Current Sensors

Abstract

To provide a current sensor that does not depend on a ground electrostatic capacitance of a photovoltaic power generation system and is stable and has high sensitivity.SOLUTION: A current sensor detecting a direct current flowing in a main circuit conductor comprises a first sensor assembly and a second sensor assembly, the first sensor assembly comprises a first annular magnetic core through which the main circuit conductor penetrates, and a first excitation coil and a first detection coil that are wound around the first magnetic core, the second sensor assembly comprises a second annular magnetic core through which the main circuit conductor penetrate, and a second excitation coil and a second detection coil that are wound around the second magnetic core, a number of turns of the first excitation coil is the same as that of the excitation coil, the first excitation coil is connected with the second excitation coil at the reversed polarity as well as being connected to an excitation circuit, the first detection coil and the second detection coil are connected to a resistor in series, and both ends of the resistor are connected to a secondary higher harmonic detection circuit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a current sensor for detecting leakage current in DC electrical equipment. [Background technology]

[0002] As mega solar and other photovoltaic power generation facilities become more widespread, it is necessary to detect leakage current caused by human contact with electrical circuits and damage or deterioration in order to protect against electric shock, protect against fire and improve maintainability in photovoltaic power generation facilities.

[0003] To address these issues, Patent Document 1 describes a technology for detecting leakage current by winding a coil around a ring-shaped magnetic core, passing a DC current circuit back and forth through it, applying an AC voltage to the wound coil, and detecting the second harmonic generated by magnetic saturation of the core due to leakage current.

[0004] Furthermore, Patent Document 2 describes a configuration of "a current sensor element for detecting a current including a DC component, comprising a main sensor, an auxiliary sensor, and a permanent magnet for applying a bias magnetic field to a magnetic core of the main sensor and the magnetic core of the auxiliary sensor, the main sensor comprising an annular first magnetic core, and a detection winding and an excitation winding wound around the first magnetic core, the auxiliary sensor comprising an annular second magnetic core, and a compensation winding wound around the second magnetic core, the main sensor and the auxiliary sensor are stacked with the permanent magnet interposed therebetween, and a case made of magnetic material is provided surrounding the main sensor, the permanent magnet, and the auxiliary sensor." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-110925 A [Patent Document 2] JP 2020-143962 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the sensor in Patent Document 1 or Patent Document 2, a coil is wound around a ring-shaped magnetic core and excited with AC, so that a zero-phase voltage is induced by the excitation in the electric circuit to be detected for leakage current. On the other hand, in a solar power generation facility, solar modules are deployed over a wide area, such as on the ground or rooftop, to obtain large electric power, but this results in a larger capacitance to the ground than general electrical facilities.

[0007] When the sensor in Patent Document 1 or Patent Document 2 is applied to a circuit with such a large capacitance to the ground, the zero-phase voltage induced by the excitation of the sensor causes a current to flow in a loop via the capacitance to the ground and the grounding electrode, hindering the operation of the sensor. In addition, the DC circuits of photovoltaic power generation facilities are often grounded with high resistance, which causes a problem that the leakage current during a fault is small and difficult to detect.

[0008] An object of the present invention is to provide a current sensor that is not affected by the capacitance to ground of a solar power generation system and that enables stable and highly sensitive current detection. [Means for solving the problem]

[0009] A preferred example of the present invention is a current sensor for detecting a direct current flowing through a main circuit conductor, comprising: A first sensor unit and a second sensor unit are provided, The first sensor unit 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 second sensor unit includes: a ring-shaped second magnetic core through which the main circuit conductor passes, and a second excitation winding and a second detection winding wound around the second magnetic core, The first excitation winding and the second excitation winding have the same number of turns, the first excitation winding and the second excitation winding are connected with opposite polarity and connected to an excitation circuit, the first detection winding and the second detection winding are connected in series with a resistor, and both ends of the resistor are connected to a second harmonic detection circuit. Effect of the Invention

[0010] According to the present invention, it is possible to obtain a current sensor that realizes stable and highly sensitive current detection without being affected by the capacitance to ground of a solar power generation system. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a connection diagram of the current sensor according to the first embodiment. [Diagram 2] FIG. 11 is a connection diagram of a current sensor as a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Prior to describing the embodiments of the present invention, a current sensor using a ring-shaped magnetic body for detecting a DC leakage current will be described as a comparative example.

[0013] 2 is a connection diagram of a current sensor as a comparative example. The current sensor as the comparative example has a structure in which a pair of main circuit conductors 12 extend back and forth through a core 11 made of a soft magnetic material.

[0014] An excitation winding 13 and a detection winding 14 are wound around the 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. When there is no abnormality in the load connected to the main circuit and no leakage current flows, the currents flowing in the main circuit conductors 12 are equal and in opposite directions. However, when a ground fault occurs in the load and a leakage current flows, causing a difference in the currents flowing in the opposite directions in the main circuit conductors 12, a magnetic field corresponding to the current difference is induced in the core 11.

[0015] At this time, core 11 is excited by excitation circuit 15 and excitation winding 13, and a voltage corresponding to the excitation current is induced in detection winding 14, but a bias occurs in the magnetic characteristics due to the magnetic field caused by the leakage current induced inside core 11, and a second harmonic is induced in detection winding 14. This second harmonic is detected by second harmonic detection circuit 16 to detect the presence or absence of leakage current. EXAMPLES

[0016] FIG. 1 is a connection diagram of a current sensor according to a first embodiment of the present invention. Explanation of the same matters as those of the current sensor according to the comparative example will be omitted. The current sensor according to this embodiment is a current sensor for detecting a direct current flowing through a main circuit conductor, and includes a first sensor unit and a second sensor unit. The first sensor unit includes an annular first magnetic core 21 through which a main circuit conductor 23 passes, and a first excitation winding 24 and a first detection winding 27 wound around the first magnetic core 21. The second sensor unit includes an annular second magnetic core 22 through which a main circuit conductor passes, and a second excitation winding 25 and a second detection winding 28 wound around the second magnetic core 22. The first excitation winding 24 and the second excitation winding 25 are connected with opposite polarities and are connected to an excitation circuit 26. The first detection winding 27 and the second detection winding 28 are connected in series to a resistor 29, and both ends of the resistor 29 are connected to the second harmonic detection circuit 2a.

[0017] The first magnetic core 21 and the second magnetic core 22 are made of a soft magnetic material. The first magnetic core 21 and the second magnetic core 22 are provided with a first excitation winding 24 and a second excitation winding 25 having the same number of turns. The first excitation winding 24 and the second excitation winding 25 are connected in series with opposite polarities and excited by an excitation circuit 26 so that voltages of opposite polarities are generated in the first excitation winding 24 and the second excitation winding 25. The first excitation winding 24 and the second excitation winding 25 may be connected in parallel with opposite polarities.

[0018] A first detection winding 27 and a second detection winding 28 are wound around the first magnetic core 21 and the second magnetic core 22, respectively. The first detection winding 27 and the second detection winding 28 are connected in series with a polarity that cancels out the voltage induced by the excitation current, and are connected to a current detection resistor 29. The current sensor of this embodiment is configured to input the voltage drop of the current detection resistor 29 to the second harmonic detection circuit 2a, and detect the leakage current by detecting the second harmonic.

[0019] The current sensor of this embodiment uses two annular magnetic cores, and by exciting each core in opposite phase, it cancels out the zero-phase voltage induced in the electric circuit to be detected for leakage current, and is not affected by the capacitance to earth and the loop impedance via the ground electrode. In addition, the detection windings wound around the two cores are connected in series with a polarity that cancels out the induced voltage due to the excitation current, and a current detection resistor is inserted in this series circuit to detect the current flowing through the detection winding, thereby enabling leakage current detection with high sensitivity.

[0020] According to the current sensor of this embodiment, in addition to the effect of eliminating the influence of the loop impedance described above, the noise current caused by the switching of the power semiconductor element and flowing through the ground capacitance is short-circuited and canceled by connecting the two detection windings in inverse parallel, thereby improving the signal-to-noise ratio of the sensor and making it possible to detect leakage currents with high sensitivity.

[0021] In addition, the second harmonic generated from the winding on the detection side has a larger current component than a voltage component. Therefore, detecting the current rather than the voltage allows the second harmonic to be detected more efficiently and with higher sensitivity. According to this embodiment, the first detection winding 27 and the second detection winding 28 are connected in series and a resistor is inserted, so that the current including the second harmonic flowing through the first detection winding 27 and the second detection winding 28 can be detected efficiently and with higher sensitivity.

[0022] In the above embodiment, the main circuit conductor 23 is described as a pair of two conductors for a round trip, but it may be a single conductor or three or more conductors.

[0023] In the above embodiment, the current sensor is applied to the DC circuit of the photovoltaic power generation facility. The present embodiment can be applied not only to the case where the main circuit conductor 23 is connected to the photovoltaic power generation facility, but also to the case where the main circuit conductor 23 is connected to other facilities. [Explanation of symbols]

[0024] Reference Signs List 11...core, 12...main circuit conductor, 13...excitation winding, 14...detection winding, 15...excitation circuit, 16...second harmonic detection circuit, 21...first magnetic core, 22...second magnetic core, 23...main circuit conductor, 24...first excitation winding, 25...second excitation winding, 26...excitation circuit, 27...first detection winding, 28...second detection winding, 29...current detection resistor, 2a...second harmonic detection circuit

Claims

1. A current sensor for detecting a direct current flowing through a main circuit conductor, A first sensor unit and a second sensor unit are provided, The first sensor unit includes: a first magnetic core having an annular shape and through which the main circuit conductor passes; a first excitation winding and a first detection winding wound around the first magnetic core; The second sensor unit includes: a second annular magnetic core through which the main circuit conductor passes; a second excitation winding and a second detection winding wound around the second magnetic core; The first excitation winding and the second excitation winding have the same number of turns, the first excitation winding and the second excitation winding are connected with opposite polarities and are connected to an excitation circuit, the first detection winding and the second detection winding are connected in series with a single resistor, and both ends of the resistor are connected to a second harmonic detection circuit; The first excitation winding and the second excitation winding are connected in parallel to each other.

2. 2. The current sensor according to claim 1, The main circuit conductor is A current sensor consisting of a reciprocating pair.

3. 3. The current sensor according to claim 1, The main circuit conductor is A current sensor connected to a solar power generation facility.

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