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STAR/DELTA MOTOR STARTING

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Comments

  • #32
    Randyleprechaun
    Registered Users Posts: 876 ✭✭✭Randyleprechaun


    Does everyone agree(or anyone) that if the overload is on the delta line it should be set at 0.58 X full load amps


  • #33
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Randyleprechaun wrote: »
    Does everyone agree(or anyone) that if the overload is on the delta line it should be set at 0.58 X full load amps

    If its on the delta line or the main contactor it should be set at that value. Only if on the main 3 phases feeding the starter will it be set to full load.


  • #34
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Randyleprechaun wrote: »
    Does everyone agree(or anyone) that if the overload is on the delta line it should be set at 0.58 X full load amps

    If its turning something that is not a heavy load it would usually be put on the main contactor. They are put on the delta contactor to assist with starting up heavy loads to get up to speed because by being on the delta line it is not in circuit until it changes to delta, which means theres a motor running with no overload, so where is the harm in testing with overload bypassed for a few minutes even if it is in delta.


  • #35
    scubaH
    Closed Accounts Posts: 4 ✭scubaH


    If the timer on the star/delta is tampered or changed it will trip out,there should be at least 10 sec interval between the change from star in2 delta,overload should be set at FLC.


  • #36
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    scubaH wrote: »
    If the timer on the star/delta is tampered or changed it will trip out,there should be at least 10 sec interval between the change from star in2 delta,overload should be set at FLC.

    If the motor now has 6 wires feeding it, one set through the main contactor and one set through the delta contactor, and the motor is taking 32 amps per phase, how much will flow down each contactor set, it would`t be FLC i would`t think. And the overloads are usually fitted on one contactor., usually the main one.


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  • #37
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    robbie7730 wrote: »
    If its turning something that is not a heavy load it would usually be put on the main contactor. They are put on the delta contactor to assist with starting up heavy loads to get up to speed because by being on the delta line it is not in circuit until it changes to delta, which means theres a motor running with no overload, so where is the harm in testing with overload bypassed for a few minutes even if it is in delta.

    the 'motor line' overload at 0.58 FLA gives closest protection for 'star' if it doesn't trip on startup

    http://www.patchn.com/index.php?option=com_content&task=view&id=42&Itemid=74


    i imagine a saw should be well below FLA under no-load conditons


  • #38
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    M cebee wrote: »
    the 'motor line' overload at 0.58 FLA gives closest protection for 'star' if it doesn't trip on startup

    http://www.patchn.com/index.php?option=com_content&task=view&id=42&Itemid=74


    i imagine a saw should be well below FLA under no-load conditons

    It does, but they are fitted in the delta leg on heavy slow to speed up setups, and is on the delta leg in this post i think, although i have`t fitted them there myself. The star current will be higher than the delta one ever reaches on any given load possibly. A motor starting takes a current of a seized stopped motor at the instant of starting and in star this is probably higher than it ever takes in the up to speed delta changed over motor.

    And i`d agree, it must be a fair bit below FLA on a saw, so tripping so quick on changeover is interesting.


  • #39
    scubaH
    Closed Accounts Posts: 4 ✭scubaH


    Is the motor going in the right direction?Is it on a C rated MCB back at the board?there should be 1 overload on the outgoing.the current is split.


  • #40
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    As for the overload itself, its not there to protect against short circuits, or insulation breakdown in windings, its there to very closely guard against even a small increase in motor current in motors that are running regular long term. So bypassing it is not a problem for a test purpose in my opinion. And a few grip ammeter tests would take no time and tell a lot about this or any motor setup. A motor thats not seized completely cant suffer any major problems from a bypassed overload as long as its not left bypassed as a fix.


  • #41
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    scubaH wrote: »
    Is the motor going in the right direction?Is it on a C rated MCB back at the board?there should be 1 overload on the outgoing.the current is split.

    How would the MCB at the board have any effect. Maybe the wine is affecting me worse than i thought.


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  • #42
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    robbie7730 wrote: »
    As for the overload itself, its not there to protect against short circuits, or insulation breakdown in windings, its there to very closely guard against even a small increase in motor current in motors that are running regular long term. So bypassing it is not a problem for a test purpose in my opinion. And a few grip ammeter tests would take no time and tell a lot about this or any motor setup. A motor thats not seized completely cant suffer any major problems from a bypassed overload as long as its not left bypassed as a fix.
    ah you might be right:D


  • #43
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    M cebee wrote: »
    ah you might be right:D

    I know, but as you know yourself, i could be wrong as well, theres always something we might not think of.


  • #44
    Randyleprechaun
    Registered Users Posts: 876 ✭✭✭Randyleprechaun


    Thanks again for all the replies guys...case is now closed. I went today to check the control circuit and the motor etc etc. Control circuit was fine but on opening the cover of the motor terminal box I noticed a loose wire which actually broke when I touched it. Must be the vibration or something.

    It was one of the wires leading from the delta contactor so in effect I suppose it was like a phase down.

    Nyway, put it all backj together and it's fine now.

    To clear up some of the confusion(which there seems to be alot of) there are a number of places that the thermal overload can be placed but it affects what the o/l should be set at.
    1. It can go in the motor line but must be set to 0.58 X FLA.
    2. It can go in the delta circuit but must be set to 0.58X FLA
    3. It can go in the main supply(ie. line feeding from MCB or simillar) but must be set to FLA.
    Well thanks again for all the help(even those who went of on their little tangents(argumnents ahem!!!!!))) Sure it's all aprt of the crack ha????


  • #45
    Randyleprechaun
    Registered Users Posts: 876 ✭✭✭Randyleprechaun


    Randyleprechaun wrote: »
    Thanks again for all the replies guys...case is now closed. I went today to check the control circuit and the motor etc etc. Control circuit was fine but on opening the cover of the motor terminal box I noticed a loose wire which actually broke when I touched it. Must be the vibration or something.

    It was one of the wires leading from the delta contactor so in effect I suppose it was like a phase down.

    Nyway, put it all backj together and it's fine now.

    To clear up some of the confusion(which there seems to be alot of) there are a number of places that the thermal overload can be placed but it affects what the o/l should be set at.
    1. It can go in the motor line but must be set to 0.58 X FLA.
    2. It can go in the delta circuit but must be set to 0.58X FLA
    3. It can go in the main supply(ie. line feeding from MCB or simillar) but must be set to FLA.
    Well thanks again for all the help(even those who went of on their little tangents(argumnents ahem!!!!!))) Sure it's all aprt of the crack ha????


    Just to add to the above:

    The 3 different positions for the overload also offer differing levels of protection to the motor


  • #46
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Randyleprechaun wrote: »
    Thanks again for all the replies guys...case is now closed. I went today to check the control circuit and the motor etc etc. Control circuit was fine but on opening the cover of the motor terminal box I noticed a loose wire which actually broke when I touched it. Must be the vibration or something.

    It was one of the wires leading from the delta contactor so in effect I suppose it was like a phase down.

    Nyway, put it all backj together and it's fine now.

    To clear up some of the confusion(which there seems to be alot of) there are a number of places that the thermal overload can be placed but it affects what the o/l should be set at.
    1. It can go in the motor line but must be set to 0.58 X FLA.
    2. It can go in the delta circuit but must be set to 0.58X FLA
    3. It can go in the main supply(ie. line feeding from MCB or simillar) but must be set to FLA.
    Well thanks again for all the help(even those who went of on their little tangents(argumnents ahem!!!!!))) Sure it's all aprt of the crack ha????

    Thats good, its as good as a phase down alright. Its surprising it started in star at all, as even though the 3 phases are there from main contactor, one leg of star point is open, although 2 windings do have 2 phases so it might start. It must of been slow to start though. Although in this case you do have 2 windings still being fed in delta where as a direct on line setup missing a phase would only have one winding being fed properly in delta and the other 2 fed in series from that same 2 phases so all 3 windings would only have single phase,, haha another point for arguements and tangents.


  • #47
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Randyleprechaun wrote: »
    Just to add to the above:

    The 3 different positions for the overload also offer differing levels of protection to the motor

    Yes it does, its simply this, Main feed position its set at FLA, but in main contactor it is set just over half FLA and gives closer protection to starting in star if startups dont have heavy load, and in the delta contactor its also set just over half but gives no protection in star to assist in long slow startup to speed. So putting in main feed at FLA gives protection in star also but gives more room for heavier slow starts than if put in the main contactor set at 0.58

    I must have too much free time on my hands with all the posts :)


  • #48
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    grand job:D

    shows the benefit of the closest 'startup' overload protection if possible(0.58 FLA motor line)


  • #49
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    M cebee wrote: »
    grand job:D

    shows the benefit of the closest 'startup' overload protection if possible(0.58 FLA motor line)

    This motor did`t have the closest `startup` benefit did it?
    The overload was in the delta contactor. So it was`t in the circuit during startup. If one connection in the motor terminal box was gone, then it would not have been starting properly in star either and should of tripped overload during starting if it had been in main contactor set at .58. When it changed to delta it had the double problem of possibly not running up to speed in star as only 2 windings were connected in series to 2 phases, in effect only having single phase startup, and then when it changed to delta it had only 2 windings connected fully. In this scenario its not quite the same as a supply phase down in the delta stage, as 2 of the windings actually have the 3 phases connected, but one winding is open at the motor box connection thats gone bad.

    The closer protection benefit of using the overload at .58 for starting only comes about when its fitted in the main contactor. I think it was in the delta one in this setup. But again i could be missing something.


  • #50
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    that was my point

    it would have been better 'in-circuit' for startup if possible


  • #51
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    M cebee wrote: »
    that was my point

    it would have been better 'in-circuit' for startup if possible

    i know, i`l have to go to specsavers one of these days.


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