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Thread: Downhill Motor Power Selection

  1. #1
    Join Date
    Jul 03
    Posts
    2

    Could you help?

    If I know the minimum minus shaft power of a declined conveyor
    ( for example -60kw), how should i select the motor power?

    Thank you for your help.

    msw

  2. #2
    Lawrence K. Nordell

    Lawrence K. Nordell

    President and CEO

    Conveyor Dynamics Inc. [eDir]

    Conveyor Dynamics Inc.

    Professional Experience 58 Years / 8 Month Lawrence K. Nordell has 58 Years and 8 Month professional experience

    Discussions 2608 Lawrence K. Nordell acceded to 2608 discussions, Articles 0 Lawrence K. Nordell wrote 0 articles, Publications 0 Lawrence K. Nordell Nordell released 0 publications

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    Somewhat depends on how you chose to use the motor and how accurate you calculate the motor demand power.

    1. No dynamic braking: set reserve motor size that surges will not exceed. Usually, the nameplate should be about >20 % over demand or say 75 kW. However, how was the -60 kW derived. Could be the treatment was flawed. Fabric belt (kW) guesses are usually low and consume more power (ie less regenerative) than say CEMA unless the 2/3 kY rule is used zero idler seal drag. Steel cord belt can be more regenerative (ie. lower rolling resistance) due to the power influenced by the bottom/pulley cover thickness. What happens when the belt wears? This will increase the regen. demand.

    2. With dynamic braking - may use more torque with demand regenerative capacity beyond steady-state operation such as with an inverter. Here you can pull back the frequency and if the VFD is designed for 4 quadrant operation the dynamic stopping action will pump the excess energy back to the grid or regen resistor bank. Here the motor size depends on how fast you want to stop. The motor selection depending on the design of the motor torque signature curve and number of loaded stops. A good bet is still in the range of 15-20% over full regenerative demand. This could be higher with faster stopping time.

    I am sure others will offer sage advice beyond these points that relate to their experiences. I often must examine calculation methods of others in an audit role. I urge you to set up a design criteria that you and others follow. Leave room for others to comment on the efficacy of your procedure and recommend an alternative based on their experiences. There are too many items to suggest them all in this response.

    Wishing you success,

    Lawrence Nordell
    Conveyor Dynamics, Inc.
    www.conveyor-dynamics.com

  3. It is difficult to describe here in this forum, the drive selection procedure in detail. However, salient points are as below :
    1) You have to decide conveyor power for varied operation situations, such as empty, 25% load, 50% load, 75% load, 100% load, etc and again all these for varied values of conveying friction coefficient, part length loading etc.
    2) For decline conveyor of negative power, again the conveyor will have positive power when being empty or partially loaded. Therefore, conveyor drive will be operating in positive to negative mode.
    3) Drive motor type can be 3-phase slip ring or squirrel cage motor. If you have maximum negative power of 60 kW at drive motor, you can use 60kW motor. This motor will be operating below synchronous speed during positive power mode, and above synchronous speed when during negative power mode.

    Thus, the motor at any time will be operating say 97% to 103% of synchronous speed (excluding starting and stopping). The motor exact speed in above range will depend upon the magnitude of mtph. The motor operation above synchronous speed has negative torque (restraining torque) which creates balanced speed operation.
    4) The motor and its power supply system should be suitable for regenerative mode operation.
    5) The issue has been taken care in my book on belt conveyor. It includes numerical examples of practical application and calculations for varied operational conditions.

    Trust this provides the basic answer to your query.

    Regards,
    Ishwar G Mulani.
    Author of Book : Engineering Science and Application Design for Belt Conveyor.
    Email : parimul@pn2.vsnl.net.in
    Tel.: 0091 (0)20 5882916

  4. #4
    Lawrence K. Nordell

    Lawrence K. Nordell

    President and CEO

    Conveyor Dynamics Inc. [eDir]

    Conveyor Dynamics Inc.

    Professional Experience 58 Years / 8 Month Lawrence K. Nordell has 58 Years and 8 Month professional experience

    Discussions 2608 Lawrence K. Nordell acceded to 2608 discussions, Articles 0 Lawrence K. Nordell wrote 0 articles, Publications 0 Lawrence K. Nordell Nordell released 0 publications

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    Know-How Design (1521) Lawrence K. Nordell used this tag 1521 times, Pipe Conveyor (238) Lawrence K. Nordell used this tag 238 times, Chutes (119) Lawrence K. Nordell used this tag 119 times

    Contrary to Mr. Mulani:

    I disagree with your advice to size downhill conveyors on the calculated kW. I have never heard of such a practice as to select the drive on the demand or calculated rating. How do you propose to set the governing values to be weighed in this analysis. Arguing that the motor shaft power is significantly influenced by the gear losses is pretty subtle and not very relevant as well as the super-synchronous speed albeit you get more cooling.

    Downhill analysis has many contrary methods of analysis: CEMA, DIN 22101, ISO, AS, JIS, Goodyear, Contitech, and many others.

    In the calculation procedures, stock must be taken of new and of worn or future state of the equipment. Standards differ as does the equivalent friction factor such as:

    CEMA says to eliminate the seal drag in idlers, pulleys skirts and cleaners, and to reduce the belt induced drag by 1/3. Often this can result in a overall drag factor of DIN f < 0.012. DIN 22101 does discuss a similar value down to f = 0.012. Taking these conditions as they apply to small belts is conservative (ie f>0.012) and larger belts the values can drop below f = 0.0085.

    Temperature also can have a dramatic influence.

    In summary, you argue the point of a few percentage points, where as the real world calculation methods vary by tens of percentages, and the real world can vary by much, more depending on the specifics of the conveyor design and products used. You will not find all the answers in a book.

    I suggest MSW take a more cautious approach.

    LKN
    Conveyor Dynamics, Inc.

  5. Hello msw,

    Further to my earlier message, I add following clarification although the same already implies in my message .

    One needs to find out the maximum positive power and maximum negative power among varied operational conditions (parameters), as listed in my message.

    The motor alongwith the electrical system should be capable to suit max positive power and also max negative power demand, as may occur during conveyor operation. Accordingly, motor size will correspond to | kW at motor |. (the symbol || means modulus).
    I have presumed that your mentioned 60 kW is maximum modulus | kW |

    The varied value of conveying friction coefficient also implies likely variation in magnitude of various frictional resistances.

    The aforesaid motor kW may need marginal revision / increase, in accordance with the specific electrical system being considered for stopping. All the varied intricate situation cannot be taken care in such reply, without actual example, while deciding the optimum solution.

    Regards,
    Ishwar G Mulani.
    Author of Book : Engineering Science and Application Design for Belt Conveyor.
    Email : parimul@pn2.vsnl.net.in
    Tel.: 0091 (0)20 5882916

  6. #6
    Join Date
    Jul 03
    Posts
    2

    thanks

    Dear Mr. Nordell and Mr. Mulani,

    Thanks a lot for your helpful replies.

    I got the -60kw of pulley shaft KW with the ISO standard and the overall drag factor f I used is 0.012. The -60kw is the the result of
    full load situation and the maximum posive power is 26kw in
    empty load situation with the overall drag factor f 0.03.

    How should I select the motor power then?

    Best Regards,

    msw

  7. #7
    Lawrence K. Nordell

    Lawrence K. Nordell

    President and CEO

    Conveyor Dynamics Inc. [eDir]

    Conveyor Dynamics Inc.

    Professional Experience 58 Years / 8 Month Lawrence K. Nordell has 58 Years and 8 Month professional experience

    Discussions 2608 Lawrence K. Nordell acceded to 2608 discussions, Articles 0 Lawrence K. Nordell wrote 0 articles, Publications 0 Lawrence K. Nordell Nordell released 0 publications

    Searching nothing specified

    Know-How Design (1521) Lawrence K. Nordell used this tag 1521 times, Pipe Conveyor (238) Lawrence K. Nordell used this tag 238 times, Chutes (119) Lawrence K. Nordell used this tag 119 times

    If I understand you correctly, using the ISO power calculation procedures and you use:

    1. f= 0.012 for the downhill analysis and obtain power = -60 kW

    2. f=0.030 for empty belt and obtain power = 26 kW

    Belt is only downhill with no near flat or incline sections.

    Then I advise to select a 75 kW drive for the reasons previously stated. It is not adviseable to select the motor size at the demand leaving nothing in reserve to cover unknown design or oerating conditions.

    Lawrence Nordell

  8. Down hill motor selection

    MSW,
    I do not know the profile. If it is only down hill, then to get better REGENERATIVE BRAKING normally one size higher motor is selected ignoring the positive power in addition to other type of electrical braking.I did conveyor system in BAILADILA MINES in INDIA considering the same.All conveyor are running well with out over speeding.So you can take 75KW motor as already stated by MR.Nordell.
    Regards.
    A.Banerjee

  9. #9

    downhill conveyor design

    HI MSW
    Mr nordell have given valuable sugessions. Down hill conveyor design is really a challage .
    it is better in case you go for dynamic symulation of this conveyor by reputed consultants who have done the same in past.
    As explained earlier you pl consider every aspect of loading, smooth starting and smooth stopping.
    you also consider mechnism of stopping conveyor in case of power failure.
    Drive should be suitable for delevering retarding torque below syncronous speed under all loading / oprating conditions.
    Type of drive is also very important best but expensive option is 4 quardant control vfd drive .
    you also ensure tension in the system should be high limiting to belt allowable tension,
    A R SINGH

  10. #10
    khalid Guest

    Down hill conveyor Power

    Hi Belt conveyor Designers

    Why you people make simple issue so much complicated.
    It is very difficult to reduce Frictional forces in conveyor however it is easy to induce frictional forces as you like
    In down hill conveyor you just increase friction as well as other powers as defind below to make operating power positive instead of negative
    following additiona forces should be appliedto down hill conveyor
    1.0 Make sure idler bearing and seal friction factor is increased. this can be achieved by providing bush bearings instead of ball bearings
    2.0 provide rollers of 50-60 mm dia so that friction between idler and belt due to identation is increased
    3.0 provide fixed trippers at different locations to give positive lift at some points.
    4.0 provide worm gear boxes to increase drive efficiency
    5.0 provide long skirt plates and thick belt c;eaner to increase resistance
    6.0 pulley bearings can be bushes
    There can be other ways also to increase resistance of downhill conveyor and maske the conveyor power positive from negative

    khalid

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