JP7444706B2 - current sensor - Google Patents

Description

The present invention relates to a current sensor that detects leakage current in DC electrical equipment.

With the spread of solar power generation equipment such as mega solar, it is necessary to detect the occurrence of leakage current due to human contact with electrical circuits, damage, and deterioration in order to protect against electric shock, protect against fire, and improve maintainability of solar power generation equipment.

To solve this problem, Patent Document 1 discloses that a coil is wound around an annular magnetic core, a DC current path is passed through the magnetic core in a reciprocating manner, and an AC excitation voltage is applied to the wound coil to prevent leakage. A method is described in which leakage current is detected by detecting second harmonics generated by magnetic saturation of the core due to current.

Japanese Patent Application Publication No. 2013-110925

In the conventional sensor, a coil is wound around an annular magnetic core and is excited with alternating current, so that a zero-sequence voltage is induced in the electrical path to be detected for leakage due to the excitation. On the other hand, solar power generation equipment attempts to obtain large amounts of power by deploying solar modules over a large area, such as on the ground or on a rooftop, but this results in a larger ground capacitance than general electrical equipment. . When a conventional sensor is applied to a circuit with such a large ground capacitance, the zero-sequence voltage induced by excitation of the sensor causes a current to flow in the loop via the ground capacitance and the ground electrode, and the sensor There was a problem that the operation of the device was hindered.

An object of the present invention is to provide a stable current detection means that is not affected by the ground capacitance of a solar power generation system or the like.

In order to solve the above-mentioned problems, the current sensor of the present invention uses two annular magnetic cores and excites each core in opposite phases to reduce the zero-sequence voltage induced in the electrical circuit to be detected for earth leakage. This cancels out the effects of ground capacitance and loop impedance via the ground electrode.

To give an example of the "current sensor" of the present invention,
A current sensor that detects a direct current flowing through a main circuit conductor,
Equipped with a main sensor and an auxiliary sensor,
The main sensor includes a first annular magnetic core through which the main circuit conductor passes, and a first excitation winding and a first detection winding wound around the first magnetic core,
The auxiliary sensor includes a second annular magnetic core through which a main circuit conductor passes, and a second excitation winding that is wound around the second magnetic core and has the same number of turns as the first excitation winding . a second detection winding wound around the second magnetic core ;
The first excitation winding and the second excitation winding are connected in series or parallel to an excitation circuit so as to excite their respective magnetic cores in opposite phases ;
The first detection winding and the second detection winding are connected in parallel to cancel noise and are connected to a second harmonic detection circuit .

According to the present invention, it is possible to provide a stable current detection means that is not affected by the ground capacitance of a solar power generation system or the like.

Problems, configurations, and effects other than those described above will be made clear by the description of the embodiments below.

It is a connection diagram of the current sensor of Example 1 in this invention. It is a connection diagram of the current sensor of Example 2 in this invention. It is a structural diagram of the current sensor of Example 3 in this invention. FIG. 2 is a connection diagram of a current sensor according to the prior art.

Prior to describing embodiments of the present invention, a conventional technique for detecting DC leakage current using an annular magnetic body will be described.

FIG. 4 is a connection diagram of a current sensor in the prior art. A current sensor according to the conventional technology has a structure in which a pair of main circuit conductors 12 for reciprocation pass through an annular magnetic core 11 made of a soft magnetic material. An excitation winding 13 and a detection winding 14 are wound around the annular magnetic core 11, an excitation circuit 15 is connected to the excitation winding 13, and a second harmonic detection circuit 16 is connected to the detection winding 14. Ru. An alternating current excitation voltage is applied to the excitation winding 13 from an excitation circuit 15 . If there is no abnormality in the load connected to the main circuit and no leakage current is flowing, the currents flowing in the main circuit conductor 12 are equal and opposite to each other, but if a ground fault occurs in the load, leakage current When a difference occurs in the current flowing in the opposite direction to the main circuit conductor 12 due to the flow of the current, a magnetic field corresponding to the difference in current is induced in the magnetic core 11. At this time, the magnetic core 11 is excited by the excitation circuit 15 and the excitation winding 13, and a voltage corresponding to the excitation current is induced in the detection winding 14, but leakage induced inside the magnetic core 11 occurs. The magnetic field based on the current causes a bias in the magnetic properties of the magnetic core made of a soft magnetic material, and a second harmonic is induced in the detection winding 14. This second harmonic is detected by a second harmonic detection circuit 16 to detect the presence or absence of leakage current.

In order to obtain large amounts of power, solar power generation equipment deploys solar modules over a wide area, which results in it having a larger ground capacitance than general electrical equipment. When a conventional current sensor is used in a circuit with such a large ground capacitance, the zero-sequence voltage induced by excitation of the current sensor causes a current to flow through the loop via the ground capacitance and the ground electrode. , a problem arises in that the operation of the current sensor is inhibited.

The present invention solves this problem and provides a stable current sensor that is not affected by ground capacitance.

FIG. 1 shows a connection diagram of a current sensor according to a first embodiment of the present invention. The current sensor of this embodiment includes a main sensor 200 and an auxiliary sensor 210. The main sensor 200, like the conventional current sensor, includes a first annular magnetic core 21 made of a soft magnetic material, a pair of main circuit conductors 22 for reciprocation, and a first excitation coil wound around the first magnetic core. The structure includes a winding 23, a first detection winding 24, an excitation circuit 25 connected to the first excitation winding, and a second harmonic detection circuit 26 connected to the first detection winding, and its operating principle is as follows. The same is true. The auxiliary sensor 210 has an annular second magnetic core 27 similar to the first magnetic core, and the second magnetic core has a second excitation winding 28 having the same number of turns as the first excitation winding 23. is wound. The first excitation winding 23 and the second excitation winding 28 are connected in series with opposite polarities and connected to the excitation circuit 25 . Here, "connected in series with mutually opposite polarities" means that the lines of magnetic force generated in the first magnetic core 21 by the first excitation winding 23 and the lines of magnetic force generated in the second magnetic core 27 by the second excitation winding 28 Connecting in series so that the lines of magnetic force generated in the magnetic field are in the opposite direction (opposite phase). The main circuit conductor 22 is arranged to penetrate the first magnetic core 21 and the second magnetic core 27.

When the current sensor of this embodiment is used in a DC circuit of a solar power generation facility, the voltages induced in the main circuit conductor 22 by excitation of the current sensor have opposite phases in the main sensor and the auxiliary sensor, and cancel each other out. Therefore, no zero-sequence voltage is generated, and it is no longer affected by ground capacitance and loop impedance via the ground electrode.

In addition, in FIG. 1, the first excitation winding 23 and the second excitation winding 28 are connected in series with mutually opposite polarities for excitation, but the first excitation winding 23 and the second excitation winding A similar effect can also be obtained by connecting the magnets 28 in parallel with opposite polarities and energizing them.

FIG. 2 shows a connection diagram of a current sensor according to a second embodiment of the present invention. Components that are the same as those in Example 1 are given the same reference numerals and descriptions thereof will be omitted.

This embodiment has a structure in which the first magnetic core 21 of the main sensor 200 and the second magnetic core 27 of the supplementary sensor 210 are provided, and the main circuit conductor 22 penetrates them, as in the first embodiment. be. Each core is provided with a first excitation winding 23 and a second excitation winding 28 having the same number of turns, connected in series with opposite polarities, and excited by an excitation circuit 25. Note that this connection may be in antiparallel.

In this embodiment, the first detection winding 24 is wound around the first magnetic core 21 of the main sensor 200, and the second detection winding 29 is wound around the second magnetic core 27 of the auxiliary sensor 210. These are connected in antiparallel and input to the second harmonic detection circuit 26. Here, "connecting them in antiparallel" means that the first detection winding 24 and the second detection winding 29 are connected in parallel so as to cancel out noise. Then, leakage current is detected by detecting the second harmonic.

According to this embodiment, in addition to the effect of eliminating the influence of the ground capacitance and the loop impedance via the ground electrode of the first embodiment, the The noise current flowing through the capacitance can be canceled by short-circuiting the two detection windings by connecting them in antiparallel, thereby improving the S/N ratio of the current sensor.

FIG. 3 shows a structural diagram of a current sensor according to Example 3 of the present invention. 3(a) is a plan view seen from above, and FIG. 3(b) is a sectional view taken along line AA in FIG. 3(a). The current sensor of this example is a specific example of the current sensor of Example 2. The current sensor includes a cylindrical case 30, and has a cylindrical hole 31 in the center thereof through which the main circuit conductor passes.

As shown in the cross-sectional view of FIG. 3(b), the current sensor has a structure in which a main sensor 300 and an auxiliary sensor 310 are stacked with a permanent magnet 38 interposed therebetween. The main sensor 300 is configured by winding a first excitation winding 33 and a first detection winding 34 around a first annular magnetic core 32 . The auxiliary sensor 310 is constructed by winding a second excitation winding 36 and a second detection winding 37 around a second annular magnetic core 35 that is similar to the first magnetic core 32 . For the first magnetic core 32 and the second magnetic core 35, a soft magnetic material such as ferrite or NiFe alloy (permalloy) is used. The stacked auxiliary sensor 310, permanent magnet 38, and main sensor 300 are housed as one body in a case 30 made of magnetic material. The case 30 is arranged above the first magnetic core 32 of the main sensor, on the sides of the first magnetic core 32 of the main sensor and the second magnetic core 35 of the auxiliary sensor, and below the second magnetic core 35 of the auxiliary sensor. It also extends inside the hole 31 to a position that covers the inner peripheries of the first magnetic core 32 and the second magnetic core 35 . The permanent magnet 38 inserted between the first magnetic core 32 and the second magnetic core 35 is an annular magnet, and is directed from the second magnetic core 35 to the first magnetic core 32 in the vertical direction of the figure. It is magnetized. The magnetic flux emitted from the permanent magnet flows toward the case 30 made of a magnetic material inside the hole 31, as shown by the arrow in the figure. As a result, by applying a bias magnetic field perpendicular to the circumferential direction to the annular first magnetic core 32 and second magnetic core 35, the coercive force of the magnetic cores is kept low and the sensor operating point due to large ground fault current is reduced. Prevent change.

The first excitation winding 33 of the main sensor and the second excitation winding 36 of the auxiliary sensor may be connected in series or parallel with opposite polarity within the sensor, or their respective terminals may be connected outside the sensor. They may be connected in series or in parallel with opposite polarity using wiring outside the sensor. Further, the first detection winding 34 of the main sensor and the second detection winding 37 of the auxiliary sensor may be connected in antiparallel within the sensor, or their respective terminals may be brought out outside the element. You can also connect them in antiparallel using external wiring.

In this embodiment, the case 30 is made of a magnetic material so that it also serves as a magnetic circuit yoke through which magnetic flux passes, but the case 30 may be made of a non-magnetic material.

According to the current sensor of this embodiment, since the main sensor and the auxiliary sensor are stacked and housed in one case, the current sensor of the present invention can be miniaturized as one element. In addition, by creating a stacked structure of the main sensor and auxiliary sensor with a permanent magnet interposed between them for applying a bias magnetic field, it is possible to apply a bias magnetic field to two magnetic cores with a single permanent magnet, reducing costs. Therefore, it is possible to provide a current sensor element that is reduced in size and that increases in size.

In this example, a sensor that embodies the current sensor of Example 2 has been described, but the current sensor of Example 1 can be obtained by removing the second detection winding.

DESCRIPTION OF SYMBOLS 11... Magnetic core, 12... Main circuit conductor, 13... Excitation winding, 14... Detection winding, 15... Excitation circuit, 16... Secondary harmonic detection circuit,
DESCRIPTION OF SYMBOLS 21... First magnetic core, 22... Main circuit conductor, 23... First excitation winding, 24... First detection winding, 25... Excitation circuit, 26... Second harmonic detection circuit, 27... Second magnetic core, 28... second excitation winding, 29... second detection winding,
30... Case, 31... Hole, 32... First magnetic core, 33... First excitation winding, 34... First detection winding, 35... Second magnetic core, 36... Second excitation winding , 37... second detection winding,
200...Main sensor, 210...Auxiliary sensor, 300...Main sensor, 310...Auxiliary sensor.

Claims (4)

A current sensor that detects a direct current flowing through a main circuit conductor,
Equipped with a main sensor and an auxiliary sensor,
The main sensor includes a first annular magnetic core through which the main circuit conductor passes, and a first excitation winding and a first detection winding wound around the first magnetic core,
The auxiliary sensor includes a second annular magnetic core through which a main circuit conductor passes, and a second excitation winding that is wound around the second magnetic core and has the same number of turns as the first excitation winding . a second detection winding wound around the second magnetic core ;
The first excitation winding and the second excitation winding are connected in series or parallel to an excitation circuit so as to excite their respective magnetic cores in opposite phases ;
A current sensor characterized in that the first detection winding and the second detection winding are connected in parallel to cancel noise and are connected to a second harmonic detection circuit . A current sensor that detects a direct current flowing through a main circuit conductor,
Equipped with a main sensor and an auxiliary sensor,
The main sensor includes a first annular magnetic core through which the main circuit conductor passes, and a first excitation winding and a first detection winding wound around the first magnetic core,
The auxiliary sensor includes a second annular magnetic core through which a main circuit conductor passes, and a second excitation winding that is wound around the second magnetic core and has the same number of turns as the first excitation winding. Prepare,
The first excitation winding and the second excitation winding are connected in series or parallel to an excitation circuit so as to excite their respective magnetic cores in opposite phases;
the first detection winding is connected to a second harmonic detection circuit;
A current sensor characterized in that the main sensor and the auxiliary sensor are stacked on top of each other with a permanent magnet for bias interposed therebetween and housed in a case. The current sensor according to claim 2 ,
A current sensor comprising a case made of a magnetic material surrounding the main sensor, the permanent magnet, and the auxiliary sensor. The current sensor according to claim 3 ,
The current sensor is characterized in that the permanent magnet applies a bias magnetic field perpendicular to the circumferential direction to the annular first magnetic core and the second magnetic core.

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