Reasons that affect the error of the Electrical Current Transformer

1. The influence of the return conductor

In an ideal situation: the electrical current transformer's secondary winding wires are evenly distributed on the toroidal iron core,-the secondary winding is also evenly distributed or the primary winding is an infinite conductor and passes through the center of the iron core. The flux density is equal. In fact, there is a return conductor in the primary winding structure of the transformer itself (except for the inverted and penetrating transformers). For example, the high-voltage transformer uses a "U"-shaped primary winding with two leads, and the secondary winding is sheathed on one lead and the other The bow | wire and the loop (bend) conductor constitute the return conductor.

When the Electrical Current Transformer manufacturer analyzes the influence of the return conductor, take a simple return conductor that is parallel to the secondary winding conductor of the transformer as an example. Due to the magnetic flux generated by the current in the return conductor, the magnetic flux density of the iron core on the side close to the return conductor through the iron core increases, and the magnetic flux density of the iron core on the side far from the return conductor decreases, so that the magnetic flux density of the iron core grid segment is not Wait. Because most of the magnetic flux path generated by this external magnetic field passes through the air, the iron core magnetic circuit is only a very small section, so its magnetic induction intensity is proportional to the permeability of the air; and the magnetic field lines are only linked with part of the secondary winding, which is normal. In this case, it is the magnetic flux leakage that increases the secondary leakage reactance. However, in the case of a large overcurrent, the magnetic flux density of the core near the return conductor will increase rapidly, and the error will increase rapidly, especially for the electrical current transformer for protection, which may cause the compliance error to exceed the limit.

2, the dispersion of core excitation characteristics

In the case of the same rated ampere-turn, secondary load, core cross-sectional area, and wire, the measured error results are also different due to the different core excitation characteristics, and the difference is huge. The excitation current is the direct cause of the error. The smaller the excitation current, the smaller the current error; the larger the excitation current, the larger the current error.