Zigzag X'mer

A "Zig-Zag" Transformer offers a low impedance for the flow of zero-sequence currents and a high impedance for positive and negative sequance currents. Hence, it is very useful in creating an 'artificial neutral' where neutral is not available for earthing.

In a zig-zag or interconnected star transformer, there are two identical windings on each leg. The windings are cross-connected such that each core leg is magnetized by the currents from two phases. All windings have the same number of turns but each pair of windings on a leg is connected so that their magneto-motive forces (MMF) are equal and opposite. The result is that the common (star) point is forced to remain at an equipotential voltage with respect to each phase.

The application of the zig-zag transformer is recommended because the required capacity of the star/ delta transformer is 1.73 times as great as that for the zig-zag transformer for the same performance.

Please don't tell me stories, explain to me using schematic and mathematical calculations.

Thanks for you cooperation.

Well, good people have tried to help, and you have responded like this?

Try this link : zig zag transformer

Are you paying fees that you look so angry and need the schematic. If you dont want to listen the stories, find by yourself.

Sorry,clear schematic with example using mathematical calculation will explain the idea in easy way for understanding - I think you didn't work as a teacher before.

let me also give some information and it may help you.

If a neutral point is required which otherwise is not availabel, a zigzag transformer is used. These transformers do not have secondary winding. Each limb of the transformer has two identical windings wound differetially such that under normal conditions that total flux in each limb is negligibly small and therefore the transformer draws very little magnetising current. The ground transformers ar of short time rating usually 10 second to 1 minute. Therefore the size of such transofmers are small as compared to the power transformers of the same ratings

Here its schematic.

The bank can be sized according to the neutral current and the neutral voltage, multiplying by a factor "K" and this "K" is obtained by the amount of time for the relay to open a breaker.
Suppose, if you have a ground fault 5000 ampere and neutral voltage of 6.35kV, the three phase kVA rating of the zigzag will be

(6.35*5000*K) = Zigzag's kVA

K is determined

Note: if a zigzag transformer is not available, a star delta transformer can be used without loading the delta side.

Hope it will be useful for you.

I can see from the schematic that the Zigzag X'mer consists of three branches and each branch consists of two coils.

My question now :

Are those two coils equal in the number of turns but out of phase ?

yes, each phase has two identical windings, which are wound in opposite directions to give the high impedance to normal phase currents

Also see these links.


www.basler.com/downloads/3phXfmrs.pdf

http://www.postglover.com/Literature/GT210-08_Zigzag_Trans.pdf

Thanks for you reply, could you please explain for me in a simple manner how the Zigzag X'mer works referring to its 6 coils.

Any one knows why it is called "Zigzag" transformer ?