Voltage transformer burden calculation

[MohamedIbrahim]

Dears, 

I'm working in a project and it's required to create VT calculation and We have the following issue:

The calculated burden is around 8 VA while the VT burden is 100VA and as per IEC 61869-3  clause number 5.6.301&302 it's mandatory to guarantee that the calculated burden of the VT is between 25% to 100% of the rated output burden.

The problem here that the VT is already purchased with VT burden 100VA, Thanks to advise about the accuracy?? or there is any solution for eradicate this problem without changing the Purchased VT.

[MathieuGuillot]

Hello

What are these VT used for ? 

You need accuracy for revenue metering but if the VT are only providing voltage measurement as a basic indication of for Over/undervotage protection the accuracy you have with a low burden is probably not an issue.

[RHH · Accepted solution]

I agree with @MathieuGuillot,

The IEC norm is probably used for measurements. As far as I know with measurements, you dont want to have a way lower output as it will influence your accuracy in measurement as the transformer is made for a certain use/output to measure most accurately.

For such specifics I use the internet for help, maybe the site beneath could help you relate better in what you want/need to do;

(Its for Power transformers, but might be usefull nonetheless)
https://www.electrical-installation.org/enwiki/Choice_of_transformer_rating

[MohamedIbrahim · Accepted solution]

Dear ,

I already find a solution by testing the accuracy of these VT's with the calculated burden in ALCE (VT supplier) and it's found that :

• SEE instruct their sub-supplier to test one 11 KV PT with a lower burden value of 3.75 VA (lower than 25% of the burden) and they found that the PT is in limits of Class1.0 at the test which is considered as a minor impact.

• SEE instruct their sub-supplier to test one 6.6 KV PT with a lower burden value of 8.35 VA (lower than 25% of the burden) and they found that the PT is in limits of Class1.0 at the test which is considered as a minor impact.

•the supplier confirmed that the protection core of all VT' will not be affected.

[RHH]

Hello @MohamedIbrahim,

Thats great to see, thanks for letting us know the road you've taken to your acceptable and on paper certified/calculated answer!

Good luck!

[EhabAbdou]

Hello @MohamedIbrahim 

I facing the same issue in substation, could you please advise if you have been solved this issue.

can you please if you have a solution contact me in eng.ehabmostafa@gmail.com 

[asif1]

True .... but the original VT was Class 0.2.  If its working accuracy is class 1, then its a loss.  Anyhow, it doesn't matter because nobody will look into design errors as long as there is no catastrophic failure....  Rest assured, in next project as well 100 VA VT will be procured