Current transformer's accuracy index

[Kaaud]

The accuracy-limit factor is the ratio between the accuracy-limit current and the rated
current.
For class P:
5P10 means 5% error for 10 In and 10P15 means 10% error for 15 In,
5P and 10P are the standard accuracy classes for protection CTs,
5 In, 10 In, 15 In, 20 In are the standard accuracy-limit currents.

what is accuracy limit current and what is In ?

 

[jim dungar]

what is accuracy limit current and what is In ?

In = Nominal (or nameplate) current rating

The accuracy current limit is point where the "error" is measured, this is used as an indication of how the sensor will respond to overloads.
5P10 = 5% error at 10x rated current.

 

[Kaaud]

In = Nominal (or nameplate) current rating

The accuracy current limit is point where the "error" is measured, this is used as an indication of how the sensor will respond to overloads.
5P10 = 5% error at 10x rated current.

10X ! thx thats what I missed

 

[Kaaud]

Why do u need accuracy when u interrupt a short circuit anyway ,what is the difference between 10% error for 10 In and 30% error in 10 In ,both are short circuits and both activates the Circuit breaker ,maybe u can get different short circuit current value on a digital multifunctional relay history?

 

[jim dungar]

Why do u need accuracy when u interrupt a short circuit anyway ,what is the difference between 10% error for 10 In and 30% error in 10 In ,both are short circuits and both activates the Circuit breaker ,maybe u can get different short circuit current value on a digital multifunctional relay history?

The CT's provide the input to the protective relays. If the input is not accurate then the protective devices may not operate as intended.