Current Transformer Burden Calculation

This thread may help:

http://cr4.globalspec.com/thread/42970

- MS

Dear Engineer,

Thank you for your response. Actually, the rated burden of the CT is 15 VA for the tapping 1S1 - 1S4. But I want to calculate, the Burden for the tapping 1S1 - 1S2 AND 1S1 - 1S3.

Kindly clarify.

I feel the VA rating of the CT is same for all combinations. Because at each combination, the secondary current is same. So the VA remain same.

The rated Burden of any CT is the sum of its internal burden and the external burden. And the internal (VA) burden would remain constant as at lower tap ratios the number of secondary turns would also change, thereby changing the Ohmic burden of the CT Secondary winding.

For example, assuming a bar primary (single turn) in your case, at a ratio of 600/1A, the primary ampere-turns would be 600AT and to offset this, the CT secondary of 1A should have about 600 turns.

If the Primary Current is chosen as 300A, then the Primary AT would be 300AT and to balance out the CT Secondary (of the same 1A) would now have only 300 Turns. So, also in 150A Tap.

As you can see at lower tap ratios, the number of turns and hence the internal burden of the CT would reduce.

The CT burden is very important parameter for ensuring reliable protection operation. The CT can go into saturation if the burden on CT is more. The burden is expressed in ohm or in VA.

The infinite burden means CT is open circuited and core of the CT gets saturated. The CT burden is the sum of the resistance of CT secondary winding resistance,lead wire resistance and relay resistance. The Loose connection from CT secondary terminals to relay may also cause higher burden.

Read More:https://sdvelectrical.blogspot.com/2019/05/how-to-calculate-burden-of-ct.html

What do you want to convey? Did I anywhere say that burden is not important? Please do not try to educate me, unless I post a query.

Your points are well taken.