Two Speed Single Winding Motor

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rafael rivera

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Can a two speed single winding motor be control by a wye/delta started to change speeds fast to slow without having to stop the motor first?
IMHO with a wye/delta starter this type of motor can be start slow or fast, slow then fast but not fast to slow and change fast to slow and slow to fast as a regular operation.

I need to stand corrected if I have the wrong opinion.

Regards to all.
 
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Phil Corso

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Rafael... a wye-delta starter, even if reconnectible, can't provide the connections to change the motor's speed. The reason is that a W-D motor's winding-ends are acccessible for switching! While the single-winding 2-speed motor's windings are permanently connected in delta. In addition each winding has a center-tap which is swithched to change speed!

Regards, Phil
 
don_resqcapt19

don_resqcapt19

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Why can't you use a re-wired wye/delta starter to control a 3 phase, two speed single winding motor? Low speed would have power to T1, T2, & T3 with T4, T5 & T6 open. High speed would have power to T4, T5 & T6, with T1, T2 & T3 connected together. I can do that with the contactors that are in a wye/delta starter.

That being said, I think the original question was about swithing a motor that is running from fast to slow or slow to fast without first having it come to a stop. I don't know the answer to that.
 
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Phil Corso

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Don... A wye-delta starter, typically, has 6 contacts, 3 each for Start & Run (although, some have 2 for Start and 3 for Run) a typical single-winding, 2-speed starter has 3-contacts for High-speed, and 5 for Low-speed!

Regards, Phil Corso
 
don_resqcapt19

don_resqcapt19

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Phil,
This is the wye delta starter I was thinking about and it looks like it would work with a two speed single winding six lead motor. It looks like if I would reverse the T1, T2, T3 leads with the T4, T5, T6 leads shown on the drawing and engerize 2M the motor would run in low speed. If I energize 1M and S the motor would run in high speed.
 
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Phil Corso

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Don... the schematic presented has enough load-contacts and interlock-contacts to "control" a 2-speed motor.

Also, replying to the "Stop Before Executing a Speed Change" topic, I'm of the very old school that says "make sure the transition from one-speed to the other is delayed enough so that any residual-voltage will have decayed to a safe level."

Regards, Phil
 
don_resqcapt19

don_resqcapt19

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Phil Corso said:
Don... the schematic presented has enough load-contacts and interlock-contacts to "control" a 2-speed motor. ...
Click to expand...
Phil,
I assume that means there are other types of wye delta starters that would not be suitable for the two speed motor. As far as I remember, the design in the link I posted, is the only type that I have worked on, but then I haven't worked a very many wye delta starters.
 
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rafael rivera

Member
Thank you all for your prompt responses.

The motor in question is actually a two speed single winding motor like I mention on the original thread.
I have a design that has a wye/delta starter with three contactors ( Slow, Fast, Shorting Contactors ) to control it with two sets of electronic overload relays one for slow speed the other for fast speed. The application for this motor is for a cooling tower fan and it will be control by DCS outputs signals but also the control wiring has a time delay relay with a N/O contact closing on dropout to latch the Fast Contactor and the Shorting Contactor. ( This is a variable torque motor actually run slow on delta, run fast on wye ) That's telling me we will not be able to switched from fast to slow without stopping the motor first. So my arguiment with the designer is why not a VFD in the first place.
The reason for my arguiment is the same as some of you has already mention while switching from fast to slow with an open transition starter like the aforemention we will have residual voltages issues that will create a whole new set of problem to deal with in the long run.

Your experts opinions are greatly appreciated.
 
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a.bisnath

Senior Member
VFD is the best bet

VFD is the best bet

In the old days where the open transition was to be avoided wound rotor with liquid or solid resistor banks,or the cascaded induction motor would be used,but nowadays with the optimising of efficiency in all areas and also with the prices of VFD's becoming more and more competitive ,the VFD is the way to go
 
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