vector groups

If you are talking about a single transformer they probably are not, but networks usally have multiple transformers on them, and the transformers will only operate in parallel if they produce voltages on the secondary side that are in phase. The vector group must be chosen to achieve this objective.

In a highly standardised supply network all the transformers used for the same purpose will probably be of the same vector group. In the UK pracktically all the 11 kV to LV transformers will be 41 DY 11.

But the 11 kv network may be supplied directly from the 132 kv Network, or there may be an intermediate 33 kv Network. The 132 kV to 11 kV and the 33 kV to 11 kv transformers will be different vector groups in order to keep the 11 kV in phase.

Hope this helps

John

Will someone please explain what a vector group is. To me, "vector" and "group" are mathematical concepts. Ordinary vectors in 3 D form a group under the operation of vector addition.

Bill

-- Fermez le Bush--about two years to go.

In a single phase transformer with a primary and a secondary, and one end of each winding at or about ground voltage, the output voltage will either be almost exactly in phase with the input voltage, or in phase oposition to it (ie 180 degrees apart.

When you go to a three phase transformer, or a bank of three single phase transformers, you have some choices as to how you connect them up. Certainly in the UK "vector group" is how you tell the transformer manufacturer how you want the windings connected, and how the terminals will be labelled. The details are in the transformer standard.

In the example I used in my previous email "41 DY 11" implies that the primary will be connected in delta, and the secondary will be connected in star, and the connections and labelling will be such that the output phase voltage lags the input phase voltage by 30 degrees . The "11" represents 11 o clock on a clock face.

Does that help

John

Thanks.

This just emphasizes that Brits and Americans are separated by the same language. Power engineering is definitely not my forte. If I were doing something along those lines, I would label the phases ABC or even more phases when rectifier connections are to be considered. I would label the ends with dots to indicate corresponding emf. The whole business would become more complicated with zig-zag and other connections to increase the number of phases.

Bill

-- Fermez le Bush--about two years to go.

-------------- It's a matter of convention used for connections. You are applying an approach understood (?) by engineers and useful in analysis of a system while the vector group is another way to put this information in a generally useful way without the need for a great deal of thought by the user (eliminating some errors). The 11 is apparently the phase shift of the corresponding phase (A secondary lags A primary by 30 degrees.) The equivalent can be shown on a diagram in the way that you indicate but in the case of a black box with 6 terminals ABC,abc the vector group designation is convenient.