Tertiary winding

[robertplant]

What is the purpose of a tertiary winding on a transformer?

 

[waross]

Sometimes to have another voltage available, sometimes to provide a path for third harmonic currents in a core form three phase transformer.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Marmite]

Also the presence of the teriary winding redistributes inbalanced currents which minimises the effect upstream.

Regards
Marmite

 

[wolf39]

robertplant

In Germany a tertiary winding is called "Ausgleichswickung". This can be translated to "compensation winding" or "equalizer winding", which very well explains the purpose of such a winding. A tertiary winding is a winding which usually is an internal winding, not transmitting power to the outside. Tertiary windings are always of the delta type, in most cases designed for only 6 kV. The purpose of a tertiary winding is to maintain a perfect Ampere-turn balance on all three core legs of a wye/wye transformer, regardless of the star point load. The majority of the HV grid coupling transformers are of the wye/wye type as a HV delta winding is very expensive because of the extra insulation required (a delta winding has 73% more turns than a wye winding, the copper weight is about the same). Wye/wye transformers with a tertiary winding are permitted to carry a full load star point current. Without a tertiary winding some standards are limiting the star point load current to 10%, or less, in order to avoid excessive voltage unsymmetry.

You may also look into threads 242-114285 and 238-125717 for additional information.

Regards

Wolf

http://www.hydropower-consult.com

 

[davidbeach]

in most cases designed for only 6 kV

Not even close to being true; I've never seen one less than about twice that voltage. They can probably be anything the transformer purchaser wants to specify. Tertiary winding are also often used for station services.

 

[dpc]

Also, three winding transformers are fairly popular in large industrial facilities for serving two medium voltage buses from a single primary. I have also seen 4160 V secondary and 480 V tertiary.

 

[wolf39]

David:

Thanks for your comment.

If the transformer purchaser wants a third (active) winding for station services, he gets it, of course. In such case he can specify any voltage. A third winding used for station services, for instance, has its specific purpose. This is obvious and I believe that Roberts question didn't go this direction. I assumed that he wanted to know what a "hidden", i.e. not power transmitting third (tertiary) winding, is for. This I tried to explain.

The transformer designer tries to keep the voltage of a compensation (tertiary) winding low for economical reasons. Still, you are right by questioning my 6 kV figure, which I herewith withdraw. The design voltage of a compensation (tertiary) winding can be as high as 30 kV, and even higher, depending on the transformer output and voltage. A 6 kV figure may be reasonable for, lets say, a 20 MVA/110 kV transformer.

Regards

Wolf

http://www.hydropower-consult.com

 

[lansford]

We have several 10MVA,33KV/4KV oil filled grounded wye grounded wye formerally used on utility applications now feeding 4 KV motors. They have a delta tertiary winding which is not brough out of the transformer used for stabilization since I expect the core is of three leg design.
JIM