3 winding transformers - fluxing

[simonfr]

Looking for some inf9ormation regarding 3 winding transformers and a question i have.

Looking at a design which requires a 3 winding transformer. 66kV on primary, 11kV on Secondary and 415V on tertiary. The 66/11kV winding is 5MVA to power a specific bit of plant, however the 66kV/0.415 tertiary winding is for ancilaries such as auxiliary supplies - in the order of 100kVA.

The tertiary winding needs to be permanently energised to power the auxiliaries and the control system. The main power winding will be as an when required fo the primary/secondary winding will not be energised 100% of the time.

Is there a risk that the 66kV/0.415V tertiary winding shall not operate effectively when the main primary/secondary winding is operational? is a 66/11/0,415kV transformer feasible?

Ive had a look through the forum history and its not that clear.

 

[waross]

We had a customer with a 13.2kV/4.16kV/120:208V transformer.
When the store was built, supply was 4.16kV.
The utility informed the customer that the long range plan was to eventually upgrade the supply to 13.2kV.
The transformer worked as a 4.16kV to 120:208 Volt transformer for about 15 or 20 years.
When the utility was finally upgraded to 13.2kV, the 4.16kV winding was used to power a 4.16kV air conditioner motor.
The main load continued to be supplied with 120:208 Volt power.
I don't see a problem with your plan. (With the information provided)

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[simonfr]

Thanks waross

The main concern in the back of my mind and a throwaway comment given is that without the main winding operational, the tertiary may not function properly as the primary/secondary interaction is also required to help flux the primary/tertiary winding.

 

[waross]

If any winding is energized it will induce flux in the core.
If there is flux induced in the core, all windings will be energized.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Kiribanda]

It is a transformer with three windings. Once the high side is energized irrespective of whether 66-11kV is lightly loaded,
the 66-0.415kV side could be loaded provided the transformer is properly designed.

 

[dpc]

If the 415 V winding has a kVA rating, it should be able to carry power, regardless of loading or status of 11 kV winding. Check the nameplate. But to reiterate what the others have said - if any one winding is energized, all three windings will have voltage at the transformer terminals. Stay safe.

 

[prc]

You can load the secondary and tertiary in any way to their maximum ratings as per the rating plate. Usually, stabilising tertiary will be with a

​

1/3 rating of other windings. The only restraint is that the total of kVAs of secondary and tertiary shall not exceed the kVA of the primary winding.