CT Saturation X/R Contribution Effect

[MeinKaun11]

Hi

I was trying to make a quick excel sheet where I could plug in some relevant information and get the secondary excitation voltage during a fault event and see if my CT accuracy selection is ok. Below is the link, I was using as a quide:

http://www.powellind.com/main/Uploadpdf/PCIC-2005-32 CT Saturation.pdf

But based above the guide CT's used for medium vol switch-gear applications would be very expensive considering the use of X/R ratio, which is actually (1+X/R) multiple to the symmetrical current voltage. It also says that IEEE has made it mandatory to use X/R ratio to be used as a sizing factor but never reached to a conclusion when the paper talks about the capability of digital relays to take distortion out during a saturated waveform situation.

Also on page 3, author comes to a conclusion that C200 600/5 is not good enough for the application since fault current is 30 times rather than 20 times. He does not talk about the requirement of 2 ohm burden but in this case the burden is .235 ohm, will that not increase the accuracy ?

Did I get this observation right ?

Appreciate your input.

 

[collies99]

The paper did the proper calculations based on the various formulae into the specified burden. The voltage answers are compared to the vsat rating of the specified CT curve which is at 2 ohm.

The accuracy does not change at or below the rated vsat value.

 

[MKFPE]

Why re-invent the wheel?

Search "ieee psrc ct saturation calculator"

for an excellent spreadsheet.

You can test various burden values and confirm your observation.

Regards,