JP7633838B2 - Current Sensors - Google Patents

Description

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

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, damage, or deterioration in order to protect against electric shock, protect against fire, and improve maintainability in photovoltaic power generation facilities.

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 circuit back and forth through the coil, applying an AC voltage to the wound coil, and detecting the second harmonic generated by magnetic saturation of the core due to leakage current.

Patent Document 2 also describes a configuration of a current sensor element that detects a current including a DC component, comprising a main sensor, an auxiliary sensor, and a permanent magnet that applies a bias magnetic field to the magnetic core of the main sensor and the magnetic core of the auxiliary sensor, the main sensor comprising an annular first magnetic core, 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 a magnetic material is provided that surrounds the main sensor, the permanent magnet, and the auxiliary sensor.

JP 2013-110925 A JP 2020-143962 A

In the sensor described in Patent Document 1 or Patent Document 2, a coil is wound around a ring-shaped magnetic core and excited with alternating current, so that a zero-phase voltage is induced in the electric circuit to be detected for leakage current by the excitation. 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 amounts of power, but this results in a larger capacitance to the ground than general electrical equipment.

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, and there is a problem that the leakage current in the event of a fault is small and difficult to detect.

The object of the present invention is to provide a current sensor that enables stable and highly sensitive current detection, regardless of the ground capacitance of the solar power generation system.

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 second annular 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.

The present invention makes it possible to obtain a current sensor that can achieve stable and highly sensitive current detection without being affected by the ground capacitance of the solar power generation system.

FIG. 2 is a connection diagram of the current sensor according to the first embodiment. FIG. 11 is a connection diagram of a current sensor as a comparative example.

Before describing the embodiments of the present invention, we will explain a current sensor as a comparative example that uses a ring-shaped magnetic body to detect DC leakage current.

Figure 2 is a connection diagram of a current sensor as a comparative example. The current sensor as a comparative example has a structure in which a pair of main circuit conductors 12 are inserted into a core 11 made of a soft magnetic material for both directions.

An excitation winding 13 and a detection winding 14 are wound around the core 11, and an excitation circuit 15 is connected to the excitation winding 13, and a secondary harmonic detection circuit 16 is connected to the detection winding 14. If 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, but if 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 difference in currents is induced in the core 11.

At this time, the 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 a bias occurs in the magnetic characteristics due to the magnetic field caused by the leakage current induced inside the core 11, and a second harmonic is induced in the detection winding 14. This second harmonic is detected by the second harmonic detection circuit 16 to detect the presence or absence of leakage current.

Figure 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 in the current sensor of the comparative example will be omitted. The current sensor of this embodiment is a current sensor that detects 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 a ring-shaped first magnetic core 21 through which the 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 a ring-shaped second magnetic core 22 through which the 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 with a resistor 29, and both ends of the resistor 29 are connected to the second harmonic detection circuit 2a.

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 with the same number of turns. The first excitation winding 24 and the second excitation winding 25 are connected in series with opposite polarity and excited by an excitation circuit 26 so that voltages of opposite polarity 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 polarity.

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 the voltage induced by the excitation current, and are connected to a current detection resistor 29. In the current sensor of this embodiment, the voltage drop of the current detection resistor 29 is input to the second harmonic detection circuit 2a, and the leakage current is detected by detecting the second harmonic.

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, allowing for highly sensitive leakage current detection.

In addition to eliminating the effects of the loop impedance described above, the current sensor of this embodiment can cancel out the noise current caused by the switching of the power semiconductor element and flowing through the capacitance to ground by connecting two detection windings in inverse parallel, improving the signal-to-noise ratio of the sensor and enabling leakage current detection with high sensitivity.

In addition, the second harmonic generated from the winding on the detection side has a larger current component than the voltage component. Therefore, detecting the current rather than the voltage allows for more efficient and sensitive detection of the second harmonic. 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 high sensitivity.

In the above embodiment, the main circuit conductors 23 are described as a pair of two conductors for a round trip, but they may be a single conductor or three or more conductors.

In the above embodiment, a current sensor applied to a DC circuit of a photovoltaic power generation facility was described as an example. The main circuit conductor 23 is not limited to being connected to a photovoltaic power generation facility, and this embodiment can also be applied when connected to other facilities.

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 (3)

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

Images