What factors affect the error of a molded current transformer?
2023-01-09
Cast resin current transformer What factors affect the error of a cast resin current transformer?
I. Internal parameters of the cast resin current transformer are the main factors causing errors.
1. The internal resistance R2 and leakage reactance X2 of the secondary coil have a great influence on the error. If R2 increases, the ratio error and phase angle error will also increase. When X2 increases, the ratio error will increase, but the phase angle error will decrease. To reduce the error value, it is necessary to reduce the values of R2 and X2.
The internal resistance R2 and leakage reactance X2 of the secondary coil are much smaller than the values of the secondary load RFH and XFH, so the values of R2 and X2 have little effect on the error, but the effect is obvious for small-capacity transformers.
2. Reducing the magnetizing current can effectively improve the ratio error and phase angle error. If there is no compensating transformer, the magnetic flux density of the iron core is relatively small, and as the magnetic flux density decreases, the magnetic permeability will also decrease. Even if the magnetizing current is not reduced much, the impact on the magnetic flux density will be greater.
3. The influence of the number of turns of the coil on the error. The number of turns of the coil needs to be increased, and increasing the number of turns can reduce the magnetic flux density, thereby improving the error. As the number of turns of the coil increases, the amount of copper used will also increase, leading to a decrease in the dynamic stability coefficient and an increase in the saturation coefficient.
4. Reduce iron loss and improve magnetic permeability. Under the premise that the magnetic flux density of the iron core remains unchanged, the reduction of the magnetizing ampere-turns and loss ampere-turns of the iron core will improve the ratio error and phase angle error. Using magnetic materials and selecting appropriate annealing processes can effectively improve the magnetic permeability and reduce losses.
II. Errors caused by the operation process of the cast resin current transformer
After the transformer is finalized, the internal parameters have been determined, and the error will be affected by the secondary current, secondary load, power factor, and frequency. These factors are also manifestations of external factors.
1. The error caused by changes in current frequency is complex. If the frequency change is too large, the error caused by the frequency must be considered. Changes in frequency will not only affect the loss and magnetic flux density of the iron core, but also the reactance value of the secondary load.
2. When the primary current decreases, the magnetic flux density will also decrease proportionally.
3. Once the power factor of the secondary load increases, the phase angle error will also increase, but the ratio error will decrease. In terms of saturation factor, a power factor of 0.8 is generally required. If the power factor increases or decreases, the saturation factor will increase.
Therefore, the influence Cast resin current transformer The factors affecting the error are mainly manifested in two aspects. After knowing the error, how to reduce it? We found that the magnetizing current is the main factor that causes the error to increase, so the error can be reduced by reducing the magnetizing current, such as increasing the cross-sectional area of the iron core, shortening the magnetic path length, selecting high-permeability materials as the iron core, limiting the secondary load, and appropriately increasing the transformation ratio, etc.
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