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
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
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).
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.
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.
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:
. 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.
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.