two phases to a 3 ph motor?

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Old 04-05-06, 11:45 AM
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two phases to a 3 ph motor?

So, i'm jogging down one of the streets close by, and I pass one of about 4 lift stations (lucky me). Anyway, we have overhead utility, and all the lift stations, except the newest one use 3 transformers to drive the station. The newest lift station uses 2 transformers, and there is no connection to the 3rd primary wire. So, my question is: Is there a technique of driving the pump motors on only 2 legs?
 
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Old 04-05-06, 11:58 AM
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Originally Posted by telecom guy
So, i'm jogging down one of the streets close by, and I pass one of about 4 lift stations (lucky me). Anyway, we have overhead utility, and all the lift stations, except the newest one use 3 transformers to drive the station. The newest lift station uses 2 transformers, and there is no connection to the 3rd primary wire. So, my question is: Is there a technique of driving the pump motors on only 2 legs?
They are using a transformer connection known as open delta to supply the three-phase power. It only requires two transformers but the supply is limited to less than the full transformer rating.
 
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Old 04-05-06, 01:01 PM
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Old 04-05-06, 06:00 PM
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thanks for those tutorials. I now know a bit about open delta. I remain confused, since my lift station does not tap into the 3rd phase primary at all.
 
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Old 04-05-06, 06:54 PM
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The system may have an open wye primary, where the two primary coils are tapped between primary phases and neutral.

-Jon
 
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Old 04-05-06, 10:27 PM
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It connect to three wires two hots and neutral.

The neutral connection might not be visible from the sidewalk, but it's possible (and usual) to run three-phase with two ungrounded and one grounded conductor.

In fact, in some places you might see only three wires on the pole.
 
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