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The internal parameter of current transformer is the main factor that affects the error of current transformer.
Jul 08, 2017

The internal parameter of current transformer is the main factor that affects the error of current transformer.

The two secondary coil resistance R2 and leakage effects of anti X2 on error: with the increase of R2 ratio and angle difference increased; the increase of X2 ratio difference increases, but the angle of subtraction to improve the school and therefore should try to reduce the error of R2 and the value of X2. Because of the two coil internal resistance, R2 and leakage reactance X2, compared with the two load Rfh and Xfh, the value is very small, so the change of R2 and X2 has little effect on the error, only the small capacity current transformer is more significant.

The effect of error: the cross section of the iron core magnetic flux density increase core core section is reduced, the excitation current is reduced, thereby improving the ratio difference and angle difference. No flux current transformer compensation under rated condition of the iron core is very small, so reduce the magnetic flux density is relatively reduced the magnetic permeability, the excitation current is reduced, and the smaller the worse effect of magnetic flux density.

The effects of coil number of error: increase the number of turns of the coil is increased to increase the number of turns of the ampere turns, magnetic flux density decreases, the improved error effect than increasing the cross section of the iron core is more remarkable. However, the increase of coil turns will lead to an increase in the amount of copper and a decrease in the dynamic stability and an increase in the saturation factor. In addition, for a single turn type of current transformer (such as a core or bushing type current transformer, the primary coil is allowed only one turn), the method of increasing the number of turns can not be used to improve the error.

The reduction of iron loss and improve permeability. In core flux density under the same conditions, reduce core excitation and loss of ampere turns will also improve the ratio and phase error, so the magnetic material quality and adopt suitable annealing process can improve permeability and reduce the loss to the. The magnetic properties of the iron core also affect the saturation times. When the iron core is magnetic, the saturation times are relatively small

3.2 the error of the current transformer in operation

When the current transformer has been set, its internal parameters are determined, then its error size will be affected by two current (or primary current), two load, power factor and frequency. These factors are called external factors, and the error of the current transformer in operation is mainly affected by these four factors.

The influence of the current frequency change of error is more complex, the general system frequency change is very small, its influence can be neglected. If the frequency change is too large, such as the system of rated frequency 50Hz current transformer for 60Hz, we should consider the influence of frequency, because the frequency changes not only affect the iron loss and magnetic flux density and the size of coil leakage resistance, but also affect the two side load reactance.

When the primary current is reduced, the magnetic flux density proportionally reduced, but in low flux density, reduce excitation was slower than the magnetic flux density decreases, so the ratio and the absolute value of the angle difference is greater.

It has the following characteristics: the error of current transformer when a current change within the prescribed limits, two times the current change in proportion to two, when the load impedance within the prescribed scope changes, does not affect the two current. So when the two load reduction in the rated range, the magnetic flux density is reduced. Due to the same two current, excitation current is reduced, the error will be reduced current transformer factory specifications will generally indicate the rated load impedance value of two times, in the operation of the error should be given according to the connection mode of two of the biggest load impedance to check.

The power factor is two times the load is increased, Rfh increased, Xfh decreased and the angle difference will increase and will reduce the difference. For multiple saturation, saturation multiple transformer manufacturer specification stated refers to the power factor for the saturation ratio of 0.8, this value is equivalent to the saturated multiples of the minimum value, so the power factor either increases or decreases, the increase of saturation ratio.


Add: No.38 South Taoyuan Road, Yaozhuang Town,Jiashan County, Jiaxing City, Zhejiang Province, China
Contact person: Elva Zhuang&Sunny Ni
Tel:+86-573-84775555
Fax:+86-573-84776699
Phone:+86-13732570078
E-mail:sales9@great-relay.com
sunny.ni@great-relay.com