Current Transformer Specifications

Here is some information you find of value on the specifications of CTs.

https://electrical-engineering-portal.com/learn-how-to-specify-current-transformers

The CT secondary resistance is specified to ensure that at a fault of x times nominal current the CT secondary current will reflect the x times primary fault current without saturating or failing to be able to drive the secondary current into the protection devices. If a fault of 20 times normal current flows in the primary then the protection CT must be capable of delivering 20 times current into the protection relay to drive the relay to trip in a proportionally shorter time.

Normally by specifying the class and type of CT as well as the working voltage, Primary and secondary current, accuracy, then the manufacturer will provide the correct CT.

However one should always test the CT for compliance to the values as it is not unheard of to find out of spec items supplied. I worked in a test and compliance section for a number of years and every CT, meter and relay was tested before installation and there were rejections for non compliance.