induction motor performance

[redraven6]

Three-phase induction motors are being supplied by an OPEN Y-DELTA transformer bank, i.e., there are only two primary phases.

If one of the primary phases opens, what is the effect on the motors ?

 

[Skogsgurra]

Stops. No voltage available.

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.

 

[LionelHutz]

The middle point of the Y primary must be grounded to use an open Y connection so I'd say you'd get a single phasing condition.

 

[Skogsgurra]

An open Y? Is there such an animal? What does a closed Y look like then?

Or do you mean a V connection?

Gunnar Englund

http://www.gke.org

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

 

[davidbeach]

Open wye is phase-neutral-phase. Used (with open delta secondary) where only two of the three phase conductors are available but 3-phase service is desired.

 

[waross]

Consider a four wire wye primary and a delta secondary. Remove one of the transformers. This is called open delta in North America. I believe that this is called a "V" connection in Europe. What you call an open delta we call a broken delta. Three transformers in delta configuration but with one corner of the delta open.
If you lose one phase the other phase will still provide full voltage and any running motors will be singled phased.

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

 

[Skogsgurra]

Ok, separated by a common language?

Gunnar Englund

http://www.gke.org

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

 

[waross]

On a side note, it is possible to get 120/240 Volts three phase from two primary phases and a neutral. I have read about it once and found one engineer in the field who was familiar with it. He called it a Winipeg connection.
The first transformer on A phase is connected as a single phase distribution transformer which in North America has the secondary center tap/neutral grounded. This gives us A phase from L1 and L2. Two more transformers are connected to B phase. One of these transformers is connected to the neutral point to provide B phase. The third transformer is connected to L3 of the first transformer in such a direction as to produce C phase.
Typical transformer sizes may be 50 KVA, 25 KVA and 25 KVA.

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

 

[ScottyUK]

Bill,

Have a look at a Scott connected transformer. I can't claim to have invented it, but sounds similar to what you describe.


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If we learn from our mistakes I'm getting a great education!

 

[waross]

Not at all Scotty. The connection looks like this.
[tt]
B
/
/
A _____/_____ D
N /
/
/
C[/tt]
A-D is one transformer. (It may be two transformers if there is enough space on the pole to mount four transformers.)
N-B is the second transformer.
D-C is the third transformer.
Voltage drops on the primary neutral may contribute to voltage unbalances.
An open delta (or "V" connection on your side of the pond) is used to develop C phase.
I first learned of this connection on Eng-Tips. I think that I remember that a poster was having some voltage balance issues that were probably related to voltage drop in the primary neutral conductor.


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