JP2020197396A - Current detection device - Google Patents

Abstract

To detect abnormality in a current transformer by a simple configuration.SOLUTION: A current detection device includes: a current transformer mounted on a wire to which load can be electrically connected and disconnected; a measurement circuit which is connected between terminals of a coil of the current transformer and has a voltage dividing resistor connected in parallel with the coil with respect to a voltage source; a switch which is connected in series with the voltage dividing resistor and connected in parallel with the coil with respect to the voltage source; and a control device which performs a current detection operation for detecting a current flowing through the wire based on a measurement value measured by the measurement circuit while the switch is on, and performs an abnormality determination operation for determining the presence/absence of disconnection of the current transformer based on a measurement value measured by the measurement circuit while the switch is off.SELECTED DRAWING: Figure 3

Description

The present invention relates to a current detection device that detects a current flowing through an electric wire to which a load can be connected and disconnected.

Conventionally, the first current sensor and the second electric wire (V phase) connected to the interconnection point of the first electric wire (U phase) of the distributed power generation device connected to the single-phase three-wire power system. It has been proposed to detect an abnormality (disconnection, etc.) of each of the second current sensors connected to the interconnection point of the above (see, for example, Patent Document 1). The distributed power generation device includes a first relay capable of connecting and disconnecting the power load and the power load between the first electric wire (U phase) and the third electric wire (N phase), and a second relay. It is provided with a second relay capable of connecting and disconnecting a power load between the electric wire (V phase) and the third electric wire (N phase). The control means of the distributed power generation device acquires the current value detected by the first current sensor immediately before and immediately after connecting the power load between the first electric wire and the third electric wire by the first relay. , It is determined that the first current sensor has failed when the amount of change in the acquired current value is within a predetermined range. Further, the current value detected by the second current sensor is acquired immediately before and immediately after the power load is connected between the second electric wire and the third electric wire by the second relay, and the change of the acquired current value is obtained. When the amount is within the predetermined range, it is determined that the second current sensor has failed.

Japanese Unexamined Patent Publication No. 2011-160562

However, the determination method described in Patent Document 1 may not be able to appropriately determine an abnormality such as a disconnection of a current transformer (CT) attached to an electric wire. For example, in a distributed power supply system in which one of the first and second electric wires (U phase and V phase) (for example, U phase) and the third electric wire (N phase) are connected, the distributed type is used. Since it is usually not possible to connect the internal load of the power supply system to the other wire (for example, V phase) of the first and second wires, the current transformer attached to the other wire may be abnormal. Cannot be determined.

By the way, if it is measured by the measuring circuit connected to the winding of the current transformer that no current is flowing through the electric wire to which the current transformer is attached, it may be determined that the winding is broken. Be done. However, even when the external load is not connected to the electric wire to which the current transformer is attached, no current flows through the electric wire, so that the external load is connected to the electric wire as in the above-mentioned distributed power generation system. In a system that cannot recognize whether or not the current transformer is installed, it is not possible to distinguish whether the current transformer winding is broken or an external load is not connected, and there is a risk of erroneously determining an abnormality. ..

An object of the current detection device of the present invention is to provide a current detection device capable of appropriately detecting an abnormality of a current transformer with a simple configuration.

The current detector of the present invention has adopted the following means in order to achieve the above-mentioned main object.

The current detector of the present invention
A current detector that detects the current flowing through an electric wire whose load can be electrically connected and disconnected.
The current transformer attached to the electric wire and
A measuring circuit having a voltage dividing resistor connected between the terminals of the winding of the current transformer and connected in parallel with the winding with respect to the voltage source.
A switch connected in series with the voltage dividing resistor to the voltage source and connected in parallel with the winding.
A current detection operation for detecting the current flowing through the electric wire based on the measured value measured by the measuring circuit with the switch turned on is performed, and the measurement measured by the measuring circuit with the switch turned off. A control device that performs an abnormality determination operation to determine the presence or absence of disconnection of the current transformer based on the value, and
The gist is to prepare.

In the current detection device of the present invention, a current transformer attached to an electric wire and a voltage dividing resistor connected between the terminals of the current transformer winding and connected in parallel with the current transformer winding to the voltage source. In addition to the measurement circuit having the above, a switch connected in series with the voltage dividing resistor and connected in parallel with the winding is provided for the voltage source. Then, the current detection operation for detecting the current flowing through the electric wire is performed based on the measured value measured by the measuring circuit with the switch turned on, and based on the measured value measured by the measuring circuit with the switch turned off. The abnormality determination operation for determining the presence or absence of disconnection of the current transformer is performed. When the switch is turned off, if the winding of the current transformer is not broken, the winding is connected to the voltage source and the voltage dividing resistor is disconnected, and the winding of the current transformer is broken. When is occurring, both the winding and the voltage dividing resistor are disconnected from the voltage source, so it acts on the winding terminals depending on whether the winding is broken or not. It is possible to cause a large change in the potential. Therefore, the presence or absence of disconnection of the winding can be determined by measuring the voltage acting between the terminals by the measuring circuit connected between the terminals of the winding of the current transformer. Moreover, since it is only necessary to provide a switch, the configuration required for determining the presence or absence of disconnection of the winding can be made simpler. Since the combined impedance between the terminals of the current transformer changes depending on whether the winding of the current transformer has a disconnection or not, the combined impedance between the terminals of the current transformer changes. It is also conceivable to determine the presence or absence of disconnection of the winding by measuring the voltage change that occurs in response with the measurement circuit. However, since the resistance value of the winding is generally much larger than the resistance value of the voltage dividing resistor, the degree of change in the combined impedance is small, and the presence or absence of disconnection is determined by the measured value measured by the measurement circuit. It is difficult to judge.

In such a current detection device of the present invention, in the control device, the measured value at which the current flowing through the electric wire by the measurement circuit can be regarded as a value 0 during the current detection operation is the first predetermined time or longer. The abnormality determination operation may be performed by turning off the switch when the measurement is continuously performed. By performing the abnormality determination operation when there is a possibility that the winding of the current transformer is broken in the current detection operation, it is possible to detect the disconnection of the winding at an early stage while executing the current detection operation.

Further, in the current detection device of the present invention, the control device can usually be used as the abnormality determination operation in a state where the switch is turned off and the load is not electrically connected to the electric wire by the measurement circuit. When no measured value is continuously measured for a second predetermined time or longer, it may be determined that the current transformer is disconnected.

Further, in the current detector of the present invention, one of the two voltage lines in the three-phase single-wire power system having two voltage lines and one neutral line and the neutral line Used in an interconnected distributed generation system, the current transformer may be attached to each of the two voltage lines. In the current detection device of the present invention, even if the internal load of the distributed power supply system cannot be connected to the voltage line not connected to the distributed power supply system, the current transformer attached to the voltage line not connected to the distributed power supply system. It is possible to determine the presence or absence of an abnormality in.

Further, in the current detection device of the present invention, when the control device determines that the current transformer has a disconnection in the abnormality determination operation, it may notify that an abnormality has occurred in the current transformer. Good. In this way, it is possible to quickly deal with the occurrence of an abnormality.

It is a block diagram which shows the outline of the structure of the distributed power generation system 20 including the current detection device 30 of this embodiment. It is a block diagram which shows the outline of the structure of the current detection device 30. It is a flowchart which shows an example of the CT disconnection detection process executed by the control device 50.

A mode for carrying out the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram showing an outline of the configuration of a distributed power generation system 20 including the current detection device 30 of the present embodiment. The distributed power generation system 20 is configured as a system connected to two wires, one voltage line and a neutral wire, out of three electric wires of the single-phase three-wire commercial power system 10. For example, when the distributed power generation system 20 is installed outdoors, the distributed power generation system 20 can be connected to the commercial power system 10 by using an outdoor outlet, and work for drawing a single-phase three-wire outdoors can be performed. Not needed. Hereinafter, of the three electric wires of the commercial power system 10, the neutral wire is also referred to as N phase 12n, one of the two voltage wires is also referred to as U phase (voltage phase) 12u, and the other of the two voltage wires is V phase (voltage). Phase) Also called 12v. The N-phase 12n is grounded by a pole transformer (not shown). In FIG. 1, a home load (external load) 14u is connected between the U phase and the N phase, and a home load (external load) 14v is connected between the V phase and the N phase.

In the present embodiment, the distributed power generation system 20 is a system in which a reverse current to the commercial power system 10 is not allowed. As shown in FIG. 1, the power generation device 22 for generating DC power and the power generation of the power generation device 22 Two voltage lines (U phase): a power conditioner 24 that converts power into AC power, a disconnection relay 26 that interconnects / disconnects the commercial power system 10, and a commercial power system 10 for power flow monitoring. A current detection device 30 for detecting the current flowing through the 12u, V-phase 12v) and a control device 50 for controlling the entire system are provided.

The power generation device 22 includes, for example, a solid oxide fuel cell, an evaporator, a reformer, and the like, and generates power by reforming gas (hydrogen gas) generated by reforming the raw material fuel gas and oxidant gas. It is configured as a fuel cell device. The power generation device 22 may be configured by a combination of a prime mover (gas engine, gas turbine, etc.) and a generator that generates electricity by power from the prime mover.

The power conditioner 24 includes a DC / DC converter that converts the voltage of the DC power generated by the power generation device 22, and an inverter that converts the DC power output from the DC / DC converter into AC power. The two output lines of the inverter are connected to either the U phase 12u or the V phase 12v of the commercial power system 10 and the N phase 12n via the disconnection relay 26.

The current detection device 30 is a CT measurement circuit connected between a CT (Current Transformer) 31 attached to two voltage lines (U phase 12u, V phase 12v) of the commercial power system 10 and a winding terminal of the CT 31, respectively. 40 and. FIG. 2 is a configuration diagram showing an outline of the configuration of the current detection device 30. As shown in FIG. 2, the CT measurement circuit 40 has voltage dividing resistors R1, R2, which are connected in series to the voltage source Vcc1 (for example, 5V voltage source) and the voltage source Vcc2 (for example, 2.5V voltage source). A transistor 42 as a switch interposed between R3 and R4, a voltage dividing resistor R1 and a voltage dividing resistor R2, and an inverting input terminal are connected to a connection point between the voltage dividing resistor R1 and the transistor 42 via an input resistor R5. The operational amplifier 41 whose non-inverting input terminal is connected to the connection point between the voltage dividing resistor R3 and the voltage dividing resistor R4, the feedback resistor R6 connected to the output terminal and the inverting input terminal of the operational amplifier 41, and the feedback resistor A feedback capacitor C connected in parallel with R6 is provided.

The CT31 is configured as a through-type current transformer in the present embodiment, and one terminal P1 of the winding is connected to a connection point between the voltage dividing resistor R1 and the transistor 42, and the other terminal of the winding is connected. P2 is connected to the connection point between the voltage dividing resistor R2 and the voltage dividing resistor R3.

Although not shown, the control device 50 is configured as a microprocessor centered on a CPU, and includes a ROM for storing a processing program, a RAM as a work memory, an input / output port, and the like, in addition to the CPU. A measurement signal (system current measurement value Ict) from the output terminal of the CT measurement circuit 40 (op amp 41) is input to the control device 50 via an AD converter (ADC) 51. On the other hand, the control device 50 outputs a control signal to the power generation device 22, a control signal to the power conditioner 24, an on / off signal to the disconnection relay 26, an on / off signal to the transistor 42 of each CT measurement circuit 40, and the like. ing.

Next, the operation of the current detection device 30 included in the distributed power generation system 20 configured in this way will be described.

The control device 50 turns on the transistor 42 of the CT measurement circuit 40 connected between the windings of the CT 31 in a state where the CT 31 is attached to the U phase 12u and the V phase 12v of the commercial power system 10, respectively, and the state thereof. A current detection operation for detecting the current flowing through the U-phase 12u and the V-phase 12v is performed based on the system current measurement value Ict measured by the CT measurement circuit 40, and the power flow direction is monitored based on each detected current. Then, when it is determined that reverse power flow (flow of active power from the distributed power generation system 20 to the commercial power system 10) has occurred, the disconnection relay 26 is turned off to disconnect the distributed power generation system 20 from the commercial power system 10. This makes it possible to prevent reverse power flow in the distributed power generation system 20 in which reverse power flow is not allowed.

Next, an operation (abnormality detection operation) for detecting the presence or absence of disconnection of the CT31 (winding wire) will be described. FIG. 3 is a flowchart showing an example of CT disconnection detection processing executed by the control device 50. This process is performed for a predetermined time in each of the current detection device 30 in which the CT 31 is attached to the U phase 12u and the current detection device 30 in which the CT 31 is attached to the V phase 12v while the above-mentioned current detection operation is being executed. It is executed repeatedly every time.

When the CT disconnection detection process is executed, the system current measurement value Ict measured by the CT measurement circuit 40 is input (step S100), and whether or not the input system current measurement value Ict is equal to or less than the first threshold value Iref1 is determined. Determine (step S110). Here, the first threshold value Iref1 is a measured value in which the current value flowing through the electric wire (voltage line) to which the CT31 is attached can be regarded as a value 0, and a value obtained in advance experimentally or by calculation is determined. There is. Here, the case where the CT 31 cannot detect the current is considered to be a case where the household load is not electrically connected to the electric wire to which the CT 31 is attached and a case where the CT 31 is disconnected.

If it is determined that the system current measured value Ict is not equal to or less than the first threshold value Reset 1 but larger than the first threshold value Reset 1, a current is flowing through the electric wire to which the CT 31 is attached, and it is determined that the CT 31 is normal, and the first counter Cnt1 Is reset to the value 0 (step S120), and this process ends. On the other hand, if it is determined that the system current measured value Ict is equal to or less than the first threshold value Iref1, then it is determined whether or not the first counter Cnt1 is equal to or greater than the first threshold value Clef1 (step S130). Here, the first threshold value Clef1 is predetermined as a value corresponding to the time required for determining that no current is flowing through the electric wire to which the CT31 is attached. If it is determined that the first counter Cnt1 is not equal to or higher than the first threshold value Clef1, the first counter Cnt1 is incremented by a value of 1 (step S140), the process returns to step S100, and the process is repeated. Then, in the process of repeating the process, if it is determined in step S130 that the first counter Cnt1 is equal to or higher than the first threshold value Clef1, the household load is electrically applied to the electric wire to which the CT31 is attached, whether the CT31 is broken or not. Execute the following processing to determine whether it is not connected (whether it is in a no-load state).

That is, first, the transistor 42 is turned off (step S160), the system current measurement value Ict measured by the CT measurement circuit 40 is input (step S170), and the input system current measurement value Ict is equal to or higher than the second threshold value Iref2. Whether or not it is determined (step S180). Here, the second threshold value Iref2 is a threshold value for determining whether the CT 31 is disconnected or in a no-load state, and a value obtained in advance experimentally or by calculation is determined.

If it is determined that the system current measured value Ict is not equal to or higher than the second threshold value Reset2, it is determined that the household load is not electrically connected to the electric wire to which the CT31 is attached, and the CT31 is not disconnected. The second counter Cnt2 is reset to a value of 0 (step S190), the transistor 42 is turned on (step S200), and this process ends. On the other hand, if it is determined that the system current measured value Ict is equal to or greater than the second threshold Iref2, then it is determined whether or not the second counter Cnt2 is equal to or greater than the second threshold Cref2 (step S210). Here, the second threshold value Clef2 is predetermined as a value corresponding to the time required to determine that the winding of the CT31 is broken. If it is determined that the second counter Cnt2 is not equal to or higher than the second threshold value Clef2, the second counter Cnt2 is incremented by a value of 1 (step S220), the process returns to step S170, and the process is repeated. Then, in the process of repeating the process, if it is determined in step S210 that the second counter Cnt2 is equal to or higher than the second threshold value Clef2, it is determined that the CT31 is disconnected, and the second counter Cnt2 is reset to a value of 0 ( Step S230), a warning is displayed on the display 52 (step S240), the transistor 42 is turned on (step S250), and this process ends.

Now, consider a case where the presence or absence of disconnection of the CT 31 is determined by using the current detection device of the comparative example which does not include the transistor 42 in the configuration shown in FIG. As described above, the cases where the CT31 cannot detect the current include the case where the household load is not electrically connected to the electric wire to which the CT31 is attached and the case where the winding of the CT31 is broken. Can be considered. Therefore, in determining whether or not the winding is broken based on the system current measurement value Ict measured by the CT measurement circuit 40 connected between the terminals of the winding of the CT 31, it is necessary to distinguish between the two. Occurs. The winding of the CT31 is connected in parallel with the voltage dividing resistor R2 to the voltage sources Vcc1 and Vcc2, and considering the winding resistance R0, there are cases where the CT31 is disconnected and cases where the disconnection is not generated. Since the combined impedance between the terminals of the winding of the CT31 changes, in the current detection device of the comparative example, the presence or absence of disconnection of the winding is determined by measuring the voltage change generated in response to the change of the combined resistance with the CT measurement circuit. You can think of making a decision. However, since the resistance value of the winding resistance R0 is generally significantly larger than the resistance value of the voltage dividing resistor R2, the degree of change in the combined impedance is small, and the system current measured by the CT measurement circuit 40. It is difficult to determine whether or not the winding of the CT31 is broken by the measured value Ict.

On the other hand, in the current detection device 30 of the present embodiment, the transistor 42 is turned off and the voltage dividing resistor R2 connected between the terminals of the windings of the CT 31 is disconnected, so that the windings are broken. It is possible to cause a large change in the potential input to the input terminal of the operational amplifier 41 depending on whether the wire is broken or not. That is, as shown in FIG. 2, in the state where the transistor 42 is turned off, if the winding of the CT 31 is not broken, the winding resistance R0 and the voltage dividing resistance R1 with respect to the voltage sources Vcc1 and Vcc2. The voltage divided by R3 and R4 acts on the non-inverting input terminal of the operational amplifier 41, whereas when the winding of the CT 31 is broken, the voltage of the voltage source Vcc2 is the non-inverting input terminal of the operational amplifier 41. Since it acts directly on the inverting input terminal, it is possible to detect the presence or absence of disconnection of the winding of the CT 31 by measuring these states with the CT measuring circuit 40.

In the current detection device 30 of the embodiment described above, in the CT measurement circuit 40, between the voltage dividing resistors R1 and the voltage dividing resistors R2 of the voltage dividing resistors R1 to R4 connected in series with the voltage sources Vcc1 and Vcc2. The transistor 42 is provided so as to intervene. Then, a current detection operation that detects the current flowing through the electric wire (U phase 12u or V phase 12v) to which the CT 31 is attached based on the system current measurement value Ict measured by the CT measurement circuit 40 with the transistor 42 turned on. With the transistor 42 turned off, an abnormality determination operation for determining the presence or absence of disconnection of the CT 31 is performed based on the system current measurement value Ict measured by the CT measurement circuit 40. As a result, the presence or absence of disconnection of the CT 31 can be appropriately determined by a simple configuration in which a switch is provided for the conventional current detection device.

In the embodiment, when it is determined that the winding of the CT 31 is broken, a warning is displayed on the display 52, but when the distributed power generation system 20 is connected to the server of the management company via the network. May transmit to the server that an abnormality has occurred in CT31.

In the embodiment, the current detection device of the present invention has been described by applying it to the distributed power generation system 20 in which reverse power flow is not allowed, but it may be applied to the distributed power generation system in which reverse power flow is allowed. The load may be applied to any device as long as it detects the current flowing through the connectable and disconnectable wires.

The correspondence between the main elements of the embodiment and the main elements of the invention described in the column of means for solving the problem will be described. In the embodiment, the domestic loads 14u and 14v correspond to the "load", the U-phase 12u and V-phase 12v correspond to the "electric wire", the CT31 corresponds to the "current transformer", and the voltage sources Vcc1 and Vcc2 correspond to each other. The voltage source corresponds to the voltage dividing resistor R2, the voltage dividing resistor R2 corresponds to the voltage dividing resistor, the CT measurement circuit 40 corresponds to the "measurement circuit", the transistor 42 corresponds to the "switch", and the control device 50 corresponds to the "switch". Corresponds to "control device".

Regarding the correspondence between the main elements of the embodiment and the main elements of the invention described in the column of means for solving the problem, the invention described in the column of means for the embodiment to solve the problem is carried out. Since it is an example for specifically explaining the form for solving the problem, the elements of the invention described in the column of means for solving the problem are not limited. That is, the interpretation of the invention described in the column of means for solving the problem should be performed based on the description in the column, and the embodiment is the invention described in the column of means for solving the problem. It is just a concrete example.

Although the embodiments for carrying out the present invention have been described above using the embodiments, the present invention is not limited to these embodiments, and various embodiments are used without departing from the gist of the present invention. Of course, it can be done.

The present invention can be used in the manufacturing industry of current detectors and distributed power generation systems.

10 Commercial power system, 12u U phase, 12v V phase, 12n N phase, 14u, 14v domestic load, 20 distributed power generation system, 22 power generation equipment, 24 power conditioner, 26 disconnection relay, 30 current detector, 31 CT, 40 CT measurement circuit, 41 operational amplifier, 42 transistor, 50 controller, 51 ADC (AD converter) 52 display, R0 winding resistor, R1, R2, R3, R4 voltage dividing resistor, R5 input resistor, R6 feedback resistor , C feedback capacitor, Vcc1, Vcc2 voltage source.

Claims (5)

A current detector that detects the current flowing through an electric wire whose load can be electrically connected and disconnected.
The current transformer attached to the electric wire and
A measuring circuit having a voltage dividing resistor connected between the terminals of the winding of the current transformer and connected in parallel with the winding with respect to the voltage source.
A switch connected in series with the voltage dividing resistor to the voltage source and connected in parallel with the winding.
A current detection operation for detecting the current flowing through the electric wire based on the measured value measured by the measuring circuit with the switch turned on is performed, and the measurement measured by the measuring circuit with the switch turned off. A control device that performs an abnormality determination operation to determine the presence or absence of disconnection of the current transformer based on the value, and
A current detector equipped with. The current detection device according to claim 1.
While the control device is performing the current detection operation, a measured value that can be regarded as a value 0 of the current flowing through the electric wire by the measuring circuit is continuously measured for a first predetermined time or more. Occasionally, the switch is turned off to perform the abnormality determination operation.
Current detector. The current detection device according to claim 1 or 2.
In the control device, as the abnormality determination operation, a measured value that cannot normally be obtained when the load is not electrically connected to the electric wire by the measuring circuit with the switch turned off becomes a second predetermined time or more. It is determined that the current transformer has a disconnection when continuously measured over a period of time.
Current detector. The current detection device according to any one of claims 1 to 3.
Used in a distributed power system connected to one of the two voltage lines and the neutral line in a three-phase single-wire power system having two voltage lines and one neutral line. Be,
The current transformer is attached to each of the two voltage lines.
Current detector. The current detection device according to any one of claims 1 to 4.
When the control device determines that the current transformer has a disconnection in the abnormality determination operation, it notifies that an abnormality has occurred in the current transformer.
Current detector.

Images