Removing N-current at HV?

[walker1]

My brother has asked me a strange question.

Apparently the distribution lines (100 kV or more) are Y-coupled. But the neutral current is said to be nearly zero (1-2A), virtually no matter how unballanced the load on the 3-phase consumer net is. (400V European Y with high N-current)

Can anybody give an explanation how this is done?

A Swedish contact of his has mentioned something I translate into a "Mixed Coupling", that takes care of it, but I have found nothing further about it.

I have just found the zigzag transformer, that may do it , but is that it?

 

[rbulsara]

Perhaps your brother can word the question that makes some sense. Have him join the forum and pose his question in his own words and a oneline.

Have him study transformer connections and grounding.

Rafiq Bulsara

http://www.srengineersct.com

 

[ScottyUK]

Each time power passes through a Dy transformer the neutral current on the wye side turns up as a phase imbalance on the delta side. When a large number of consumers are on the system there is an averaging effect on the imbalance, and the rotating machines which form the majority of the load draw symmetrical balanced currents (assuming the voltages are balanced) so at a transmission system level the imbalance is usually swamped in magnitude by the much larger motor loads. Of course there are instances where a large industrial load like an arc furnace, rectifier or a cycloconverter can give rise to neutral currents on the transmission system - often at triplen harmonic frequencies - but these consumers are normally required to have filters and traps to keep the levels below a threshold where they become troublesome to the utility or other users.


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