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Thread: 2 speed motor 3 phase 380 volt motor

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    2 speed motor 3 phase 380 volt motor

    i am doing a new installation of a 2 speed motor. 5.5kw/7.5kw
    i think both windings are internally connected star,so i it should be 2 contactors for slow and fast.
    my question is ,should you use 2 overload relays as the current is different in each speed?

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    Diamond Member AndyD's Avatar
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    Can you give the exact make and model number of the motor? Is it definately wound with two sets of three windings for the two speeds? I'm not sure how this arrangement would work TBH, the rotatonal speed of a 3-phase motor is determined by the number of poles in the windings and I'm not sure if you can have a motor that's wound for example as 4 pole and 6 pole at the same time. Are you sure it's not just a standard wound motor that has the option to be wired in star or delta depending on the application? Without more info I would risk advising on overload protection.
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    Diamond Member Justloadit's Avatar
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    Hi Andy,

    There is such a thing as a dual speed induction machine. I just can not recall the name for it. By switching the connections to the windings, the stator changes from a 2 pole to a 4 pole machine.
    Not very common, but is available.
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    Diamond Member Justloadit's Avatar
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    OK found it it is called a Dahlander motor
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
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    Diamond Member AndyD's Avatar
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    It's possible in theory so I've no doubt some lunatic somewhere will be making them but I've never seen one. If it was a 2-pole and 4-pole arrangement within a single stator then you could be looking at 16 winding wires on the connection termination block. Rather you than me connecting and commissioning Bergie
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    Diamond Member Justloadit's Avatar
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    Hi Andy,

    The Dahlander motor is a a reality, you can order from your local motor supplier.They may not know what you are talking about, but if they are worth their salt they will.
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    i've encountered them a few times ,but fortunately in this application it would be internally connected star. now to find it in EXD . the cheapest i found so far is about R 45000 ex vat for a 5.5kw.
    we have been waiting patiently all these years to see andy get stumped.

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    Just a suggestion if its a new installation why not use a VSD

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    A VSD would be far cheaper, and just as effective. If the client wishes to have 2 speeds only, and is not keen on a potentiometer, then get 2 potentiometers, which are set for the 2 speeds he requires and use a switch to select the pot for the speed required.
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
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    problem is its on portable pumps in hazardous areas. the vsd would have to go inside an ex box which is sealed,but the vsd needs air for cooling. the vsd cant be installed outside the haz area as the pump is portable.

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