JPH0242366A - Current detecting method and current detector - Google Patents

Abstract

PURPOSE:To accurately detect a low level current and to easily equip to a distribution line by detecting a current to be detected which is penetrates into an inside of its tube by a Rogowski coil. CONSTITUTION:A logousky coil 1 of a current detector K1 is constituted of a winding frame 2 formed of a flexible non-magnetic material like polyethylene, etc., bending like a circular ring, and an annular solenoid 3 which is winded in ring form so that the solenoid has a constant number of winding (n) per unit length corresponding to the winding frame 2 and the average section area S is constant in the axial direction of the winding frame 2. Further, by allowing the average section area S to be as small as possible and enlarging the number of winding (n) per unit length, thus permitting increment of an output voltage of the solenoid 3. Moreover, the cylindrical body 8 arranged flexibly interposing like a concentric circle against the Rogowski coil 1 is formed cylindrically of a magnetic material of a soft iron etc., and its thickness is set so that the magnetized current generated in the cylindrical body 8 is distributed actually only on the surface thereof corresponding to a permeability of the magnetic material in the tube 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current detection method and a current detector.

[Prior Art] CT has been proposed as a current detector, and an example of its application is a zero-sequence current detector (hereinafter referred to as ZCT). There is a problem with residual voltage. The residual voltage is an output generated in the current transformer secondary winding even if the three-phase load current interlinking with the ZCT does not include a zero-phase component, as if it were included.

In Japan's high-resistance grounded power distribution system, even if a ground fault occurs, the ground fault current is small, and its zero-sequence current remains at a low level. Therefore, when trying to detect a zero-sequence current using ZCT, the residual voltage becomes noise, significantly deteriorating the S/N ratio, and making detection virtually impossible.
It is impossible with a general ZCT to detect a ground fault current level of about 200 [mA] with respect to a load current of [A].

In order to solve this problem, conventional ZCTs wind a tape made of a good conductor such as copper or a magnetic material with high magnetic permeability over the secondary winding, or make the core magnetic path elliptical. Furthermore, the residual voltage is reduced by changing the number of turns of the secondary winding along the longitudinal direction of the core magnetic path. This actually reduces the residual voltage and the iron core Z
CT is actually used for zero-sequence current detection in power distribution systems.

However, the problem is that the proper way to wind the tape to reduce residual voltage, the desirable shape of the magnetic path, the necessary distribution of the secondary winding, etc. can only be obtained through trial and error and after gaining sufficient experience. there were.

This is considered to be because the cause of residual voltage generation is not necessarily clear physically or theoretically. Therefore, for example, it would be inconvenient for an equipment manufacturer to design and manufacture a ZCT based on general magnetic circuit theory, and that they would have to outsource this work to a specialized manufacturer.

Furthermore, since it is impossible to open the magnetic path of the completed iron core ZCT, the work of assembling the ZCT to the distribution line becomes troublesome, and there are practical problems in that the locations where the ZCT can be assembled are limited. There were also points. Similar problems as described above occur in CT.

[The problem that the invention tries to solve! ! ] This invention was made to solve the above-mentioned conventional problems, and in the case of zero-sequence current detection, it is possible to accurately detect low-level currents up to about 1/2000 of the load current. It can be designed and manufactured based on practical theory without relying on special know-how, and it can be easily installed on distribution lines, and in the case of load currents such as single-phase current. Another object of the present invention is to provide a current detection method and a current detector that can detect even minute load currents without being affected by unfavorable characteristics of the iron core, and that are flexible in terms of mounting locations.

[Means for Solving the Problems] In order to achieve the above object, a first invention provides a cylinder formed of a magnetic material having a thickness such that a magnetizing current generated from a current to be detected is distributed virtually only on the surface. On the outside of the body, a Rogowski coil is wound around the solenoid in an annular manner along its axial curve so that the average cross-sectional area and number of turns per unit length are constant, and the solenoid is penetrated into the inside of the cylindrical body. The gist of this is to detect the current to be detected.

A second invention is a current detector in which a Rogowski coil formed by winding a coil around a core material is made into a circular shape, and a conductor through which a current to be measured passes through the inside of the Rogowski coil is passed through, the outer periphery of the Rogowski coil being circular. The gist is that it is covered with a magnetic case.

The gist of the third invention is that the Rogowski coil is arranged at the center of the magnetic case.

[Function] According to the research conducted by the present inventors, it is believed that the main cause of the residual voltage is that the magnetic flux density generated in the ZCT iron core due to a healthy load current is non-uniform along its magnetic path. Iron cores are originally used for the purpose of eliminating such non-uniformity and creating a uniform magnetic flux density, and thus a constant magnetic flux, within the core magnetic path. However, the iron core material;
Magnetic flux flows in and out from the sides of the magnetic path due to linearity, local magnetic saturation, and magnetic flux density due to the image current on the iron core relative to the load current. Therefore, the magnetic flux linkage of the ZCT secondary winding is no longer directly proportional to the algebraic sum of the currents interlinked to the ZCT. This is thought to be the cause of the 4 lightning voltage occurrence.

Therefore, in the present invention, the current is detected using a Rogowski coil based on Ampere's circuit integral theorem.

As is well known, this theorem is based on H as a magnetic field, C as an arbitrary closed curve, and 1 t + as an algebraic sum of free currents (currents supplied from an external circuit excluding magnetizing currents generated in magnetic materials) interlinking with C. Then, it is written as . This equation holds true regardless of the presence or absence of a magnetic medium and its type. As a quantity proportional to the line integral in equation (1), the induced voltage of a ring solenoid, that is, a Rogowski coil, evenly wound in the axial direction of the coil is used. If the cross-sectional area of the coil is S, the vacuum permeability is μ0, and the normal vector to the area S is (//dA), then the magnetic flux inside S is μ.・5
When S is small enough to be regarded as rt-(H, the induced voltage in the Rogowski coil is . However, n is the number of turns per unit length in the axial direction of the coil, and μ is the vacuum permeability. From equations (1) and (2), the algebraic sum of the currents interlinking with the coil is given by: By integrating the induced voltage V over time, the algebraic sum of the currents can be found in principle. When the current is a sinusoidal alternating current, ■ and its time integral are also sinusoidal, and the current value is proportional to V. In such cases, only the relative value of the current is required, or the absolute value of the current is required. If it is possible to calibrate the values, the time integration in (2) can be omitted.

However, if the Rogowski coil described above is attached to a three-phase load current with it exposed, the residual voltage will be large and the detection of low-level zero-phase current will be difficult, as is the case with iron-core ZCTs that are not wrapped with copper tape or magnetic tape. is impossible.

Therefore, in the present invention, a cylinder made of a magnetic material is further interposed between the current to be detected and the Rogowski coil so as to surround this current. Furthermore, this cylinder includes a ring-shaped magnetic case made up of double cylinder elements and both ends of which are closed with a magnetic material, and a Rogowski coil is housed in the ring-shaped magnetic case, and the current to be detected is applied to the hollow part of the case. It may be passed through.

If the magnetic permeability of such a magnetic material is high to a certain extent, magnetizing current will actually occur only on the surface of the magnetic material in the absence of zero-sequence current. This magnetizing current cancels the magnetic flux density generated inside the magnetic body due to the free current, and is generated so that the magnetic flux density in that part becomes zero or a significantly small value (a magnetic field H is generated due to the free current inside the magnetic material).As a result, If the cylinder or cylinder has an annular magnetic material case shape and has an axially symmetrical shape or a shape that does not significantly deviate from the axially symmetrical shape without severe unevenness, the current to be detected with respect to the magnetic material The magnetic flux density in the space on the opposite side becomes significantly uniform.

For example, when the cylinder is an axisymmetric cylinder, the detected current whose algebraic sum is zero and the magnetic flux density generated by the magnetizing current on the inner surface of the cylinder cancel each other out, and the outer surface of the cylinder has a magnetic flux density on the inside. The magnetizing current is distributed according to the current to be detected so that the magnetizing current does not occur, and even if it does occur, the value is extremely small. In this way, when the algebraic sum of the currents is zero, for example, when the current to be detected is a three-phase load current and there is no zero-phase current, the magnetizing current on the outer surface of the cylinder becomes zero, and there is nothing in the space where the Rogowski coil exists. The magnetic flux density does not occur, or even if it does, its value is extremely small and does not change much in the longitudinal direction of the Rogowski coil.

Since the magnetic permeability of the space is sufficiently smaller than that of the magnetic material, the magnetic flux density remaining in the space where the Rogowski coil is located is sufficiently smaller than that inside the cylindrical magnetic material.The magnetic flux density remaining inside the magnetic material It is considered that the magnetic material is considerably non-uniform in the circumferential direction due to the reasons mentioned in the prior art section.

When the current has a zero-sequence component, the magnetizing current corresponding to the zero-sequence component of the current is distributed in the form of a closed circuit over the inner and outer surfaces of the cylinder. This magnetizing current produces a magnetic flux density within the magnetic material, but does not produce a magnetic flux density in the space outside it.Therefore, in the space where the Rogowski coil exists, there is virtually a magnetic flux density proportional to the zero-sequence current of the current to be detected. A magnetic flux density is generated. If the axial symmetry of the cylindrical body or the annular magnetic body case is somewhat distorted, there is a possibility that the magnetizing current related to the non-zero phase component of the current to be detected may also be partially distributed on the outer surface of the cylindrical body. However, the magnetic flux density and non-uniformity caused by this magnetizing current on the outside of the cylinder are significantly smaller than the magnetic flux density and non-uniformity generated at the same position by the same current component when there is no cylinder, and the Rogowski coil The residual voltage generated is also small.

By combining the magnetic material and the Rogowski coil as described above, a low-level zero-sequence current of about a few tenths of the three-phase load current is detected.

If the current to be detected is not a three-phase load current but, for example, a single-phase load current, even a minute load current can be detected without being affected by the unfavorable properties of the magnetic material.

Furthermore, by covering the outer periphery of the Rogowski coil with the magnetic case, the Rogowski coil is shielded by the magnetic case and is less affected by external disturbances.

Furthermore, placing the Rogowski coil in the center of the magnetic case minimizes the influence of external disturbances.

[First Embodiment] A first embodiment embodying the present invention will be described below with reference to the drawings.

As shown in FIGS. 1 and 2, a Rogowski coil 1 in a current detector is connected to a winding frame 2 made of a flexible non-magnetic material such as polystyrene curved into an annular shape. On the other hand, the solenoid is constituted by an annular solenoid 3 wound in an annular manner so that the number of turns n per unit length is constant and the average cross-sectional area S is constant along the axial direction of the winding frame 2. Note that it is desirable to increase the output voltage of the solenoid 3 by making the average cross-sectional area S as small as possible and increasing the number of turns n per unit length.

The lead wire 4a of the annular solenoid 3 is connected to the core wire of a coaxial cable 5 for measurement, and the lead wire 4b is connected to its outer conductor. The outer surface of the annular solenoid 3 is covered with an electrostatic shield 7, and the electrostatic shield 7 is connected to the outer conductor of the coaxial cable 5.

Note that if the annular solenoid 3 is wound only in one direction of the toroidal direction, for example, in the direction of the arrow A in FIG.
The induced voltage due to the magnetic flux interlinking with the axial center curve of the annular solenoid 3 is also added to the output of the annular solenoid 3, causing an error. In order to eliminate this, it is necessary to wind the annular solenoid 3 in an even number of layers, half of the layers in the direction of the arrow A, and the remaining half of the layers in the direction of the anti-A arrow. In the case of a single layer or an odd number of layers, as shown in Figure 3, unwinding [6 is provided,
It is configured to cancel the magnetic flux interlinking with the axial center curve.

The cylindrical body 8, which is loosely inserted concentrically with respect to the Rogowski coil 1, is formed into a cylindrical shape from a magnetic material such as soft iron, and the thickness of the cylindrical body 8 depends on the magnetic permeability of the magnetic material. It is set so that the magnetizing current is distributed virtually only on the surface of the cylindrical body 8. In this embodiment, the thickness is approximately 3 mm.

It is preferable that the axial length of the cylinder 8 is at least several times the cross-sectional diameter of the Rogowski coil 1, and the outer diameter of the cylinder 8 is slightly smaller than the diameter of the hollow part 9 formed by the Rogowski coil 1. When the axial length of the cylinder 8 is as described above, the Rogowski coil 1 is arranged not to be far away from the outer peripheral surface of the cylinder 8. Then, the wire to be measured is inserted through the insertion hole 10 provided at the axis of the cylindrical body 8, and the load current flowing through the wire to be measured is detected.

Incidentally, the winding frame 2 of the Rogowski coil 1 may be formed of a tough material.

As a first modification of the current detector of the first embodiment, as shown in FIG. The Rogowski coil 1 may be formed by connecting the windings of the double-ended Goski coil pieces 1a and lb in series and joining the winding frame 2 of the double-ended Goski coil pieces 1a and lb in an annular shape.

In addition, in the modified examples or examples described below, for convenience of explanation, the same reference numerals are given to the same or equivalent components as those explained in the above-mentioned first example or pond example,
The explanation will be omitted.

Further, as a second modification of the current detector 1, the windings of a pair of Rogowski coils 1 may be connected in series and closed to the cylinder body 8, as shown in FIG. In this way, it is possible to increase the output.

[Second example] Next, a second embodiment will be described with reference to FIG.

The cylindrical body 8 of the current detector 2 has an elliptical cross-sectional shape, and the Rogowski coil 1 also has a cylindrical body 8 corresponding to this cylindrical body 8.
Rogowski coil 1 is formed into an enlarged similar shape to cylinder #8.
It is located not far from the outer circumferential surface of the

FIG. 7 shows a second modification of the current detector of the second embodiment,
The cylinder body 8 and the Rogowski coil 1 are formed into a racetrack shape. In this second embodiment, the cross-sectional shape of the cylinder 8 is formed so that it does not deviate significantly from an axially symmetrical circular shape, and its surface is formed so that there are no sharp irregularities.

[Third Example] Next, a third embodiment will be described with reference to FIGS. 8 and 9.

In this embodiment, the cylindrical body 8 of the current detector 3 is formed of a magnetic material such as soft iron into an annular cylindrical case. That is, the cylindrical body 8 includes a first cylindrical member 8a having an inner circumferential wall of the cylindrical body 8 and an inverted-shaped vertical section, and a second cylindrical member 8a having an inverted curvature shape and an outer circumferential wall of the cylindrical body 8. 8b, and the two cylinder rod members 8a and 8b are removably connected to each other so as to form the storage space 11.
a.

The thickness of 8b is set to about 3 mm in this embodiment. A pair of Rogowski coils 1 electrically connected in series are housed in the storage space 11 in parallel. As shown in FIG. 8, this Rogowski coil 1 is arranged at the center of a storage space 11 formed by a cylinder 8.

A detected electric wire (not shown) is inserted into the insertion hole 10 of the cylindrical body 8.

FIG. 10 shows a first modification of the current detector of the third embodiment, in which the cylinder 8 is formed into an annular cylinder case whose planar shape is racetrack-shaped.

That is, the cylindrical body 8 has a racetrack-like planar shape and consists of a first cylindrical member 8a and a second cylindrical member 8b, both end surfaces of which are removably connected with magnetic material. The Rogowski coil 1 differs from the previous embodiment only in that its planar shape is formed in a racetrack shape similar to the cylinder 8 so that it is housed within the cylinder 8. Note that this planar shape is formed so that the cross-sectional shape of the cylinder 8 does not significantly deviate from the axially symmetrical circular shape, and the surface thereof is formed so that there are no sharp irregularities, as in the modification of the second embodiment. It is something to do.

Although not shown, the planar shape of the cylinder 8 and the Rogowski coil 1 may be oval as in the second embodiment.

FIG. 11 shows a third modification of the current detector of the third embodiment.

In this modification, the cylinder 8 is formed into an annular magnetic case with a circular cross section. That is, the cylindrical body 8 is constituted by first and second cylindrical body members 8a and 8b each having a circular cross section and a semicircular planar shape, and both cylindrical rod members 8a and 8b.
, 8b are integrally connected in an annular shape by joining flanges 12 provided at both ends of the flange 12 and tightening a nut 14 to a connecting bolt 13 inserted through the flange 12. The Rogowski coil 1 is stored in the storage space 11 of the cylinder 8. In this case as well, the Rogowski coil 1 is placed in the center of the storage space 11 formed by the cylinder 8, as shown in FIG.

Now, among the above embodiments, the current detector K1 of the second modification of the first embodiment and the third embodiment. Select option 3 and explain its effect.

FIG. 12 shows a simulated three-phase distribution line, and one end of the simulated distribution line is connected to a three-phase power supply E through a three-phase slider SD. The other end of the simulated three-phase distribution line is connected to a balanced Y-type load resistor R, and is also grounded from the load side neutral point N via a variable grounding resistor VR.

On the other hand, one phase on the secondary side of Sliduc SD is the switch SW.
A ground fault can be caused by the ground fault wire F via the ground fault wire F.

In addition, due to the current capacity of the circuit, each phase of the simulated three-phase distribution line is configured with a three-turn circuit to increase the maximum current value used.

A current detector Kl is applied to this simulated distribution line.

In 3, a simulated three-phase distribution line serving as a conductor of the current to be detected is passed through the insertion hole 10 of the cylindrical body 8, and the current detector is connected to the outside of the cylindrical body 8 of 1. A pair of Rogowski coils 1 are connected in series and arranged in the storage space 11 of the current detector 3.

The output of the three Rogowski coils 1 to each of the current detectors 1 and 3 is sent to the synchroscope S through an amplifier AP.
Connected to Y.

In this simulated three-phase distribution line, now open the switch SW,
The ground fault current Ir flowing through the ground fault wire F is set to zero. In this state, operate the Slider SD and the load current flowing through the resistor R■
change. At this time, the output generated in each current detector Kl and the three Rogowski coils I is the aforementioned residual voltage. The output amplified by the amplifier AP is read by the synchroscope SY, and the value is as shown in FIG.

As shown in Fig. 13, when the current detector is 3 (marked with *), the residual voltage is extremely small and does not depend on the load current l.This residual voltage r is due to electrostatic noise. Conceivable.

When the current detector is 1 (Δ mark), the residual voltage Vr is similarly small, but it tends to increase somewhat with the load current I. The thickness of the cylinder 8 is 2.5 at 1 for the current detector.
In the case of [mml (0 mark)] and the case of 2 [mml (x mark)], the residual voltage proportional to the load current increases as the thickness decreases.

This indicates that as the thickness of the cylinder 8 decreases, the magnetic shielding effect of the cylinder 8 on the magnetic flux density that generates a load current that does not include a zero-phase component weakens.

When this magnetic shielding effect is sufficient, the magnetizing current is distributed only in a portion that is considered to be virtually the surface with respect to the thickness of the cylindrical body 8. The description "j" means the magnetizing current distribution as described above.The thickness of the magnetic material at which it can be considered that the magnetizing current is virtually distributed over the surface is physically determined by the magnetic permeability of the magnetic material. In practice, it depends on the ratio between the load current and the minimum value of the zero-sequence current to be detected.Therefore, the thickness of the cylinder 8 is not limited to about 3 mil in the embodiment of the present application.

On the other hand, when the Rogowski coil 1 is used as a comparative example under the same conditions, the residual voltage Vr is extremely large and directly proportional to the load current I.

Next, when the switch SW is turned on and the resistance VR is changed, the output voltages of the Rogowski coils 1a of the current detectors Kl and 3 become as shown in FIG. That is, in the case of 1 in the current detector and in the case of 3 in the current detector, at worst, the ground fault current I.

From a small value of about 10 [mA], the output voltage V of Rogowski coil 1 is substantially proportional to the ground fault current It, and the ground fault current I, which is less than 1/2000 of the load current I, is accurately calculated. Detected. Although not shown in the graph, if the thickness of the cylinder 8 of 1 in the current detector is reduced to 2.5 [mmml, 2 [mmml], the minimum value of the ground fault current that can be practically detected becomes large. Become.

On the other hand, in the case of only the Rogowski coil 1 without the cylindrical body 8, the output V of the Rogowski coil 1 is a completely meaningless ground fault current l1, which is not proportional to the zero-sequence current due to the large residual voltage. value, and zero-sequence current cannot be detected.

Since the current detector Kl, 3 is equipped with the cylindrical body 8, when there is no zero-sequence current, the cylindrical body 8 (the first cylindrical body component 8a in the current detector 3, the same applies hereinafter) is covered. A magnetizing current is generated on the inner surface, which is the detection load current side, so that the load current I cancels the magnetic flux density generated on the outer side of the inner surface. The sum of this magnetizing current over the inner surface is equal to the algebraic sum of the load current I passing through the cylinder 8.

If the load current has a zero-sequence component, the magnetizing current
Distributed in the form of a closed circuit on the outer surface. This magnetizing current generates a magnetic flux density within the magnetic material of the cylinder 8, but does not generate a magnetic flux density outside the magnetic body.The magnetic flux density generated outside the a-body 8 is only due to the zero-sequence component of the load current. , the output of Rogowski coil 1 is proportional to this. When the load current I has no zero-phase component, the magnetizing current on the inner surface of the cylinder 8 is distributed so as to close at both end surfaces of the cylinder 8, and no magnetizing current is generated outside the cylinder 8. As a result, , if there is no zero-phase component, no output is generated in Rogowski coil 1.
If the circumferential direction component of the magnetic flux density is measured along the outer periphery of the cylinder 8 while maintaining the position [A], the result will be as shown in FIG. 15. In addition, V
p is the amplified output of the magnetic 10-band MP. Cylindrical body 8
When there is no cylinder 8, Vp is large and changes drastically in the circumferential direction, but when cylinder 8 is present, Vp is extremely small over the entire range of θ.This is because the existence of cylinder 8 is due to residual voltage. has been shown to be effective in removing

Although the cylindrical body 8 described above is formed in one piece, it can also be formed into two halves in the axial direction and formed into a single cylindrical body when assembled to the conductor of the current to be detected.

Furthermore, in an embodiment in which the cylinder body 8 is formed in a somewhat asymmetrical shape, there is a possibility that a magnetic flux density related to a non-zero phase component of the current to be detected may occur in the Rogowski coil 1, but even if it occurs, the magnitude will be and non-uniformity are small, and furthermore, according to the principle of the Rogowski coil 1, an output related to such magnetic flux density does not appear in the Rogowski coil 1, and it appears due to the expansion of the cross section of the Rogowski coil 1. This has the advantage that its value is small and only the zero-sequence current can be detected correctly.

Although each of the embodiments described above was intended to detect zero-sequence current, it can be understood that the present invention is also effective as a current detector for detecting not only zero-sequence current but also fault currents such as short circuits.

It is also possible to use a braided wire made of soft iron or the like as the magnetic case.

Note that the present invention is not limited to the above-mentioned embodiments, and can be arbitrarily modified without departing from the spirit of the present invention.

[Effects of the Invention] As described in detail above, the present invention provides a method in which a solenoid is connected to the outside of a cylindrical body formed of a magnetic material having a thickness such that the magnetizing current generated by the current to be detected is distributed virtually only on the surface. By detecting the detected current that passes through the inside of the cylinder with a Rogowski coil that is wound in a ring along the axial center curve so that the average cross-sectional area and the number of turns per unit length are constant. , in the space on the opposite side of the magnetic material from the current to be detected, a magnetic flux density that is proportional only to the zero-sequence component of the current to be detected occurs, so for example, when detecting a zero-sequence current, the output of the Rogowski coil as 1/2000 of the load current
It has the revolutionary advantage of being able to detect up to the following zero-sequence currents, and when detecting normal load currents, it is possible to detect minute load currents without worrying about the nonlinearity of the iron core, etc. can. Moreover, since the detection of the current to be detected is based on the well-known Ampere's circuit integral theorem and the magnetizing current in a physically clear magnetic material, it does not require any special know-how and is well-known in the field. This has the advantage that engineers can easily design and manufacture current detectors.

Furthermore, according to the current detection method of the present invention, the Rogowski coil can be separated from the cylindrical body even in the finished product stage, unlike the finished product ZCT in which the iron core and the secondary winding are inseparable. Each member can be divided into two parts along the direction of the conductor of the current to be detected. Therefore, it becomes easy to attach the current detector to the power distribution line, and it is also possible to measure the current detector at locations other than the distribution line, such as inside and outside of an air switch or a gas switch.

Furthermore, since the Rogowski coil is shielded by a magnetic case, the influence of external disturbances is reduced and the accuracy of the detected current can be improved.

Furthermore, since the Rogowski coil is placed in the center of the magnetic case, the influence of external disturbances is minimized, and the accuracy of the detected current can be improved.

[Brief Description of the Drawings] Figures 1 to 3 show a first embodiment, and Figure 1 is a partially cutaway front view of a zero-sequence current detector of the first embodiment embodying the present invention. , FIG. 2 is a side view, FIG. 3 is a plan view of the Rogowski coil, FIGS. 4 and 5 are modifications of the first embodiment, and FIG. 4 is a front view of the Rogowski coil piece. , FIG. 5 is a side view of the current detector, FIG. 6 is a plan view of the 'X current detector of the second embodiment, FIG. 7 is a front view of the current detector of a modification of the second embodiment, and FIG. 9 and 9 show the third embodiment, and FIG. 8 is a partially cutaway front view of the current detector.
FIG. 9 is an exploded partially cut-away front view of the case-shaped cylinder body, FIG. 10 is a modified example of the third embodiment, a partially cut-away front view of the current detector, and FIG. 11 is a partially cut-away front view of the third embodiment. 12 is an explanatory diagram showing a state in which a current detector is attached to a simulated three-phase distribution line for detecting zero-phase current; FIG. is a graph showing the relationship between load current and residual voltage, FIG. 14 is a graph showing the relationship between ground fault current and Rogowski coil output, and FIG.
15(b) is a graph showing the distribution of magnetic flux density outside the cylinder of the first example. DESCRIPTION OF SYMBOLS 1... Rogowski coil, 2... Winding frame, 3... Annular solenoid, 8... Cylindrical body. Patent applicant Energy Support Co., Ltd. Agent Patent attorney On 1) Hironobu (and 1 other person) Figure 18 Figure 14 Figure 15 (b) Page 15 (Q)

Claims (1)

[Claims] 1. A solenoid is placed on the outside of a cylindrical body made of a magnetic material having a thickness such that the magnetizing current generated by the current to be detected is distributed only on the surface thereof, along the axial center curve of the cylindrical body. A current detection method characterized by detecting a detected current passing through the inside of a cylinder of a Rogowski coil which is wound in an annular manner so that the average cross-sectional area and the number of turns per unit length are constant. 2. In a current detector in which a Rogowski coil formed by winding a coil around a core material is made into a circular shape and a conductor through which the current to be measured passes through the inside of the Rogowski coil is passed through, the outer periphery of the Rogowski coil is surrounded by a magnetic material case. A current detector characterized by being covered with. 3. The current detector according to claim 2, wherein the Rogowski coil is arranged at the center of a magnetic case.