Current Transformer

Depending on the ultimate clients requirement, there are two main standards to which current transformers are designed. IEC 60044-1 (BSEN 60044-1) & IEEE C57.13 (ANSI), although the Canadian & Australian standards are also recognised.

Accuracy class: In the case of metering CT s, accuracy class is typically, 0.2, 0.5, 1 or 3. This means that the errors have to be within the limits specified in the standards for that particular accuracy class. The metering CT has to be accurate from 5% to 120% of the rated primary current, at 25% and 100% of the rated burden at the specified power factor.

From

http://en.wikipedia.org/wiki/Current_transformer

For the IEC standard, accuracy classes for various types of measurement are set out in BSEN /IEC 60044-1, class 0.1, 0.2s, 0.2, 0.5, 0.5s, 1 & 3. It will be seen that the class designation is an approximate measure of the accuracy, e.g., class 1 current transformers have ratio error within 1% of rated current class 0.5 within a ratio error of 0.5% etc.

From

http://www.kappaelectricals.com/technical.html

enjoy.

Class related to accuracy

There are 2 ANSI accuracy classes: 1) Metering accuracy 2) relaying accuracy.

Eg Metering accuracy= 0.3 B 0.2 where 0.3 is max ratio error %, B for burden (load), 0.2 (ohms allowed for metering to meter correctly)

Eg Relaying accuracy= 10 C 800 where 10 is max ratio error at 20 times rated current, C for low leakage unit, 800 is max sec voltage at 20* rated current.

Class is important to choose CT for corresponding application.

For additional help, see the previous discussions:

http://cr4.globalspec.com/thread/43440

http://cr4.globalspec.com/thread/49738

- MS