What is the accuracy of current transformers? How to classify?

Current transformers have accuracy levels of 0.2,0.5,1.0,3.0, and D.  The current transformers used for measuring and metering instruments are class 0.5 and class 0.2. Only the current transformers used for current and voltage measurement are allowed to use class 1.0. For non-important measurement, class 3.0 is allowed.  

1. Accuracy of current transformer for calibration: 0.1s, error 0.1%, often used to check the accuracy of current transformer of metering grade.  

2. Accuracy of current transformer for metering: 0.2s, 0.5s, error 0.2% and 0.5%, used for the basis of electricity bill settlement, also used in some occasions 0.5 level.  

3. Measuring grade current transformer: 0.5s, 1.0s, 2.0s, generally used for ammeter.  

Rated volt ampere, accuracy level and accuracy limit are three interdependent and inseparable technical parameters.  Generally speaking, the rated volt ampere refers to the maximum voltage the transformer can bear when the rated primary current guarantees a certain accuracy level.  Accuracy limit refers to the critical technical conditions that guarantee to maintain a certain degree of accuracy under rated load.  For example, the rated capacity of 15VA, the maximum allowed compound double error of 20 times the rated primary current is 10%, and the rated power factor is 0.8. The current transformer used for relay protection can be expressed as 15VA, cosφ=0.8,10P20, where P represents protection and 20 represents accuracy limit -- multiple of the rated current.  10 represents compound ratio error with accuracy level of 10%.