trade name, trademark, or otherwise does notnecessarily imply endorsement orrecommendation of use by either CaliforniaPolytechnic State University, the Irrigation

Training and Research Center, the CaliforniaEnergy Commission, or any other partymentioned in this document. No party makesany warranty, express or implied, and assumesno legal liability or responsibility for theaccuracy or completeness of any apparatus,product, process, or data described previously.

[email protected]

Roza Irrigation DistrictP.O. Box 810Sunnyside, WA 98944

Mark BarnettEngineer(509) 837-5141

Sacramento Municipal Utilities District6301 S Street.Sacramento, CA 95817-1899John BrainEnergy Specialist II(916) 732-6667

Teichert Aggregates3500 American River DriveSacramento, CA 95864-5805Mike HurleyAsst. Plant Manager(916) 386-6873
http://www.magnadrive.com/http://www.magnadrive.com/http://www.magnadrive.com/mailto:[email protected]:[email protected]:[email protected]://www.itrc.org/http://www.itrc.org/mailto:[email protected]:[email protected]:[email protected]:[email protected]://www.itrc.org/mailto:[email protected]://www.magnadrive.com/


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Thisreportwas preparedaspartofCECContractNumber40099014.

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