MagnaDrive Coupler Schematic

                                         Figure 1.  MagnaDrive Coupler Schematic 

                                          (Courtesy of MagnaDrive Corporation). 



Operation 

The MagnaDrive coupler is produced                   shaft.   A   copper   plated   assembly 

by    the   Seattle,    Washington-based             is attached to the motor shaft and 

MagnaDrive           Corporation.        The         as the motor turns, the load turns 

coupler       utilizes     the     attractive        with    only    a  2-3%     slip  when 

properties of rare earth Neodymium-                  operating      under     a   full   load 

Iron-Boron (NdFeB) magnets, which                    condition.      Since    no    physical 

do not consume electricity. Figure 1                 connection      exists   between     the 

illustrates    the  configuration     of  the        load   shaft   and   the  motor   shaft, 

coupler     whereby     the   magnets     are        the load can be gently applied to 

attached   to  a   rotor   assembly   located        the motor by adjusting the space 

on   the   load   side   of   operation.   This      between   the   magnetic   rotor   and 

assembly is  coupled  with        the  load          the copper plates. The amount of 



                                Irrigation Training & Research Center-www.itrc.org 


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                                                                   Adjustable Magnetic Coupler 

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



space        between         the      two 

assemblies         relates      to     the 

amount        of     slip.    Actuation 

components   regulate   the   space 

between       the  magnets      and   the 

copper plates.      Two double row 

bearings      rated   for   a   ten-year 

life   at   3600   rpm   support   these 

components         as    well    as   the 

magnetic rotor. 



Either   a   pneumatic   or   electric 

actuator     can    adjust   the   space 

between the magnetic rotor and 

the copper plates. The actuator 

may       be     controlled       by     a 

Programmable                       Logic 

Controller (PLC) with either a 4-20 mA, 1- 

                                                                     Figure 2.  MagnaDrive Installation 

5V   DC   or   a   0-10V   DC control   signal.        By         (Photo courtesy of Teichert Aggregates) 

slowly   applying   the   load   via   this   actuator, 

the amount of current inrush is significantly                        pump at Roza Irrigation District in Sunnyside, 

reduced,      thereby    extending     the   life  of  the           WA,       and     a   300    HP     pump      at   Teichert 

motor.        In     addition,      other      electrical            Aggregates   in   Sacramento,   CA.   Operators   at 

components within the system will not be as                          each location described their experiences. 

affected as there is not a large current draw 

upon start-up of the motor.                                                Table 1.  Facilities interviewed by ITRC (June, 

                                                                                                2001). 

Design                                                                       F ac ility         L o catio n          M o to r 

MagnaDrive   representatives   require   detailed                            O x n ard 

                                                                          W astew ater 

information on the setup of the motor.               Such 

                                                                            T rea tm en t                          5 0  H P  @ 

items   include   the   shaft   size,   motor   HP   and                       P lan t        O x n ard , C A      9 0 0  R P M 

motor       configuration.        Based       upon      this                   R o za 

information,   the   proper   size   of   the   coupler                     Irrig a tio n      S u n n y sid e,   1 5 0  H P  @ 

can       be      determined.         The       necessary                    D istrict             W A            1 7 6 0  R P M 

components         for   installation     are   built   and                  T e ic h e rt    S a cram en to ,     3 0 0  H P @ 

shipped,   ready   to   install.   The   time   required                   A g g reg ates           C A           1 4 3 0  R P M 



for    installation    may    vary    from    site  to  site 

depending upon the existing configuration.                           Oxnard Wastewater Treatment Plant, 

                                                                     Oxnard, CA 

Investigation                                                        John Carter, Project Manager 

The Irrigation Training and Research Center 

(ITRC)        at   California       Polytechnic       State          In the past, the water treatment plant has had 

University   located   the   MagnaDrive   at   three                 difficulties      with    electrical     harmonics       and 

locations   as   described   in   Table   1.   A   50   HP           utilization      of    Variable      Frequency       Drives 

vertical     centrifugal     pump      is   used    at   the         (VFDs) only seemed to amplify the problem. 

Oxnard      Wastewater         Treatment       Plant    in           Parts   for   an   existing   older   VFD   on   a   50   HP 

Oxnard,       a   150    HP    horizontal      centrifugal           pump           were        difficult        to       obtain. 



                                                         Irrigation Training & Research Center-www.itrc.org 


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



Not     only    was    the   pump      affected    by   the          based on the fluctuations in the system, which 

harmonics, but the VFD also created a lot of                         proved difficult.      The pump has a static lift of 

noise, augmented by the fact that the pump is                        139      feet   and     by   using     the    MagnaDrive 

in   an   enclosed     environment.       The   treatment            coupler,   could   be   responsive   to   the   demand. 

plant wanted to install a product that did not                       Modifications   to   the   motor   stand   (Figure   3), 

have   these   difficulties,   yet   was   still   able   to         motor       shaft,    and     babbit     bearings      were 

provide flexibility in flow rate.                                    necessary         for    the     installation      of     the 

                                                                     MagnaDrive   coupler.   The   primary   reason   for 

Since       the    pump       is   vertical      and     the         the modifications was due to the fact that the 

MagnaDrive          coupling     requires      additional            setup was over 50 years old. 

space on the shaft, the motor had to be 

raised   by   approximately   24"   from   the 

original   location.   The   motor   was   then 

attached to the motor stand with square 

tubing     for   structural    support.     Total 

installation     time    for  the   coupler    was 

approximately         3  ½   hours,    completed 

by    MagnaDrive         installers.    Only      ½ 

hour   of   the   total   installation   time   was 

required       to    calibrate     the    actuator 

completed        by   Mr.    Carter     from    the 

provided   instructions.       In   addition,   he 

remarked        that   performing       this   task 

would be much faster the second time, 

perhaps   taking   as   little   as   10   minutes. 

Removal          of     the      unit     requires 

approximately 2 hours. 



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

Monitored by a PLC, the motor is allowed to                                  (Photo courtesy of Roza I.D.). 

start   under   no   load   and   run   for   20   seconds. 

The      load     is    then     slowly     applied      by 

adjustment   of   the   actuator.      The   amount   of             Some       problems      did   occur    after   the   initial 

time     allotted   for   this  no   load   condition     is         installation. Due to the extreme heat generated 

based   on   the   size   of   the   load   and   also   the         by   the   rotation   of   the   coupler,   the   copper   on 

time     required     to  obtain    full  speed     of  the          the   rotor   had   melted   off.   This   meltdown   was 

motor.                                                               likely caused by water flowing back down the 

                                                                     pipe,     turning    the    coupler     in   the   opposite 

Roza Irrigation District,                                            direction      at  an    estimated     5000     rpm.    This 

Sunnyside, WA                                                        problem was corrected with the installation of 

Mark Barnett, Lead Engineer                                          a    check     valve    downstream        of   the    pump, 

                                                                     preventing the flow of water backwards. 

One       of     MagnaDrive’s          first    irrigation 

applications       was    at   Roza    I.D.    where     the         Four other efforts were necessary to complete 

coupler      was    installed  to    maintain     a  water           the     MagnaDrive          configuration.       Problems 

level in a weir box that fed grower turnouts.                        included faulty actuators, small shaft size, and 

In  the  past,  a    ditchtender  would         have     to          an unbalanced coupler. 

attempt to maintain the water level in the  box 



                                                         Irrigation Training & Research Center-www.itrc.org 


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                                                                  Adjustable Magnetic Coupler 

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



The   main   problem,   however,   seemed   to   be                  6   hours   (Figure   4).   This   amount   of   time   was 

correlated      with   the   size  of   the   load   shaft.          necessary       because,      upon     dismantling       the 

Representatives        from     MagnaDrive        decided            pump,   the   crew   discovered   that   the   impeller 

that by turning the coupler around so that the                       was     very    badly     worn     and    needed     to   be 

heavier   magnetic   rotor   rested   on   the   larger              replaced. 

diameter motor shaft, the associated vibration 

problems would be significantly reduced and 

possibly   disappear.   To   make   certain   of   this 

fact,   Chip    Corbin,     a  vibration    specialist    at 

Impact   Engineering,   was   asked   to   examine 

the setup.    Measurements were taken and Mr. 

Corbin concluded that the resonant frequency 

of   the   coupler   was   approximately   1450   rpm 

before   and   2300   rpm   after   the   switch   of   the 

rotor.     The     former     speed      gave    a    clear 

indication      of  why    the  motor     was   vibrating 

prior to reaching full speed.         The latter (2300 

rpm)     was    much    greater    than   the   operating 

speed   and   was   believed   to   pose   no   threat   to 

operation.     No other problems were observed 

after   this   switch   and   Mr.   Barnett   remarked 

that    he   appreciated      the   dedication     of   the 

MagnaDrive          representatives      to   fixing    the 

problem. 



Teichert Aggregates, 

Sacramento, CA 

Mike Hurley, Asst. Plant Manager 



Energy       efficiency      and     the    prospect     of               Figure 4.  MagnaDrive Installation at Teichert 

experimenting   with   a   new   technology   lured                          Aggregates.  (Photo courtesy of Teichert 

Teichert      Aggregates        to   the   MagnaDrive.                                      Aggregates). 



Before      the  coupler    was    installed,    the  flow           Following       complete      installation,    the   motor 

rate    at   the   facility    was    regulated      rather          was started with no load applied. Engaging the 

inefficiently      using     a   gate    valve.     Mike             actuator, the load was slowly increased on the 

worked       closely     with    John    Brain     of   the          motor, which is when the system experienced 

Sacramento        Municipal       Utilities   District    to         some      vibration.    In   order    to   eliminate     the 

find   a   product   that   would   meet   their   needs             vibration, the heavier magnetic rotor assembly 

and      be    energy     efficient.     The    company              was switched with the drive assembly, placing 

currently     uses    VFDs     in  other    areas   of  the          the   magnetic   rotor   on   the   larger   motor   shaft. 

plant,     but    experienced       problems      due     to         By installing the coupler in this fashion it was 

harmonic vibrations.                                                 believed, as in the case of Roza I.D., that the 

                                                                     vibrations   would   likely  disappear   because   of 

Representatives              from           MagnaDrive               the   change   of   the   resonant   frequency.   As   an 

determined that the 21.5” coupler model was                          added     measure,     the   base   of   the   motor    was 

required and were able to install the unit in                        built up so that any vibrations that may occur 



                                                        Irrigation Training & Research Center-www.itrc.org 


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would      not   be   amplified.    The    coupler    has 

worked   very   successfully   for   Teichert   after              equipment       and   installation    costs.   Both    cost 

these    modifications,      requiring     virtually    no         figures    are   based    on  an   existing    pump    and 

maintenance. As a safety precaution, an 1/8”                       motor. 

steel   plate   was   installed   over   the   coupler   to 

prevent     injury   from   entanglement.       A   small              Table 2.  Cost Comparison between MagnaDrive 

glass window was also incorporated into the                                           couplers and VFDs. 

plate so that a visual inspection can be made                                        Size of         Cost of      Est. Cost 

on    the  drive    at  any   time.   The   plate   does,             Facility    MagnaDrive      MagnaDrive       of VFD 

                                                                      Oxnard           14.5        $    20,000    $  25,000 

however,   cause   some   abstract   movement   of 

                                                                       Roza            16.5        $    35,000    $  50,000 

the air resulting in a slight whirring noise.                         Teichert         21.5        $    30,000    $  75,000 



Conservation and Efficiency                                        The   relative   cost   of   the   MagnaDrive   at   Roza 

• Energy efficiency is achieved since the                          ID was reported to be high due to the control 

     pump is operating at or near the optimum                      package selected. 

     pressure. 

• Soft start feature reduces the current                           Energy Savings 

     inrush.                                                       Teichert   Aggregates   in   conjunction   with   the 

• Improved flexibility of flow rate means                          Sacramento Municipal Utilities District, found 

     less spillage in cases where flow is routed                   that   the   energy   savings   from   one   year   nearly 

     back to the source.                                           paid     for  the   initial   capital   outlay    for   the 

                                                                   MagnaDrive   as   indicated   by   Table   3.        This 

Benefits                                                           equates     to   savings    of  over    24%    in  energy 

• Very little maintenance, primarily grease.                       consumption per year.         The data is based on a 

• Soft start, saving on the life of the motor.                     demand       of  236   kW    before    installation,    179 

                                                                   kW     after   installation    and    operation    of   the 

• Typically a smaller control panel is 

                                                                   pump 16 hours per day,  6 days per week, 48 

     required compared to a VFD. 

                                                                   weeks per year.       Such savings are site specific 

• Unaffected by power quality and 

                                                                   and   in   this   case   may   be   influenced   more   by 

     harmonic distortion. 

                                                                   the    impeller    change     than    the   switch    to  a 

• No physical damage, should the load stop 

                                                                   variable speed. 

     suddenly. 

• No wear except for the bearings and                                    Table 3.  Energy and Monetary Savings of the 

     actuator.                                                               MagnaDrive at Teichert Aggregates. 

• Laser alignment of the shafts is not                                                        Demand 

     typically required since the unit can                                                    (kW-hrs / 

     tolerate up to 0.030” misalignment.                                       Cost / kW        year)          Cost / Year 

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

Cost                                                                After      $     0.07        824,832     $     57,738.24 

The     total  costs   to   install  the   MagnaDrive               Total Savings                262,656     $     18,385.92 

coupler, including labor  and the actuator for 

the   systems   at   the   three   locations   described,          Certainly,         installations        that       require 

are illustrated in Table 2.        As a comparison,                recirculation of pumped water or partly closed 

ITRC estimated the total costs for a Variable                      valves to maintain a desired flow or pressure 

Frequency Drive to be installed on the same                        will    use   less  energy    with    a  variable    speed 

horsepower         motors        including      typical            pump.