Causes of magnetic saturation of current transformer iron core
Causes of magnetic saturation of current transformer iron core - 2019
30 15:05:11 with the continuous development of power system, the relay protection and automation requirements of electrical equipment is higher and higher, the disadvantages of current transformer is exposed a serious, is the core problem of magnetic saturation.
In general core magnetic saturation is divided into two kinds: one kind is due to the steady state when short circuit current is too large, entered the current transformer saturation area, leading to secondary current cannot accurately reflect a current caused by saturation, called the steady state saturation;
Another kind is in short circuit current aperiodic component and remanent magnetization in core, makes the current transformer into saturated area caused by saturation, called transient saturation.
Factor in core into the saturation is 1, the influence of the dc component of core magnetic saturation if dc component existing in the current transformer primary winding and will make the magnetic flux has been increased, until it reaches saturation, at this time of the primary winding current will be used for field, current transformer secondary to 0, do not reflect the size of the primary current.
Thus, if the transformer primary side current of dc component, can make the flux increasing, and then enter the saturation.
2, the steady-state ac component of core magnetic saturation effect if a steady-state ac component is in the winding, as a result of the transformer magnetic chain in current positive and negative half cycle can always cancel each other out, will not continue to increase overall magnetic chain and saturation, but because of the short circuit current steady-state ac component existing in the high peak, transformer will be saturated when peak current, rendering the secondary current flat wave.
Because of current transformer saturation is mainly by the decaying dc component aperiodic established in transformer saturation magnetic flux, so a circuit time constant is also the important factors influencing the transformer saturation.
If a circuit time constant is larger, even if the short circuit current is not very big, the transformer will be saturated after growing a long enough time.
4, secondary side load impedance on the effect of magnetic saturation is applied to the relay protection of main work when the system short circuit current transformer, within the scope of the rated primary current, accuracy requirements is not high, but within the scope of the system short circuit current, its error less than 10%.
10% of the current transformer error curve is the system short circuit current and the ratio of the transformer rated current to the horizontal axis, with short circuit transformer and become error less than 10% of secondary side load impedance value of the vertical axis and draw the curve.
Therefore, the nature of the secondary side load impedance is one of the factors, which affect the current transformer saturation.
In the design of current transformer, in order to reduce transformer core loss at work, usually choose hysteresis loop narrower silicon steel sheet.
But this kind of silicon steel sheet remanence B1, generally is large, for there is no residual magnetism of silicon steel sheet, the core flux change in the range of 0 ~ saturation magnetic flux B2, and there is residual magnetism of magnetic flux in core range is only B = a B1 B2 obviously less flux range at this time.
Under normal working conditions of transformer core within the magnetic flux is small, usually does not cause saturation.
But when there is fault system, the transformer primary winding current will reach normal working current of dozens of times, and aperiodic fault current of dc component, will produce high magnetic flux in the core.
If the fault is removed, the magnetic flux in the core, exponential attenuation due to the normal working current is not very big, can't produce demagnetization effect to transformer, so if the short-circuit fault happening again, the remanent magnetism of magnetic flux in core will and short-circuit current aperiodic component of magnetic flux in the stack, fast into the iron core is saturated, so that the secondary side fail to reflect the situation of primary side short circuit current.
More than 4 o 'clock this causes the core factors leading to the magnetic saturation state, before processing to find out exactly what kind of situation is the saturated, and then suit the remedy to the case, not blindly.