Soft starting a 1,200 HP 4160 volt motor

Discussion in 'Electrical Engineering' started by SimonLW, Jun 20, 2005.

  1. SimonLW

    SimonLW Guest

    We have a very limited power from the utility. We can run the motor, but
    can't start it. This motor turns a very large fan. Is it possible to start
    without exceeding the run current? Since it is just a fan, the run-up time
    can be longer. Thanks!
     
    SimonLW, Jun 20, 2005
    #1
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  2. SimonLW

    SQLit Guest

    "SimonLW" <> wrote in message
    news:...
    > We have a very limited power from the utility. We can run the motor, but
    > can't start it. This motor turns a very large fan. Is it possible to start
    > without exceeding the run current? Since it is just a fan, the run-up time
    > can be longer. Thanks!


    Sure this is done all of the time. Best check with your motor manufacture
    first about this application.
    Then call ABB, I have seen more of their medium voltage stuff than anyother
    manufacture in this kind of application.

    Seems pretty weird that your company would install equipment that they can
    not start. Or is this something your looking to buy?
     
    SQLit, Jun 20, 2005
    #2
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  3. SimonLW

    SimonLW Guest

    "SQLit" <> wrote in message
    news:9HAte.8$...
    >
    > "SimonLW" <> wrote in message
    > news:...
    > > We have a very limited power from the utility. We can run the motor, but
    > > can't start it. This motor turns a very large fan. Is it possible to

    start
    > > without exceeding the run current? Since it is just a fan, the run-up

    time
    > > can be longer. Thanks!

    >
    > Sure this is done all of the time. Best check with your motor manufacture
    > first about this application.
    > Then call ABB, I have seen more of their medium voltage stuff than

    anyother
    > manufacture in this kind of application.
    >
    > Seems pretty weird that your company would install equipment that they can
    > not start. Or is this something your looking to buy?
    >
    >

    Actually it is a client. It is a fan for a flash dryer and they are limited
    by what the utility supplies. They are looking to install this equipment. We
    normally don't deal with this aspect of the design.
    Thanks -S
     
    SimonLW, Jun 20, 2005
    #3
  4. SimonLW

    SQLit Guest

    "SimonLW" <> wrote in message
    news:42b6de38$...
    > "SQLit" <> wrote in message
    > news:9HAte.8$...
    > >
    > > "SimonLW" <> wrote in message
    > > news:...
    > > > We have a very limited power from the utility. We can run the motor,

    but
    > > > can't start it. This motor turns a very large fan. Is it possible to

    > start
    > > > without exceeding the run current? Since it is just a fan, the run-up

    > time
    > > > can be longer. Thanks!

    > >
    > > Sure this is done all of the time. Best check with your motor

    manufacture
    > > first about this application.
    > > Then call ABB, I have seen more of their medium voltage stuff than

    > anyother
    > > manufacture in this kind of application.
    > >
    > > Seems pretty weird that your company would install equipment that they

    can
    > > not start. Or is this something your looking to buy?
    > >
    > >

    > Actually it is a client. It is a fan for a flash dryer and they are

    limited
    > by what the utility supplies. They are looking to install this equipment.

    We
    > normally don't deal with this aspect of the design.
    > Thanks -S


    If they are considering it. Then look into a axial fan and controls. The
    motor starts with the fan blades closed so it is almost a "no load" start on
    the motor. Then as time progresses the controls can open the blades and load
    up the motor. Did this on a 480v 3phase motor for smoke removal. Starting
    amps was an issue with the generator.
     
    SQLit, Jun 20, 2005
    #4
  5. SimonLW

    Brian Guest

    Try using a freq drive. That is if the motor will allow the freq change. Works great for chillers.


    "SimonLW" <> wrote in message news:...
    We have a very limited power from the utility. We can run the motor, but
    can't start it. This motor turns a very large fan. Is it possible to start
    without exceeding the run current? Since it is just a fan, the run-up time
    can be longer. Thanks!
     
    Brian, Jun 21, 2005
    #5
  6. SimonLW

    operator jay Guest

    "Brian" <> wrote in message
    news:O9Jte.49470$oK.30814@okepread02...
    > Try using a freq drive. That is if the motor will allow the freq change.

    Works great for chillers.
    >
    >
    > "SimonLW" <> wrote in message

    news:...
    > We have a very limited power from the utility. We can run the motor, but
    > can't start it. This motor turns a very large fan. Is it possible to start
    > without exceeding the run current? Since it is just a fan, the run-up time
    > can be longer. Thanks!
    >
    >
    >
    >



    A huge frequency drive on a high impedance system could give voltage
    distortion problems. And maybe even liability problems.

    j
     
    operator jay, Jun 21, 2005
    #6
  7. SimonLW

    SimonLW Guest

    "SimonLW" <> wrote in message
    news:...
    > We have a very limited power from the utility. We can run the motor, but
    > can't start it. This motor turns a very large fan. Is it possible to start
    > without exceeding the run current? Since it is just a fan, the run-up time
    > can be longer. Thanks!
    >
    >

    Thanks for all the replies. We looked at VFDs, spinning it up with smaller
    motors and even uglier ideas. We finally told the client to talk to the
    utility. The problem is the supply to the plant is inadequate and the
    utility is complaining about the expense of the miles of wire and equipment
    to deliver the power.
     
    SimonLW, Jun 21, 2005
    #7
  8. SimonLW

    Bob Guest

    On Tue, 21 Jun 2005 07:45:07 -0400, "SimonLW" <> wrote:

    >"SimonLW" <> wrote in message
    >news:...
    >> We have a very limited power from the utility. We can run the motor, but
    >> can't start it. This motor turns a very large fan. Is it possible to start
    >> without exceeding the run current? Since it is just a fan, the run-up time
    >> can be longer. Thanks!
    >>
    >>

    >Thanks for all the replies. We looked at VFDs, spinning it up with smaller
    >motors and even uglier ideas. We finally told the client to talk to the
    >utility. The problem is the supply to the plant is inadequate and the
    >utility is complaining about the expense of the miles of wire and equipment
    >to deliver the power.
    >


    The utility will most likely not be of much help. They tend to tell
    users to either cough up a ton of money to upgrade the feed to their
    new system, or they tell them to limit the starting kVA. Along those
    lines, there are 3 choices.

    1) A VFD, but at 4160V you will be looking at $250,000 by the time it
    is all said and done. The advantage: a VFD can start the load at 100%
    FLA, and since you alrerady know the system can handle 100% FLA, you
    know in advance that the VFD will work.

    2) Pony motor starting. This is the suggestion from above wherein you
    can use a small motor to get the fan moving, then switch over to the
    main motor after it is already spinning. Theoretically it could work,
    but when the 4160V motor is connected, there is still a massive inrush
    even if the fan is already moving, just smaller by a few percent. This
    is very expensive to experiment with only to find out it didn't work!
    They also tend to add mecahnical safety issues to the problem.

    3) Reduced Voltage Starting. This is what was mentioned above as
    either Autotransformer (RVAT) starting or Solid State (RVSS) starting.
    In this HP size the RVAT will be slightly cheaper (if you ignore motor
    protection issues), but riskier and very big and heavy in comparison.
    Risky because again, you are not 100% sure it will work until you try
    it. RVSS is going to cost more up front, however most RVSS starters
    now come with protection systems comparable to Multilin Relays
    built-in, so if you add the cost of that to an RVAT, it comes out
    even. The best part is that RVSS manufacturers will often do a
    Transient Motor Starting analysis for you for free if you can provide
    all the motor, power system and load data to them. I used Motortronics
    on 3 projects last year and every one of them came out dead on to the
    TMS analysis they did prior to my purchasing them. So I knew in
    advance that it would work before I purchased them. On a 4th project,
    the utility restrictions were too severe so I had to use a VFD.
    Motortronics ran the TMS study for me and told me that any RVSS would
    not work, so essentially they lost the order. So at $25,000 each for
    the RVSS's and $250,000 for the VFD, I looked at it as though
    Motortronics saved me $225,000 each on 3 projects! The Motortronics is
    the one sold by ABB as well as mentioned above. The first ones I used
    5 years ago came from ABB as part of a package deal, and I would still
    go that way again if the project called for it, but when I just wanted
    the starters alone, I went directly to the manufacturer.

    If you want to get more opinions on this, try logging onto
    http://eng-tips.com and go to the Electric Motors and Controls forum
    to post a question. Great resource, free as long as you register, and
    they DO NOT sell your email address.
     
    Bob, Jun 29, 2005
    #8
  9. SimonLW

    SQLit Guest

    "Bob" <> wrote in message
    news:...
    > On Tue, 21 Jun 2005 07:45:07 -0400, "SimonLW" <> wrote:
    >
    > >"SimonLW" <> wrote in message
    > >news:...
    > >> We have a very limited power from the utility. We can run the motor,

    but
    > >> can't start it. This motor turns a very large fan. Is it possible to

    start
    > >> without exceeding the run current? Since it is just a fan, the run-up

    time
    > >> can be longer. Thanks!
    > >>
    > >>

    > >Thanks for all the replies. We looked at VFDs, spinning it up with

    smaller
    > >motors and even uglier ideas. We finally told the client to talk to the
    > >utility. The problem is the supply to the plant is inadequate and the
    > >utility is complaining about the expense of the miles of wire and

    equipment
    > >to deliver the power.
    > >

    >
    > The utility will most likely not be of much help. They tend to tell
    > users to either cough up a ton of money to upgrade the feed to their
    > new system, or they tell them to limit the starting kVA. Along those
    > lines, there are 3 choices.
    >
    > 1) A VFD, but at 4160V you will be looking at $250,000 by the time it
    > is all said and done. The advantage: a VFD can start the load at 100%
    > FLA, and since you alrerady know the system can handle 100% FLA, you
    > know in advance that the VFD will work.
    >
    > 2) Pony motor starting. This is the suggestion from above wherein you
    > can use a small motor to get the fan moving, then switch over to the
    > main motor after it is already spinning. Theoretically it could work,
    > but when the 4160V motor is connected, there is still a massive inrush
    > even if the fan is already moving, just smaller by a few percent. This
    > is very expensive to experiment with only to find out it didn't work!
    > They also tend to add mecahnical safety issues to the problem.
    >
    > 3) Reduced Voltage Starting. This is what was mentioned above as
    > either Autotransformer (RVAT) starting or Solid State (RVSS) starting.
    > In this HP size the RVAT will be slightly cheaper (if you ignore motor
    > protection issues), but riskier and very big and heavy in comparison.
    > Risky because again, you are not 100% sure it will work until you try
    > it. RVSS is going to cost more up front, however most RVSS starters
    > now come with protection systems comparable to Multilin Relays
    > built-in, so if you add the cost of that to an RVAT, it comes out
    > even. The best part is that RVSS manufacturers will often do a
    > Transient Motor Starting analysis for you for free if you can provide
    > all the motor, power system and load data to them. I used Motortronics
    > on 3 projects last year and every one of them came out dead on to the
    > TMS analysis they did prior to my purchasing them. So I knew in
    > advance that it would work before I purchased them. On a 4th project,
    > the utility restrictions were too severe so I had to use a VFD.
    > Motortronics ran the TMS study for me and told me that any RVSS would
    > not work, so essentially they lost the order. So at $25,000 each for
    > the RVSS's and $250,000 for the VFD, I looked at it as though
    > Motortronics saved me $225,000 each on 3 projects! The Motortronics is
    > the one sold by ABB as well as mentioned above. The first ones I used
    > 5 years ago came from ABB as part of a package deal, and I would still
    > go that way again if the project called for it, but when I just wanted
    > the starters alone, I went directly to the manufacturer.
    >
    > If you want to get more opinions on this, try logging onto
    > http://eng-tips.com and go to the Electric Motors and Controls forum
    > to post a question. Great resource, free as long as you register, and
    > they DO NOT sell your email address.


    Reduced voltage starters that I have worked on will not limit the current
    much. Starting current values on our 4160 chillers are 3/4 of full load.
    'course that could be the operators. I just look at the load data once a
    month.

    No one ever said that medium voltage was inexpensive.

    One other thing that you should be aware of,
    Unless the technology has gotten a lot better in the last couple of years.
    Medium voltage motor controls really do not like heat. I know of a water
    pumping plant in N. Phoenix that has a 10 ton air conditioner sitting on top
    of their medium voltage VFD's. In the summer time the room runs constantly
    at about 85-90 F. So if your application in in a warm place best check with
    the manufacture before going very far. Eaton/Cutler-Hammer used to produce
    low voltage VFD's and Softstarts that were rated at 40 C. When I called they
    thought I was crazed until I sent the temp information for my desert. We
    ended up ducting a/c directly into the bottom of the vfds to keep them
    running in the summer months.
     
    SQLit, Jun 29, 2005
    #9
  10. SimonLW

    operator jay Guest

    "SQLit" <> wrote in message
    news:c3Cwe.44$...
    >


    >
    > Reduced voltage starters that I have worked on will not limit the current
    > much. Starting current values on our 4160 chillers are 3/4 of full load.
    > 'course that could be the operators. I just look at the load data once a
    > month.
    >


    Across the line starting current is normally given as 600% or so of full
    load current. Often soft starters limit current to 300% of full load
    current, or maybe 150% of full load. Dropping starting current to 75% of
    full load sounds very low. There are instances where this wouldn't even
    produce enough torque to get the motor running.

    j
     
    operator jay, Jun 30, 2005
    #10
  11. SimonLW

    SQLit Guest

    "operator jay" <> wrote in message
    news:KtHwe.6229$...
    >
    > "SQLit" <> wrote in message
    > news:c3Cwe.44$...
    > >

    >
    > >
    > > Reduced voltage starters that I have worked on will not limit the

    current
    > > much. Starting current values on our 4160 chillers are 3/4 of full

    load.
    > > 'course that could be the operators. I just look at the load data once a
    > > month.
    > >

    >
    > Across the line starting current is normally given as 600% or so of full
    > load current. Often soft starters limit current to 300% of full load
    > current, or maybe 150% of full load. Dropping starting current to 75% of
    > full load sounds very low. There are instances where this wouldn't even
    > produce enough torque to get the motor running.
    >
    > j


    I was not speaking of a soft start.
    Reduced voltage stuff we have at 4160 v has an auto-transformer in the
    circuit until the start windings are used.
     
    SQLit, Jun 30, 2005
    #11
  12. SimonLW

    Mike Lamond Guest

    "SQLit" <> wrote in message
    news:8MJwe.581$...
    >
    > "operator jay" <> wrote in message
    > news:KtHwe.6229$...
    >>
    >> "SQLit" <> wrote in message
    >> news:c3Cwe.44$...
    >> >

    >>
    >> >
    >> > Reduced voltage starters that I have worked on will not limit the

    > current
    >> > much. Starting current values on our 4160 chillers are 3/4 of full

    > load.
    >> > 'course that could be the operators. I just look at the load data once
    >> > a
    >> > month.
    >> >

    >>
    >> Across the line starting current is normally given as 600% or so of full
    >> load current. Often soft starters limit current to 300% of full load
    >> current, or maybe 150% of full load. Dropping starting current to 75% of
    >> full load sounds very low. There are instances where this wouldn't even
    >> produce enough torque to get the motor running.
    >>
    >> j

    >
    > I was not speaking of a soft start.
    > Reduced voltage stuff we have at 4160 v has an auto-transformer in the
    > circuit until the start windings are used.
    >

    I learned about the starting torque problem a few years into my career
    while programming PLC controls for centrigual chillers. Fortunately, the
    motor controls weren't my problem. One site, a new central utility plant,
    had two 4500 HP and one 1750 HP chillers with RVAT starters. They
    started one big chiller with no problem and put a load on it. When they
    went to start the second one, the entire building lost power almost
    immediately after the start contactor closed. It turned out someone at the
    engineering firm had underestimated the starting demand, and the brand
    new substation had tripped on overcurrent. When asked about switching
    the autotransformer tap from 65% to 50%, the chiller manufacturer's
    engineers determined that the motor wouldn't have enough torque to
    start turning the motor, speed increaser (1:3.2 gearbox) and compresssor.
    The owner and engineer were forced to put in a larger service.

    Closing the intake dampers on startup will also help. I watched the
    contractors go mad trying to start a 100 HP multistage centrigual
    aeration blower with the intake valve fully open and not trip the solid
    state starter. They were convinced that pulling a vacuum against a
    closed valve took more current than moving air.

    Here's another thought - is it any less expensive to install and operate
    cogeneration at the plant than to pay the utility to install more new
    equipment with more capacity? It's more complex, and depends on
    the availability of fuel, usually natural gas, oil or excess plant steam.
    If a 1200 HP load pushes the existing supply to its limits, where will
    the power come from for any future growth?

    Mike
     
    Mike Lamond, Jun 30, 2005
    #12
  13. SimonLW

    operator jay Guest

    "SQLit" <> wrote in message
    news:8MJwe.581$...
    >
    > "operator jay" <> wrote in message
    > news:KtHwe.6229$...
    > >
    > > "SQLit" <> wrote in message
    > > news:c3Cwe.44$...
    > > >

    > >
    > > >
    > > > Reduced voltage starters that I have worked on will not limit the

    > current
    > > > much. Starting current values on our 4160 chillers are 3/4 of full

    > load.
    > > > 'course that could be the operators. I just look at the load data once

    a
    > > > month.
    > > >

    > >
    > > Across the line starting current is normally given as 600% or so of full
    > > load current. Often soft starters limit current to 300% of full load
    > > current, or maybe 150% of full load. Dropping starting current to 75%

    of
    > > full load sounds very low. There are instances where this wouldn't even
    > > produce enough torque to get the motor running.
    > >
    > > j

    >
    > I was not speaking of a soft start.
    > Reduced voltage stuff we have at 4160 v has an auto-transformer in the
    > circuit until the start windings are used.
    >
    >


    I tend to refer to autotransformer starters as soft start too. I have not
    looked into medium voltage applications but at low voltages, the lowest taps
    I see on Reduced Voltage Auto Transformer starters are 50%, giving 25% of
    across-the-line starting current at the primary -- however across-the-line
    starting current is typically 600% of full load current, so RVAT starting
    current is still 150% of full load current. A starter that dropped starting
    current to 75% of full load current would be great for starting a motor
    without jolting the mechanical load. Or for starting a motor on generator
    power. I am surprised to see a number that low (75%), is all.

    j
     
    operator jay, Jun 30, 2005
    #13
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