JP2012198158A - Current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current sensor capable of securing measurement accuracy by suppressing magnetic saturation in current measurement and capable of reducing size and cost.SOLUTION: A current sensor 1 includes an iron core part 102 formed like a circular shape to collect magnetic flux generated by a primary current flowing into a current line 101 to be measured which is arranged through the center part of the circular shape and winding 103 wound around the iron core part 102 in a toroidal direction to detect a magnetic flux change in the iron core part 102 and is configured to measure the primary current from an output of the winding 103. The iron core part 102 includes a core division area Km in which a plurality of grooves 107 are arranged along the toroidal direction and a core connection area Ks connected in the toroidal direction. In the core division area Km of the iron core part 102, a ratio of a cross section of the iron core part 102 to a cross section of the groove 107 in a section of a diameter direction is fixed over a toroidal circumference.

Description

  The present invention relates to a current sensor that measures a current flowing through a conductor.

  In the conventional current sensor, when the current to be measured increases, the iron core is magnetically saturated, and the current value cannot be measured accurately. Therefore, in order to measure a large current, it is necessary to increase the volume of the iron core and the cross-sectional area through which the magnetic flux passes so that the iron core is not magnetically saturated. However, the current sensor is increased in size and weight.

  In order to reduce the size and weight of such a current sensor for measuring a large current, a method is conceivable in which the iron core is divided and the magnetic flux penetrating the iron core is reduced to prevent magnetic saturation so that the iron core does not become magnetically saturated. For example, it has been proposed to use an iron core portion in which iron-based powder and non-magnetic powder are mixed and hardened (for example, Patent Document 1). In addition, it has been proposed to ensure measurement accuracy by forming a shape in which an iron portion and a nonmagnetic portion are uniformly arranged (for example, Patent Document 2).

Japanese Patent Laying-Open No. 2006-24844 (FIG. 2) Japanese Patent No. 4499707 (FIG. 1)

  The current sensor as in Patent Document 1 uses a mixed magnetic core of magnetic material and non-magnetic material, but the location of iron and the location of non-magnetic material are indefinite, so the magnetic flux density locally increases. Not uniform. As a result, the number of magnetic fluxes interlinking the windings varies depending on the location, so that a phenomenon occurs in which some portions are magnetically saturated and other portions are not magnetically saturated. Therefore, the accuracy of linearity with respect to the current line to be measured is lowered. In addition, if the saturation characteristics of the iron core are uniform over the entire circumference and the winding is wound uniformly over the entire circumference, the influence can be canceled even if a disturbance magnetic field occurs. However, there is a problem that if it differs depending on the location, it cannot be canceled and the measurement accuracy is lowered.

  In addition, the current sensor as in Patent Document 2 can uniformly arrange the iron core, so that the measurement accuracy can be ensured. However, if the position of the iron core and the non-magnetic material is arranged with high accuracy, the manufacturing cost tends to increase. .

  An object of the present invention is to provide a current sensor that can ensure measurement accuracy by suppressing magnetic saturation during current measurement, and can be reduced in size and cost.

In order to achieve the above object, the present invention is formed in an annular shape, and an iron core portion that collects magnetic flux generated by a primary current flowing through a primary conductor disposed through a central portion thereof,
It is wound in the poloidal direction with respect to the iron core, and includes a winding for detecting a magnetic flux change in the iron core,
A current sensor for measuring the primary current from the output of the winding,
The iron core part includes a core division region in which a plurality of grooves are arranged along the toroidal direction, and a core connection region connected in the toroidal direction,
In the core divided region of the iron core, the ratio of the cross-sectional area of the iron core to the cross-sectional area of the groove in the radial cross section is constant over the entire toroidal circumference.

  According to the present invention, when magnetic saturation occurs in the core connection region during current measurement, the core division region mainly functions as an iron core. Therefore, the magnetic flux density in the iron core is reduced, the primary current that causes magnetic saturation can be increased, and the magnetic flux density in the winding cross section is made uniform, so that measurement accuracy can be ensured. Further, when the iron core portion is formed as a single member, it can be easily manufactured, and a highly accurate current sensor can be realized at low cost.

It is a perspective view which shows the current sensor by Embodiment 1 of this invention. It is a top view of the current sensor shown in FIG. It is a top view of the iron core part shown in FIG. It is an enlarged view of the A section in FIG. It is explanatory drawing which represented the mode of the magnetic flux in an iron core part typically. It is explanatory drawing which represented the mode of the magnetic flux in an iron core part typically. It is a graph which shows an example of the output characteristic with respect to to-be-measured current about a current sensor. It is a top view which shows the other example of an iron core part shape. It is a top view which shows the other example of an iron core part shape. It is a fragmentary top view which shows the iron core part of the current sensor by Embodiment 2 of this invention. It is a perspective view which shows the current sensor by Embodiment 3 of this invention. It is a perspective view which shows the other example of a bias magnetic field application mechanism.

Embodiment 1 FIG.
FIG. 1 is a perspective view showing a current sensor 1 according to Embodiment 1 of the present invention. The current sensor 1 includes an iron core portion 102, a winding 103, and the like. The iron core portion 102 is made of a magnetic material formed in an annular shape, and its radial cross section has, for example, a rectangular shape or a rounded corner rectangular shape. The current wire to be measured 101 is arranged as a primary conductor so as to penetrate the central portion of the iron core portion 102. When the primary current flows through the measured current line 101, a magnetic flux 104 is generated around the current line 101, and the iron core 102 collects the generated magnetic flux 104.

  The winding 103 is wound in the poloidal direction around the annular iron core portion 102 and has a function of detecting a magnetic flux change in the iron core portion 102 as a secondary winding. For example, a burden resistor 105 is connected to both ends of the winding 103. When the magnetic flux 104 changes with time due to an alternating current flowing through the current wire 101 to be measured, an induced current is generated in the winding 103 accordingly. Therefore, by measuring the voltage across the load resistor 105 using an external measuring instrument, the amplitude, frequency and phase of the primary current flowing through the current line 101 to be measured can be measured. Such a current sensor 1 can operate as a current transformer (CT), for example.

  FIG. 2 is a plan view of the current sensor 1 shown in FIG. FIG. 3 is a plan view of the iron core portion 102 shown in FIG. FIG. 4 is an enlarged view of a portion A in FIG. The measured current line 101 extends in the direction perpendicular to the paper surface and passes through the center of the annular iron core 102. The winding 103 is wound around the annular core 102 in the poloidal direction.

  The iron core portion 102 includes a core division region Km in which a plurality of grooves 107 are arranged along the toroidal direction, and a core connection region Ks connected in the toroidal direction. In the core division region Km, the groove 107 is formed in a cut shape from the outer side to the inner side of the iron core part 102 so as to obliquely intersect the radial direction of the iron core part 102, and an air gap between adjacent iron parts 106. Function as. On the other hand, in the core connection region Ks, the groove 107 does not exist, and the iron portions 106 are integrally connected.

  Here, as shown in FIG. 4, focusing on a certain groove 107, the distance from the inner edge of the core division region Km to the inner edge of the groove 107 in the radial cross section is c1, the gap length of the groove 107 is g, and the groove Let c2 be the distance from the outer edge 107 to the outer edge of the core division area Km. Further, paying attention to another groove 107, the distance from the inner edge of the core split region Km to the inner edge of the groove 107 in the radial section is c1 ′, the gap length of the groove 107 is g ′, and from the outer edge of the groove 107. Let c2 ′ be the distance to the outer edge of the core division area Km. At this time, g: (c1 + c2) = g ′ :( c1 ′ + c2 ′) is established.

  In other words, in the core division region Km of the iron core portion 102, the ratio of the cross-sectional area of the iron core portion 102 to the cross-sectional area of the groove 107 in the radial cross section is constant over the entire toroidal circumference. Such a component shape can be formed, for example, by pressing a plate-shaped iron material at a time by pressing or the like, so that high dimensional accuracy can be realized at a low manufacturing cost.

  Next, the operation of the current sensor 1 will be described. When a current flows through the current wire 101 to be measured, the magnetic flux passes in the toroidal direction inside the iron core portion 102.

  5 and 6 are explanatory diagrams schematically showing the state of magnetic flux in the iron core portion 102. FIG. Here, the density of the arrows corresponds to the magnetic flux density. When the current flowing through the measured current line 101 is small, as shown in FIG. 5, the magnetic flux mainly flows through the inner core connection region Ks. At this time, magnetic saturation does not occur because the magnetic flux is low. Therefore, similarly to the operation of a normal current transformer, a change in magnetic flux passing through the iron core 102 is output as an induction current of the winding 103 as it is.

  Next, when the current value of the current wire 101 to be measured increases, as shown in FIG. 6A, most of the magnetic flux passing through the iron core portion 102 further passes through the inner integrated core connection region Ks. Thus, only the core connection region Ks becomes magnetically saturated. The magnetically saturated portion has a reduced magnetic permeability, and when fully saturated, the magnetic permeability is almost equal to that of air. As a result, the region having high magnetic permeability, that is, the effective core region is only the core division region Km excluding the core connection region Ks, as shown in FIG. This state is equivalent to a split iron core positioned with high dimensional accuracy. In this state, even if the current to be measured becomes large, the effective core region functions in the same way as the divided core, so magnetic saturation due to the air gap can be suppressed, and accuracy can be achieved even with a large current. It can be measured well.

  FIG. 7 is a graph showing an example of output characteristics with respect to the current to be measured for the current sensor 1. In the small current range from the current to be measured starting from zero to the current value I1 at which the core connection region Ks is magnetically saturated, nonlinear characteristics are shown. On the other hand, when the current value exceeds I1, the core divided region Km functions as a divided iron core, and thus it can be seen that linearity is ensured over a wide current range. Therefore, by setting the measurement range of the current sensor 1 to the range from the current value I1 to the current value I2 in which the core division region Km itself indicates magnetic saturation, it is possible to ensure a high measurement accuracy that can sufficiently withstand practical use. In addition, since the iron portion 105 of the iron core portion 102 can be obtained with good dimensional accuracy at low cost by pressing or the like, the output linearity is high and the resistance against the disturbance magnetic field is also high.

  In order to facilitate magnetic saturation, the core connection region Ks desirably has the smallest possible width and cross-sectional area of the area through which the magnetic flux passes. As shown in FIG. 4, in the radial cross section, the width of the core connection region Ks is a, the width of the core division region Km is b, and the width a is 10% or less of the width b (0 <a / b ≦ 0.1). It is preferable that In terms of the cross-sectional area through which the magnetic flux passes, the cross-sectional area Sa of the core coupling region Ks in the radial cross-section is 10% or less (0 <Sa / Sb ≦ 0.1) of the cross-sectional area Sb of the core divided region Km. Preferably there is. Thereby, even if the current to be measured is small, the magnetic saturation is likely to occur, and the current value I1 can be further reduced in the graph of FIG. 7, so that the current measurement range can be expanded.

  In the present embodiment, as illustrated in FIGS. 2 to 4, the case where the core connection region Ks is disposed inside the iron core portion 102 and the core division region Km is disposed outside the iron core portion 102 is illustrated. Alternatively, as shown in FIG. 8, the core division region Km may be disposed inside the iron core portion 102, and the core connection region Ks may be disposed outside the iron core portion 102. Moreover, as shown in FIG. 9, the core connection region Ks may be disposed inside and outside the iron core portion 102, and the core division region Km may be disposed between the two core connection regions Ks. Moreover, although not shown in figure, the core division | segmentation area | region Km may be arrange | positioned at the inner side and the outer side of the iron core part 102, respectively, and the core connection area | region Ks may be arrange | positioned between the two core division areas Km.

  According to the present embodiment, when magnetic saturation occurs in the core connection region Ks during current measurement, the core divided region Km functions as a divided iron core. Therefore, the magnetic flux density in the iron core is reduced, the primary current that causes magnetic saturation can be increased, and the magnetic flux density in the winding cross section is made uniform, so that measurement accuracy can be ensured. Further, when the iron core portion 102 is formed as a single member, the manufacturing becomes easy, the manufacturing process is simplified, and a highly accurate current sensor can be realized at low cost.

Embodiment 2. FIG.
FIG. 10 is a partial plan view showing the iron core portion 102 of the current sensor 1 according to the second embodiment of the present invention. The present embodiment has the same configuration as that of the first embodiment, but is different in that the magnetic path is lengthened and the magnetic resistance is increased in the core connection region Ks.

  In the core connection region Ks, a plurality of grooves 107 are arranged in a cross finger shape and have a shape of a fold line (so-called meander line) 108. With such a structure, when the magnetic flux passes through the core coupling region Ks, the cross-sectional area through which the magnetic flux passes is smaller than in the first embodiment, and the distance through which the magnetic flux passes increases. Magnetic saturation level is lowered. As a result, even if the current to be measured is small, it is easy to saturate, and the current value I1 can be made smaller in the graph of FIG. 7, so that the current measurement range can be expanded and a wide range current sensor can be realized.

Embodiment 3 FIG.
FIG. 11 is a perspective view showing a current sensor 1 according to Embodiment 3 of the present invention. The present embodiment has the same configuration as that of the first embodiment, but is different in that a bias magnetic field application mechanism for applying a toroidal bias magnetic field to the iron core portion 102 is provided.

  In FIG. 11, as a bias magnetic field application mechanism, a current line 109 separate from the current line 101 to be measured is arranged in parallel with the current line 101 to be measured. Both ends of the current line 109 are connected to a current source (not shown). When a predetermined DC current flows through the current line 109, a DC bias magnetic field is generated in the toroidal direction of the iron core portion 102. As a result, the bias magnetic field generated by the current line 109 is superimposed on the magnetic field generated by the current line 101 to be measured inside the iron core portion 102. As a result, the magnetic field at which the core coupling region Ks of the iron core portion 102 reaches magnetic saturation is reduced. In other words, the core connection region Ks is easily magnetically saturated even if the current value of the measured current line 101 is small. As a result, even if the current to be measured is small, it is easy to saturate, and the current value I1 can be made smaller in the graph of FIG. 7, so that the current measurement range can be expanded and a wide range current sensor can be realized.

  FIG. 12 is a perspective view showing another example of the bias magnetic field applying mechanism. As a bias magnetic field applying mechanism, a winding 110 separate from the winding 103 is wound around the annular core 102 in the poloidal direction. Both ends of the winding 110 are connected to a current source 111, and when a predetermined DC current flows through the winding 110, a DC bias magnetic field is generated in the toroidal direction of the iron core portion 102, as in FIG. As a result, the magnetic field at which the core connection region Ks of the iron core portion 102 reaches magnetic saturation is reduced, and the current value I1 can be further reduced in the graph of FIG. 7, so that the current measurement range can be expanded and a wide-range current sensor is realized. it can.

  11 and 12, the bias magnetic field superposition by the additional installation of the current line has been described. Alternatively, the toroidal bias magnetic field may be superposed by the additional installation of an electromagnet or a permanent magnet. .

  The bias magnetic field application direction is preferably the toroidal direction of the iron core portion 102 as shown in FIGS. 11 and 12, but is not limited to this, and it is sufficient if the core connection region Ks is magnetically saturated. There is no particular restriction on.

1 current sensor, 101 current wire to be measured, 102 iron core, 103 windings,
104 magnetic flux, 105 burden resistance, 106 iron part, 107 groove,
108 fold line, 109 current line for applying bias magnetic field,
110 Bias magnetic field application winding, 111 Current source, Km core split region,
Ks Core connection region.

Claims (5)

An iron core that collects magnetic flux generated by a primary current that flows through a primary conductor that is formed in an annular shape and passes through a central portion thereof;
It is wound in the poloidal direction with respect to the iron core, and includes a winding for detecting a magnetic flux change in the iron core,
A current sensor for measuring the primary current from the output of the winding,
The iron core part includes a core division region in which a plurality of grooves are arranged along the toroidal direction, and a core connection region connected in the toroidal direction,
A current sensor characterized in that a ratio of a cross-sectional area of a core part and a cross-sectional area of a groove in a radial cross section is constant over the entire toroidal circumference in a core division region of the iron core part.   The current sensor according to claim 1, wherein the core connection region is disposed on one or both of an inner side and an outer side of the iron core.   3. The current sensor according to claim 1, wherein a cross-sectional area of the core connection region is 10% or less of a cross-sectional area of the core division region in the radial cross section.   The current sensor according to any one of claims 1 to 3, wherein the core connection region has a shape of a folding line in which a plurality of grooves are arranged in a cross finger shape.   The current sensor according to claim 1, further comprising a bias magnetic field applying mechanism for applying a toroidal bias magnetic field to the iron core.

Images