# Advantages of three phase systems over single phase

1. ## Advantages of three phase systems over single phase

Hi, Can anybody help me??
Describe the advantages of three phase systems as opposed to single phase and list the different methods of connection. Include the relationship between line and phase voltage and current for each type??
Any help would be greatly appreciated, regards, Tom

2. ## Re: Three phase systems?

School work, yes?

One advantage is that the physical strenght of a three phase cable is greater because it have three or four wires instead of just two.

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3. ## Re: Advantages of three phase systems over single phase

Three phase has higher voltage and can drive high volume of mass if it used for a pulling or rotating job. more power more work can be completed.

4. ## Re: Advantages of three phase systems over single phase

Originally Posted by koppan
Three phase has higher voltage . . .
This isn't always the case

Beside, he's semester is finished and the question is likely solved long time ago.

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5. ## Re: Advantages of three phase systems over single phase

The big advantage with 3 phase mains is that any electric motor connected to it is more efficient, has smother running and uses less parts so is more reliable. There is also a slight advantage in using 3 phase transformers over single phase ones. There is a great advantage in AC to DC power supplies as smaller capacitors can be used. For other applications such as heating and lighting it has no advantage.
Frank

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6. ## Re: Advantages of three phase systems over single phase

The 3 phase system has an advantage for the single phase system for sure, the 3 phase system has more power than the single phase system, such that p=3vicos(theta).

7. ## Re: Advantages of three phase systems over single phase

Three phase motors are inherently self-starting because of the rotating filed produced by the 3 phase current.
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If the load is balanced, there is no neutral current flow (in the case of a Y (Wye, Star) connection.
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In a delta connection, you can lose (open) one phase, and you still have three phase power available, although thecurrent flow from the source will be greater.

8. ## Re: Advantages of three phase systems over single phase

Originally Posted by Kral
In a delta connection, you can lose (open) one phase, and you still have three phase power available, although thecurrent flow from the source will be greater.

9. ## Re: Advantages of three phase systems over single phase

The delta connection in which one phase (Secondary Winding) is missing is called the "open delta" connection. The following article explains it better than I can:
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E.T.E. 3 Phase Transformer Info
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This connection is useful in situations where the load is expected to grow over time. You can start initially with an open delta, and as the load requirements increase, you can add the third transformer without disturbing the system.

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10. ## Re: Advantages of three phase systems over single phase

I guess, the open delta configuration is a typical US special. I noticed, that in the US, it's still common to mount three single phase transformers on a power pole instead of a more economic three-phase transformer. In this case, you can think about omitting one for reduced load. Unfortunately, you get asymmetric current capabilities of each phase.

11. ## Re: Advantages of three phase systems over single phase

I still disagreed with your statement that I quoted.

However, you could just add "by using two single phase transformers" to make the statement true.

An open delta configuration must contain two identical single phase transformers.

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