Cause Analysis of Current Transformer Error

(1) The influence of the internal resistance R2 of the secondary coil and the leakage reactance X2 on the error: when R2 expands, the ratio difference and angular difference increase; when X2 expands, the ratio difference expands, but the angular difference decreases, so the error should be improved as much as possible. Decrease R2 and moderate X2 values. Because the internal resistance R2 and leakage reactance X2 of the secondary coil are not large compared with the secondary loads Rfh and Xfh, the effect of changing R2 and X2 on the error is not great, only the small-volume current transformer has a greater impact. obvious.

(2) The influence of the iron core section on the error: the expansion of the iron core section reduces the magnetic flux density of the iron core and the excitation current, thereby improving the ratio difference and angle difference. The magnetic flux density of the iron core of the current transformer without compensation is already small under the rated value standard, so reducing the magnetic flux density also reduces the magnetic permeability index relatively, so that the excitation current does not decrease much, and the smaller the magnetic flux density is the worse the effect.

(3) The influence of the number of coil turns on the error: increasing the number of coil turns means increasing the ampere-turn. Increasing the number of turns can reduce the magnetic flux density, and the effect of improving the error is much more obvious than increasing the core section. However, the increase in the number of coil turns will result in an increase in the amount of copper, and at the same time, a decrease in the dynamic stability factor and an increase in the saturation state factor. In addition, for single-turn current transformers (such as through-core or bushing-type current transformers that only allow one turn in the primary coil), it is not possible to increase the number of turns to improve the error.

(4) Reduce core loss and improve magnetic permeability. Under the standard that the magnetic flux density of the iron core will not change, reducing the ampere-turn and loss ampere-turn of the core excitation regulator will also improve the ratio difference and angle difference, so the selection of high-quality permanent magnet materials and the use of suitable annealing processes can To achieve the purpose of improving permeability and reducing loss. The quality of the iron core with magnetism also affects the saturation state multiple, and the saturation state multiple is smaller when the iron core has a magnetic difference.