How to read sequence diagrams of XFMRs, generators, etc.? - Electrical - Engineer Boards Jump to content
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How to read sequence diagrams of XFMRs, generators, etc.?

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It's not clear to me how to interpret whether current will flow through (or in) a piece of equipment e.g. XFMR) given its sequence diagram.  Specifically, zero sequence is confusing me, because my understanding is that it has to involve ground (is that accurate or a misnomer?).  Refer to the diagrams below.  Generally speaking, are we looking to see whether there's a connection between P and Q?  Between P and ground?  Between Q and ground?  How exactly do you read these?  

For example:

Item #1 -- Grounded Wye-Ungrounded Wye -- There's no connection between P and Q, so this means no zero sequence current will flow through the XFMR?

Item #3 -- Grounded Wye-Delta -- The Camara book says that a Delta secondary will permit zero sequence current, but the diagram below (3rd from top) shows a connection between the Primary winding and ground.  Does this mean that zero sequence only flows on the primary side for a fault on the primary?  That is, if there's a fault on the Delta secondary, no zero sequence current will by supplied from the primary side, therefore no zero sequence current will exist?



If the image below doesn't appear, here's a link  There are similar diagrams in Camara on p36-13.


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The zero sequence current is a ground current by definition.  If the system is ungrounded, there will be no zero sequence current.

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