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Could somebody explain me the difference between Wye and Delta connections?
A Wye (Y) configuration is when all the loads in an AC system are connected at a single point. Normally, the loads are unbalanced in a Y configuration. A neutral cable is connected at that centre point where the three phases meet. Most of the low voltage distribution lines that you see are Y configuration (Red, Yellow, Blue and Neutral).
The Delta configuration has the 3 phases connected like in a triangle. They don't normally have a neutral cable.
In Delta configuration, the phase voltage is equal to the line voltage whereas in Y configuration, the phase voltage is the line voltage divided by root 3 (sqrt(3) = 1.732).
Consequently, in Wye configuration, the phase current and line current are equal while in Delta configuration phase current is line current divided by 1.732.
I found this article on the web which is really helpful to understand:
Also, in the below image, the one on the left is Wye (looks like Y), the one on the right is Delta.
Just a quick note;
SMA SB Installation Manual (pdf), page 23 lists down the common utility voltage configurations.