Determine if the motor is WYE or DELTA

[Askarel27]

The motor that has no nameplate and has only 3 wires out.
How could we know the connection of a motor if it is star or delta?

 

[davidbeach]

Does it matter?

 

[Skogsgurra]

No, it doesn't. Davidbeach is absolutely right.

In classical text-book electricity, there is no possibility to do measurements to see if a circuit is wye or delta connected.

In an induction motor, however, there is a possibility to see the difference: Record the stator voltage when the rotor is rotated and see if you have very low triplen harmonics (use FFT to see frequency contents). Triplens are very low if delta connected since 3x120=360, so they "compensate" each other.

Your problem is that you cannot reconnect and measure wye and delta. So, it doesn't work for you.

But it doesn't matter. So just relax and leave it.



Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[waross]

Disassemble the motor and apply low voltage DC to a pair of leads. Check the magnetic field strength around the inside of the stator with something like a hacksaw blade. You may wish to vary the applied DC voltage until best results are obtained.
Delta: One winding group will be magnetized strongly and the other two groups will be at half strength.
Wye: Two winding groups will be strongly magnetized and one group will be either not magnetized or weakly magnetized.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

Never thought of that! Elegant.
When does one need to know?
(Except for evident cases and when all six wires are available)

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[davidbeach]

If you disassemble the motor, can't you just inspect the connections?

 

[waross]

That may work David. However the connections are not always easy to figure out. On a six lead motor, two winding leads into one supply lead says delta. Two wires connected to one of the three supply leads does not always mean delta. It may be two parallel groups of coils.
Gunnar said it best.
"When does one need to know?"
And to be fair, I seem to remember you saying something similar a few years back, David.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

With only three leads, it has only one voltage rating. Looking in from the terminals, with the three phases connected, there's no was of telling whether it's a delta or an ungrounded wye; taking the motor apart is just cheating. ;-) Nothing in the application of the motor will differ between the two. So, the determination of which it is is entirely esoteric. But, I do like your magnetization test, rather clever that.

Once there's at least 6 leads the whole ball game changes. Nine leads seems to point to one internal wye. Six or twelve leads can be either, or something else altogether. With 6, 9, or 12 it's important to connect it correctly for the applied voltage. But 3 makes it so simple, either it works at the supply voltage or not. No worries about a whole variety of specialized motors that may show up with more than 3 leads.

The OP must have life far too easy and wants to find ways of complicating it.

 

[waross]

And some NEMA motors are 9 lead delta. The higher voltage connections are the same for wye or delta but the low voltage connections are different.
Low voltage wye:- one group of three leads and three groups of two leads.
Low voltage delta:- three groups of three leads.
And some 6 lead motors are single voltage, part winding start.
And then there is 10 lead machines. Used for wye connected generators with what would be the buried wye connection in a motor brought out for the neutral.
10 lead generators are a challenge to reconnect for single phase. Niether the zig-zag connection nor the double delta connection works.
For the lower voltage connection, the Bar-Diamond or Collin connection will work for the lower voltage single phase.
The common voltage of a reconnected genset is 120/240, so the Collin connection works fine.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[zlatkodo]

Nothing in the application of the motor will differ between the two. So, the determination of which it is is entirely esoteric.

For example, in case of single phase use of three phase motor, the capacitor value (consequently HP) depends significantly on whether the connection is delta or wye.

 

[waross]

zlatkodo; Is one or the other preferred for single phase conversions?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[zlatkodo]

Regarding the 3 leads motors, "delta" is preferred if the voltage for single phase use = line to line voltage of three phase motor.