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Y or Delta configuration?

Discussion in 'Electrical Engineering' started by Hiking, Mar 9, 2005.

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  1. Hiking

    Hiking Guest

    Hello all,

    We have a motor which can be hooked up either in Y configuration, or
    Delta configuration. Which configuration will give more start torque,
    and then the most operational torque, and why in each case?

  2. SQLit

    SQLit Guest

    Looking on the name plate of the motor has not explained the difference?

    Or is this a home work question?
  3. Guest

    I would say delta since it might be slightly more efficient (240 vs
    208v) but the difference would be miniscule. What do you have in the
    building? That is what you will use.
  4. Edd

    Edd Guest

    Is this a wye start delta run single voltage motor or a dual
    voltage motor with a voltage ratio of 3^.5?

    .... Is it ignorance or apathy? I don't know and don't care.
  5. CLT

    CLT Guest

    The 2 configurations will give you the same power, couse the delta
    config is for lower voltage, let say 220 or 110 volt 3 phase and the
    Y config is for higer voltage, 380 or 220 volt 3 phase. The are
    motors that use 660 volt for high (Y) and 380 for low (delta).
  6. Hiking

    Hiking Guest

    Never mind guys, I wasn't so much concerned with which configuration to
    connect for its own sake, the boys here will do trial-and-error and will
    wire it from there. The guys here don't care why. For myself, I was
    only interested in the "why", in understanding the "why"s of this situation.

    I remember from school many, many years ago that torque was a result of
    the phase differential between the outer winding (what do you call this
    one again?) and the induced EMF in the armature, the greater the
    difference, the more torque you get. As the armature gains speed and
    nears synchronization with the rotating EMF in the outer core, the
    torque is reduced conversely. I understand the EMF in the outer core is
    not really "rotating", but the effect is of a rotating field... and if I
    understand this correctly, by increasing the frequency of the outer-core
    field, one could increase the operational speed of the armature,
    correct? I suspect, however, that this higher frequency would also
    result in a reduced starting torque capability for the same motor?

    But this is in a Squirrel Cage, single-phase induction motor, I have no
    idea what the situation is with a 3-phase motor... I expect it's the
    same operational principle, only difference being that there are three
    outer-core windings.

    What I was really hoping to understand is how these dynamics are
    different with these two different wiring configuration.

    If anyone can explain what happens in this motor/system under these two
    varying configurations, and has the time and desire to explain it, I am
    all ears and appreciative.

    Can you guess I drove my elect teacher nuts? I have to hand it to him,
    however, he was extremely knowledgeable about the internal, theoretical
    method of operation of elect motors... good 'ol Mr. O'Brien. Though he
    seemed to think it was a waste of time for me to understand elect theory
    to this level, he did humour me and I did understand a lot of it and it
    still is a big help... the problem being that as soon as I learned it, I
    ended up going into another field of work and never used/applied, nor
    thought of electricity since, for over 12 years, so, unfortunately,
    forgot a lot, and am just trying to refresh my memory.

    If you're in a teaching mood, I'd love to learn/understand this subject
    a whole lot better. Thanks.
  7. Bud

    Bud Guest

    My recollection is that Y start delt run is normally for high HP motors.
    The windings are the same but you connect them differently. You
    start in Y configuration, which draws less current (you don't have full
    line voltage across the windings), then switch to delta to run. Ths
    requires a Y-delta starter or connecting multiple starters to do the
    same. A Y-delta starter probably has the contactors mechanically
    interlocked, which is better.
    Y-delta is to reduce the start current on large HP motors - so you don't
    dim the lights on your block - also may be used for high inertia
    mechanical loads that take a long time to start.
    3 phase squirel cage motors operate the single phase except you don't
    need a start winding because the 'rotation' of the phases gives a
    direction for the rotor to turn.

    Your description sounds good. The current in each phase produces what
    appears to be a rotating magnetic field in the stator. This produces a
    current in the cast aluminum bars in the rotor. The induced current
    produces a magnetic field that pulls the rotor to catch up with the
    stator's rotating magnetic field. The greater the difference between the
    stator field rotation and the rotor rotation, the greater the rotor
    current and thus torque. The rotor can' rotate as fast as the stator's
    magnetic field (synchronous speed) because there is no torque at that
    speed. The difference between the speeds is the "slip". Hope this isn't

  8. Hiking

    Hiking Guest

    Thanks Bud,

    that seems to confirm that I have the right idea about how the motor
    works, or is made to work (rotate), but what I'm trying to visualize is
    the different winding configs (Y as opposed to Delta), and how each
    works (trying to understand this in the same way as I understand the
    1-phase Squirrel Cage induction motor).

    Now 'THAT' may be overkill, but if someone wants to tackle it, I'll take
    the beating.
  9. Don Kelly

    Don Kelly Guest


    The rotating field of a 3 phase motor is a true rotating field. That of a
    single phase motor has two rotationg components acting in opposite
    directions. The 3 phase machine doesn't need special tricks to get started
    and has smoother torque than a single phase machine as well as a better
    size(weight) to power ratio.
    The rotor only sees the rotating field. The torque is dependent on speed as
    you indicate and the output power depends on the product of torque and
    speed. Consider a 3 phase 208V 1 HP 1760 rpm motor. supplied at 208V and
    connected in delta. The torque at rated speed will be the same as that of a
    208V, 1HP 1760rpm motor connected in Y. The line current and voltage will be
    the same in both cases but the coil voltage will be higher by a factor of
    root(3) in the delta than in the Y. The coil current will be lower in the
    delta by the same factor. Total power input will be the same at a given
    torque and speed. A delta winding will have more turns per coil by the same
    factor so the ampere turns producing the field will be the same in both
    machines. The rotor doesn't see the difference. A dual voltage machine is
    designed with multiple coils per phase which can be reconnected to either Y
    or delta without exceeding coil voltage and current ratings.

    There is no rotating stator emf by the way- there is a rotating field which
    induces an emf in a shorted rotor which in turn produces a rotating field in
    synchronism with the stator field but not in phase. (The rotor field moves
    at slip speed with respect to the rotor and the rotor is moving at
    synchronous speed -slip speed with respect to the stator so the rotor field
    is synchronous but lagging behind the stator field).

    I think I have some notes around which are in Microsoft word format and
    possibly in HTML format. Equations might get a bit messed up- will check.

    Don Kelly

    remove the urine to answer
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