Current transformer iron core saturation problem analysis
2019 - current transformer iron core saturation problem analysis
30 15:05:36 current transformer error is mainly caused by the excitation current of Ie.
Normal run time due to large excitation impedance, therefore, Ie is very small, so that this error is negligible.
But when CT saturation, the more serious the degree of saturation, the smaller the excitation impedance, excitation current increases greatly, make the error of the transformer increases exponentially, affect the protection of right of action.
Serious when they make a current full excitation current, the cause of the secondary current is zero.
The causes of transformer iron core saturation for current or current commonly contain plenty of aperiodic component, both of which occurred in case of accident, at that time was to ensure proper protection action quick removal of fault, but if the transformer iron core saturation is easy to cause excessive error cause the incorrect action of protection, further affect system security.
So for current transformer iron core saturation problem we must take seriously.
Transformer iron core saturation problem if a detailed analysis is very complicated, so here is only for qualitative analysis.
We know that can pass the variable current transformer, it is the primary current produced flux in the core, and then in the wound in the same core of secondary winding electromotive force U = 4.
, a frequency f system in HZ,
N as the secondary winding circle number;
S for the core area, the m2;
B for the magnetic flux density in the core.
If the secondary circuit is a path, will produce the secondary current, complete the change of current in a secondary winding.
And when the magnetic flux density in the core after reaching saturation point, along with the change of exciting current or magnetic field strength B is not obvious.
That is to say in the N, S, f certain circumstances, secondary induction electric potential will be basic remain unchanged, so the secondary current will basically remain unchanged, a secondary current in proportion to the change of characteristic changes.
We know the transformer core is the core of the nature of the saturation magnetic flux density B is too large, more than the saturation point.
And flux in the core of how much decided to establish the size of the magnetic flux of current, which is the size of the excitation current of Ie.
When too much cause magnetic flux density is too large, Ie will make iron core tends to saturation.
While the transformer excitation impedance will drop significantly, resulting in the increase of exciting current again, and he intensified with the increase of the flux and the saturation of iron core, it is actually a process of a vicious cycle.
We can see from figure 1, the decrease of the Xe and the increase of the Ie, will show the current transformer error increases, so that affect the normal work.
Current transformer saturation of iron core in general can be divided into two cases to get to know.
One is the steady state saturation, and the other for transient saturation.
For the steady state saturation, can know from the above analysis, Internet explorer and secondary current Is in proportion to the shunt relationship.
Assuming excitation impedance Ze remains the same.
When a current due to reasons such as accidents, Ie is bound to be in proportion to increase, so the current transformer core flux increased.
If the primary current is too big, can also cause Internet explorer is too large, which will into what we call the above circulation, causing the transformer iron core saturation.
Transient saturation, it is to point to occur in the process of fault transient, caused by the transient component of transformer iron core saturation.
As we know, any fault occurs, the electric parameters are not mutations.
The occurrence of failure quantity is bound to be accompanied by more or less aperiodic component.
And aperiodic component, especially the direct current component of fault current is not in a transformer secondary transfer between change.
All these electrical flow will appear as excitation current.
So when the accident happened with larger transient component, also can cause the increase of excitation current, resulting in the transformer iron core saturation.