Why in 3-phase distribution transformer, primary is delta connected and secondary is star connected?

As we know that delta has 3 connecting points and star has 4 connecting points, during transmission we do not need a neutral line, and if we use it, it will add unnecessary cost. It also helps us to save copper and results in no distortion of the third harmonic current. So the primary is delta connected. Now in the secondary star connection has 4 connecting points i.e. R,Y,B,N. So during distribution if someone needs single-phase supply then we can take one phase and neutral wire and can give them a single-phase supply.

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