Balancing Loads on a three Phase System

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I have a research assignment:
A 3 phase motor and a (3) single phase motor are connected. Can (2) two additional single phase motors be added and keep the Load balanced? It is assumed it is possible. Tell how?
I have a simple diagram as an attachment to make it simple.
 

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GoldDigger

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Judging from the connections, D is the neutral of a three phase four wire wye.

mnkworkstation: Do you think that the person who posed the question is thinking about allowing you to use transformers? (As many and of whatever type as are needed?)
 
My instructor also added that, the system could be any voltage, HP as well as amperage etc. He only wants the two single phase motors (regardless of HP and connection type: Phase neutral or phase phase) be added to keep the load balance.
 

infinity

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My instructor also added that, the system could be any voltage, HP as well as amperage etc. He only wants the two single phase motors (regardless of HP and connection type: Phase neutral or phase phase) be added to keep the load balance.

Sounds like a trick question to me.
 

kwired

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Cool, did not know that. I've never hooked up a noodle to a 3 phase motor.
And you probably shouldn't. Assuming perfectly balanced impedance of each coil, a connected neutral should't carry any current, but throw any point off a little or supply with unbalanced voltage and you can really throw the balance in the motor off if there is a neutral brought back to the source.
 

kwired

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My instructor also added that, the system could be any voltage, HP as well as amperage etc. He only wants the two single phase motors (regardless of HP and connection type: Phase neutral or phase phase) be added to keep the load balance.
Well the actual draw of those single phase motors will make a difference in how balanced everything turns out in the end. If one motor is fully loaded 5 hp it will draw high current on the two lines it is connected to, but if the other two were only 1/2 HP and lightly loaded on top of that - the end balance will not be all that close compared to if all were close to same amount of draw.
 

Smart $

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My professor/Instructor drew this on the board for us to make the research. I guess transformers may be welcome but he didn't make mention of it.
No need for transformers, just connect the two motors either line-to-line or line-to neutral but not the same line-to-line or line-to neutral. Balancing depends on the 1Ø motors having different HP ratings and thus FLA's. Then there's the issue of power factor and whether it plays any role in balancing.

For an overly simplified answer, assign HP of 5, 10, and 15 to the connected 1Ø motors, connect the other two LN to the same lines as the already-connected 5 and 10 conversely to the existing 5 and 10. Single phase motors will have 15 HP connected to each line. The 3Ø motor is irrelevant to the proposal.
 
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