The secondary parameters of the current transformer include the ratio and accuracy level. For protection current transformers, the accuracy level is nominally expressed as a percentage of the maximum allowable compound error at the nominal accuracy of the primary current at the rated accuracy limit, followed by a "P" for protection. Rated Accuracy Limit Primary current refers to the maximum current indicated by the current transformer that can guarantee that the compound error does not exceed the allowable value of the accuracy class. Generally, it is marked by the accuracy limit coefficient. The rated accuracy limit coefficient is generally after its accuracy level. Marked; the so-called rated accuracy limit coefficient refers to the ratio of the rated current limit to the rated primary current. Ratio: It represents the ratio of primary current to secondary current, and is an important parameter for relay protection calculation and measurement. For the selection of the ratio, firstly, the indication accuracy of the measuring instrument under the rated working condition and the requirements of the rated input current and working accuracy of the protection device should be considered. For example, when the rated input current of the protection device is 5A, under normal operating conditions, the secondary output current of the current transformer of the measurement stage should be between 1 and 4.5A. If it is too small, (such as less than 0.5A) it is not reasonable. The protection level of the current transformer, because it is guaranteed to be unsaturated in the event of a system failure, the general ratio is greater than the current transformer ratio of the measurement stage. Note that the primary winding of the current transformer doubles the constant capacity of the series to the same ratio; the parallel ratio is doubled and the capacity is constant. The secondary winding has the same series ratio and the capacity is doubled; the parallel ratio is reduced by half and the capacity is unchanged. Accuracy level: At present, there are six accuracy levels of current transformers used in China: 0.1, 0.2, 0.5, 1, 3, and 5. According to the two types of measurement, measurement and protection, the measurement and measurement class needs to be accurately measured during operation to meet the measurement requirements under normal load, and the protection class is protected in the fault state to meet the requirements under the limit conditions. Accuracy of measurement and measurement: 0.1, 0.2, 0.5, etc. For example, 0.5 indicates that the current transformer's transmission error is not more than 0.5% under rated conditions. Protection accuracy level: generally adopts P level, for example, 5P20, which means that the error is 20% under 20 times rated current, so the protection level is not as accurate as the measurement measurement level, but has strong anti-saturation ability. Therefore, the winding of CT cannot be used incorrectly, otherwise it will be prone to saturation. For the relay protection part, it will be mis-operated or rejected. (The differential protection is easy to be mis-operated because the detection difference is too large. The backup protection will be too small because the acquisition value is too small. There is a case of refusal). Led Wall Lamp,Outdoor Wall lighting,High Quality Wall Lamp Kindwin Technology (H.K.) Limited , https://www.ktlleds.com