JPH038566B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a direct current sensing current transformer.

As shown in the first diagram, a gap 2 is provided in the middle of the circumference of the annular core 1, a Hall element 3 is inserted into the gap 2, and a direct current I _DC is passed through the electric wire 5 passed through the window hole 4 of the annular core 1. Constant control current I _C in Hall element 3
, a voltage V ₀ proportional to the direct current I _DC is obtained.

However, the value of the Hall voltage V ₀ when the DC current I _DC is increased and then lowered is different from the value of the Hall voltage V ₀ when the DC current I _DC is increased from negative through 0. . This is not so much of a problem when detecting a large value of direct current I _DC , but it becomes an error and becomes a problem when detecting a small value of direct current of several amperes or less. When I _DC = 0 and the output is 0, the relationship between I _DC and V ₀ is graphed as shown in Figure 2.

The present invention aims to provide a DC current detection current transformer that uses a pair of the above-mentioned annular cores and devises the arrangement of the cores and the connection of the coils wound around them, and is capable of accurately measuring DC current down to several milliamperes. That is.

An embodiment of the present invention will be described below based on FIGS. 3 to 5. Reference numerals 6 and 7 are a pair of annular cores, each having a gap 8 in the middle of its circumference, and near the gap 8, they contact each other. The other parts are arranged apart from each other. Excitation windings 9 and 10 are respectively wound around mutually distant parts of the annular cores 6 and 7, and are connected so that the magnetic fluxes φ _A and φ _B are added. When connected in this manner, the cores 6 and 7 from the excitation windings 9 and 10 become a non-divided core, and the core is saturated with a small excitation current. Reference numeral 11 designates a power source connected to cause an alternating current or direct current to flow through the excitation windings 9 and 10, 12 a Hall element placed in the air gap 8, and 13 an electric wire passed through the window hole 14 of the iron cores 6 and 7.

In the above configuration, a direct current I _DC is applied to the electric wire 13,
That is, while passing the primary current, the excitation windings 9,
An excitation current is applied to the hall element 10 by pulses once every few seconds until the iron cores 6 and 7 are saturated, and a control current I _C =5 mA is applied to the hall element 12.

From the perspective of the primary current, one core is in the direction in which magnetic flux is added, and the other core is always in the direction in which it is demagnetized. Since the magnetic fluxes generated by the excitation windings of the iron cores 6 and 7 are equal, no flux flows through the Hall element 12 at all. Therefore, the Hall voltage V ₀ is not generated by the magnetic fluxes φ ₁ and φ ₂ caused by the excitation windings 9 and 10, but the Hall voltage V ₀ is generated only by the primary current.
Since the magnetic flux φ ₁ generated by the excitation winding 9 is equal to the magnetic flux φ ₂ generated by the excitation winding 10, the magnetic flux φ ₁ passes through the part where the iron cores 6 and 7 are in contact, and the magnetic flux φ ₂
All go to. Therefore, since a pulse or alternating current is applied with an excitation current higher than the residual magnetism, there is no change in the Hall voltage V ₀ due to the influence of the residual magnetism. Comparing the values at that time, A before the excitation current is passed through the excitation windings 9 and 10, and B when the excitation current is passed, the results are as shown in the graph in Figure 5. It can be seen that while there is a considerable error in the Hall voltage in the former case, there is almost no error in the latter case.

Since the present invention is configured as described above, it is possible to provide a DC current detection current transformer that can accurately measure DC current up to several milliamperes.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of detecting DC current using one ring-shaped iron core, Fig. 2 is a graph showing the Hall voltage error in the same example, and Fig. 3 is a diagram showing the principle of the DC current detection current transformer according to the present invention. Fig. 4 is a plan view showing the principle of the current transformer, and Fig. 5 is a graph showing a comparison of the Hall voltage before and when excitation current is applied to the current transformer. be. 6, 7...Pair of annular cores, 8...Gap, 9,
10... Excitation winding, 12... Hall element.

Claims (1)

[Claims] 1. A gap is provided in the middle of the circumference of the annular core, and a pair of the annular cores are placed in contact with each other near the gap, and are spaced apart from each other in other parts, A coil is wound around each part, and these coils are connected so that the magnetic flux is added, and a Hall element is inserted into the gap between the pair of annular cores to create a DC current detection current transformer that compensates for residual magnetism. .