JP2018105798A - Current measurement system and power distribution board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current measurement system and a power distribution board with which it is possible to demagnetize a magnetized core.SOLUTION: A current measurement system 2 comprises: a core 50 having an open hole 500 for putting through a conductive member (conductive bar 84) in which a primary AC current flows; a coil 60 wound around the core 50; a secondary side circuit 90 including a load resistor 101 and having first and second terminals 901, 902, each of the first and second terminals 901, 902 being connected to both ends of the coil 60 without via other resistive elements; and a measurement unit 102 for measuring a primary current on the basis of a detection voltage developing across the load resistor 101. In the secondary side circuit 90, the load resistor 101 is connected between the first and second terminals 901, 902 without being connected to the other resistive elements in series. The secondary side circuit 90 is equipped with a resistance adjustment unit 4 for causing an electric resistance value between the first and second terminals 901, 902 in the secondary side circuit 90 to change.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a current measurement system and a distribution board, and more particularly, to a current measurement system including a core having a through hole for passing a conductive member through which a current flows, and a distribution board including the current measurement system.

  Conventionally, a distribution board has been proposed in which a main breaker, a branch breaker, and a terminal block are housed in a cabinet (housing) (see, for example, Patent Document 1).

  In the distribution board described in Patent Document 1, the terminal block includes a primary terminal, a secondary terminal, a conductive block that electrically connects the primary terminal and the secondary terminal, and a current flowing through the conductive block. It consists of a current transformer to measure. In this terminal block, a branch breaker or a main breaker to be subjected to current measurement is connected to a primary terminal or a secondary terminal, so that a current (main current or branch current) flowing through the conductive block is transferred by a current transformer. taking measurement.

JP 2011-36034 A

  In a current transformer, when a large current such as a short-circuit current flows through a conductive block (conductive member), the current transformer's magnetic core (core) may be magnetized and magnetized. May not be able to be detected accurately.

  The present invention has been made in view of the above problems, and an object thereof is to provide a current measurement system capable of demagnetizing a magnetized core and a distribution board including the current measurement system.

  A current measurement system according to an aspect of the present invention includes a core, a coil, a secondary circuit, and a measurement unit. The core has a through hole for passing a conductive member through which an alternating primary current flows. The coil is wound around the core. The secondary side circuit includes a burden resistor. The secondary circuit has first and second ends. In the secondary side circuit, the first and second ends are respectively connected to both ends of the coil without passing through other resistance elements. The measurement unit measures the primary current based on a detection voltage generated between both ends of the burden resistor. In the secondary circuit, the burden resistor is connected between the first and second ends without being connected in series with another resistance element. The secondary side circuit includes a resistance adjusting unit that changes an electrical resistance value between the first and second ends in the secondary side circuit.

  A distribution board according to an aspect of the present invention includes the current measurement system, the conductive member, and a cabinet that houses at least the conductive member.

  The present invention has an advantage that a current measuring system capable of demagnetizing a magnetized core and a distribution board equipped with the current measuring system can be provided.

FIG. 1 is a schematic configuration diagram of a current measurement system according to an embodiment. FIG. 2 is a front view of the same current measurement system and distribution board. FIG. 3 is a block diagram showing the configurations of the current measurement system and the distribution board. FIG. 4 is a perspective view showing a current transformer and a conductive member provided in the current measurement system. FIG. 5 is a BH curve diagram of the core for explaining the relationship between the magnetic field applied to the core of the current transformer and the magnetic flux density generated in the core. FIG. 6 is a schematic configuration diagram of a current measurement system according to the first modification. FIG. 7 is a BH curve diagram of the core for explaining the relationship between the magnetic field applied to the core of the current transformer and the magnetic flux density generated in the core. FIG. 8 is a schematic configuration diagram of a current measurement system according to the second modification. FIG. 9 is a schematic configuration diagram of a current measurement system according to the third modification.

  The embodiment described below is only one of various embodiments of the present invention. Embodiments of the present invention are not limited to the following embodiments, and may include other embodiments. In addition, the following embodiments can be variously changed according to the design or the like as long as they do not depart from the technical idea according to the present invention.

(1) Embodiment Hereinafter, a current measurement system 2 according to the present embodiment and a distribution board 1 including the current measurement system 2 will be described with reference to FIGS.

  The current measurement system 2 of the present embodiment is used in a power measurement system for measuring at least one of power consumption and power consumption in a customer facility. The current measurement system 2 measures a current (primary current) flowing through a conductive bar 84 (described later) in the distribution board 1. The power measurement system performs an operation for obtaining at least one of power consumption and power consumption based on the primary current measured by the current measurement system 2 and the line voltage of two power lines 81 (described later). Do. The term “customer facility” as used herein means a facility of an electric power consumer, not only a facility that receives power supply from an electric power company such as an electric power company, but also a private power generation facility such as a solar power generation facility. Includes facilities that receive power. In this embodiment, a non-residential facility such as a store or an office will be described as an example of a customer facility. However, the present invention is not limited to this example, and the consumer facility may be an apartment house, a detached house, an apartment house of an apartment house, or the like.

(1.1) Distribution board Here, first, the basic configuration of the distribution board 1 including the current measurement system 2 will be described with reference to FIG. In the present embodiment, a distribution board 1 having a single-phase three-wire system capable of taking out AC 100 [V] / 200 [V] will be described as an example.

  The distribution board 1 includes a cabinet 70. The distribution board 1 includes a main breaker 10, a plurality (18 in the example of FIG. 2) branch breakers (circuit breakers) 20, three conductive bars 84, and at least one (in the example of FIG. 2). 3) current sensors 30 are provided in the cabinet 70. In the following description, the upper, lower, left and right, front and rear (up and down, left and right, front and back indicated by arrows in FIG. In this case, the front-rear direction is defined as a “first direction” that is the thickness direction of the conductive bar 84. Further, the left-right direction is defined as a “second direction” orthogonal to the first direction. However, the mounting direction of the distribution board 1 and the current sensor 30 is not limited to the direction indicated by the arrow in FIG. In each figure, the arrows with up / down, left / right, and front / rear are arrows for indicating directions and are not accompanied by an entity.

  The cabinet 70 is formed in a box shape having an opening 71 on the front surface. The cabinet 70 is formed in a rectangular shape that is long in the vertical direction when viewed from the front (viewed from the front). Rail members 73 extending in the vertical direction are respectively installed on the left and right sides of the bottom plate 72 of the cabinet 70. A first mounting plate 74 and a second mounting plate 75 are fixed to the pair of rail members 73. Each of the first mounting plate 74 and the second mounting plate 75 is installed so as to be bridged between the pair of rail members 73. The first mounting plate 74 is disposed above the second mounting plate 75. A synthetic resin mounting base 76 is fixed to the front surface of the second mounting plate 75.

  The main breaker 10 is housed in the cabinet 70 by being attached to the front surface of the first attachment plate 74. The plurality of branch breakers 20 are housed in the cabinet 70 by being attached to the attachment base 76. The cabinet 70 may include a door that closes the opening 71.

  The primary side terminal 11 of the main breaker 10 is electrically connected to an AC power source 200 (see FIG. 3) via a three-wire power line (trunk line) 81. Three bus conductors 82 (see FIGS. 2 and 3) of L1, L2, and N phases are electrically connected to the secondary terminal 12 of the main breaker 10. The L1-phase, L2-phase, and N-phase bus conductors 82 are electrically connected to the L1-phase, L2-phase, and N-phase power lines 81 on a one-to-one basis. Each of the three bus conductors 82 includes a connecting member (joint bar) 83 that is directly connected to the main breaker 10, and the conductive bar 84 that is connected to the main breaker 10 via the connecting member 83. Yes.

  Each of the three conductive bars 84 is formed in a long flat plate shape (band shape) with a conductive material such as copper, for example. Here, the three conductive bars 84 correspond to the L1, L2, and N phases, respectively. The three conductive bars 84 are held by the mounting base 76 in a direction in which each longitudinal direction coincides with the vertical direction and each thickness direction coincides with the front-rear direction (first direction). The three conductive bars 84 are attached to the center of the attachment base 76 in the left-right direction so as to be arranged in the front-rear direction (each thickness direction) with an appropriate interval in front of the attachment base 76. In the present embodiment, the three conductive bars 84 are attached to the central portion of the attachment base 76 in the left-right direction, but the attachment positions of the conductive bars 84 are not limited to the above positions. The three conductive bars 84 may be attached at positions shifted from the center position in the left-right direction on the attachment base 76.

  In the present embodiment, the three conductive bars 84 are arranged in the order of the L1 phase, the N phase, and the L2 phase from the front in the front-rear direction. Here, each of the three conductive bars 84 is located above and below the mounting base 76 so that the three conductive bars 84 are positioned across the vertical ends of the mounting base 76 in front of the mounting base 76. It is formed longer than the dimension in the direction.

  Each of the three connecting members 83 is made of a conductive material such as copper, for example. The three connecting members 83 electrically connect the three conductive bars 84 and the secondary side terminals 12 of the main breaker 10 respectively.

  The plurality of branch breakers 20 are electrically connected to the secondary terminal 12 of the main breaker 10 via the bus conductor 82 by being connected to the conductive bar 84. Each branch breaker 20 is attached to attachment spaces provided on both sides (left side and right side) of the conductive bar 84 in the short direction (left and right direction) of the front surface of the attachment base 76. The mounting base 76 is provided with a plurality of mounting structures for holding the plurality of branch breakers 20 respectively.

  Each branch breaker 20 includes a power supply terminal and a load terminal. A power supply terminal of each branch breaker 20 is electrically connected to the conductive bar 84, and a branch circuit is connected to a load terminal of each branch breaker 20. Each branch breaker 20 has a slit on the center side in the left-right direction, into which the three conductive bars 84 are inserted. Three slits are provided so as to correspond to the three conductive bars 84. The power supply terminal of each branch breaker 20 is provided so as to be exposed in two of the three slits. Thereby, in the state where each branch breaker 20 is attached to the attachment base 76, the conductive bar 84 is inserted into the slit, and the power supply terminal is electrically connected to the conductive bar 84.

  In the branch breaker 20 for 100 [V] connected to the N phase and the L1 phase, a power supply terminal is provided in each of the slit corresponding to the N-phase conductive bar 84 and the L1-phase conductive bar 84. The branch breaker for 100 [V] connected to the N phase and the L2 phase is provided with a power supply terminal at each of the slits corresponding to the N phase conductive bar 84 and the L2 phase conductive bar 84. The branch breaker 20 for 200 [V] connected to the L1 phase and the L2 phase is provided with a power supply terminal in each of the slits corresponding to the L1 phase conductive bar 84 and the L2 phase conductive bar 84.

  In the present embodiment, the current sensor 30 is attached to the attachment base 76 in the same manner as the plurality of branch breakers 20. The current sensor 30 is housed in the cabinet 70 by attaching the attachment base 76 to the front surface of the second attachment plate 75.

(1.2) Current Sensor Next, the current sensor 30 provided in the current measurement system 2 will be described with reference to FIGS.

  The current measurement system 2 includes at least one current sensor 30. As shown in FIG. 2, in the present embodiment, the current measurement system 2 includes a plurality (specifically, three) of current sensors 31 to 33.

  In the present embodiment, the 18 branch breakers 20 are divided into a plurality of breaker groups G1 to G3. Specifically, the 18 branch breakers 20 are divided into breaker groups G1 to G3 in units of six in the longitudinal direction (vertical direction) of the conductive bar 84. The breaker groups G1 to G3 are arranged in order from the main breaker 10 side of the conductive bar 84 so that the breaker group G1 is closest to the main breaker 10 and the breaker group G3 is farthest from the main breaker 10 among the breaker groups G1 to G3. It is out.

  The current sensor 31 is disposed between the main breaker 10 and the breaker group G1, the current sensor 32 is disposed between the breaker group G1 and the breaker group G2, and the current sensor 33 is disposed between the breaker group G2 and the breaker group G3. Is installed. Thereby, in the current sensor 31, the current flowing through the breaker groups G1 to G3 can be measured. On the other hand, the current sensor 32 can measure the current flowing through the breaker groups G2 and G3, and the current sensor 33 can measure the current flowing through the breaker group G3.

  In the current measurement system 2, for a bipolar (two-pole) having two cores 50 and two coils 60 so that the current flowing through each of the two bus conductors 82 can be measured by one current sensor 30. A current sensor 30 is used. However, even in the case of the current sensor 30 for multiple poles, the basic configuration is the same as that of the current sensor 30 for single poles having one core 50 and one coil 60. The current sensor 30 will be described.

  The single-pole current sensor 30 uses one of the three conductive bars 84 as a current measurement target, and detects a current (primary current) flowing through the conductive bar 84 as a current measurement target in a non-contact manner. That is, an electrical signal corresponding to the current flowing through the conductive bar 84 is output from one coil 60 in the current sensor 30. Here, among the three conductive bars 84, the conductive bar 84 that is a current measurement target of the current sensor 30 is defined as a “conductive member”. Here, the case where the current measurement target is the L1-phase conductive bar 84, that is, the case where the L1-phase conductive bar 84 is the “conductive member” is illustrated.

  The core 50 is made of a magnetic material such as ferrite, for example. As shown in FIG. 4, the core 50 has a through hole 500 through which one conductive member (conductive bar 84) passes. The core 50 has a conductive bar 84 passed through the through hole 500. A surrounding magnetic path is formed. For example, the core 50 is formed so that a cross-sectional shape orthogonal to the vertical direction is a rectangular frame shape that is long in the horizontal direction. In other words, the core 50 is formed in a shape in which the dimension in the left-right direction is larger than the dimension in the front-rear direction.

  In this embodiment, the core 50 is divided into a first core 51 and a second core 52 in the left-right direction. The first core 51 includes a central piece 512 extending in the front-rear direction, and a first leg piece 513 and a second leg piece 514 that protrude rightward from both ends of the central piece 512 in the front-rear direction. Yes. The second core 52 includes a center piece 522 extending in the front-rear direction, and a first leg piece 523 and a second leg piece 524 that project leftward from both ends of the center piece 522 in the front-rear direction. Yes.

  In the left-right direction, the end surfaces of the first and second leg pieces 513 and 514 of the first core 51 and the end surfaces of the first and second leg pieces 523 and 524 of the second core 52 are brought into contact with each other, respectively. A through hole 500 is formed between the first core 51 and the second core 52. A conductive member (conductive bar 84) that is a current measurement target is inserted into the through hole 500, and a closed magnetic circuit that surrounds the conductive member (conductive bar 84) is formed by the first core 51 and the second core 52.

  A coil 60 is wound around at least a part of the core 50. When the number of turns of the coil 60 is n, the core 50, the conductive member (conductive bar 84), and the coil 60 constitute a transformer having a turn ratio of 1: n. That is, the current sensor 30 functions as a CT (Current Transformer) sensor that outputs an electrical signal corresponding to the current flowing through the conductive bar 84 inserted through the through hole 500 from the coil 60.

  In the present embodiment, the coil 60 includes a first coil 61 and a second coil 62. The first coil 61 is wound around the first leg piece 523 of the second core 52, and the second coil 62 is wound around the second leg piece 524 of the second core 52. The first coil 61 and the second coil 62 are electrically connected in series.

  Here, in the coil 60, the first coil 61 is added such that the induced current generated in the first coil 61 due to the current flowing through the conductive member (conductive bar 84) and the induced current generated in the second coil 62 are added. And the winding direction and connection relation of the second coil 62 are set. That is, the flowing direction of the induced current (secondary current) caused by the current flowing through the conductive bar 84 (primary current) is the same between the first coil 61 and the second coil 62 between both ends of the coil 60. Become. Specifically, the magnetic flux generated by the current flowing through the conductive bar 84 is reversed between the first leg piece 523 and the second leg piece 524. Therefore, for example, when the first coil 61 and the second coil 62 are connected so that the winding start of the second coil 62 is connected to the winding end of the first coil 61, the first coil 61 and the second coil 62 Then, the winding direction in the right side view is reversed. The first coil 61 and the second coil 62 may be electrically connected by, for example, an electric wire, or may be electrically connected via a printed wiring board or the like.

(1.3) Current Measurement System Next, the configuration of the current measurement system 2 using the bipolar current sensor 30 will be described with reference to FIGS.

  The current measurement system 2 includes a measurement device 100 in addition to at least one current sensor 30 (three current sensors 31 to 33 in the present embodiment). Each of the current sensors 31 to 33 is electrically connected to the measurement device 100 via a plurality (four) of electric wires 64.

  As shown in FIG. 1, the measuring device 100 includes at least one burden resistor 101 and a measuring unit 102. The measuring apparatus 100 includes the same number of burden resistors 101 as the number of cores 50 (the number of coils 60). In FIG. 1, one core 50 among the six cores 50 included in the current measurement system 2 and a burden resistor 101 corresponding to the core 50 are illustrated. As shown in FIG. 1, the burden resistor 101 is connected between both ends of the corresponding coil 60 without being connected in series with another resistance element. Here, the resistance element means an element such as a resistor (fixed resistor, variable resistor, thermistor), for example, and does not include a resistance component of a conductor only for wiring. Therefore, the electric wire 64 that connects the coil 60 and the burden resistor 101 does not correspond to a resistance element.

  Both ends of the load resistor 101 are connected to the measuring unit 102. The measurement unit 102 is connected to circuit ground (reference potential, zero potential). The measuring unit 102 connects one end of the burden resistor 101 to the circuit ground, and measures a voltage generated between the other end of the burden resistor 101 and the circuit ground as a both-end voltage (detection voltage) of the burden resistor 101. That is, the measuring unit 102 measures a detection voltage generated between both ends of the burden resistor 101, and obtains a current (primary current) flowing through the conductive bar 84 corresponding to the burden resistor 101 based on the measured detection voltage.

  More specifically, when a current (primary current) flows through the conductive bar 84, a magnetic field corresponding to the primary current is generated around the conductive bar 84. When a magnetic field is generated around the conductive bar 84 in a state where the conductive bar 84 is passed through the through hole 500 of the core 50, a magnetic flux corresponding to the magnetic field is generated in the core 50. A voltage corresponding to the time change of the magnetic flux generated in the core 50 is generated in the coil 60, and an induced current (secondary current) flows in the coil 60 due to this voltage.

  The secondary current flows through the coil 60 in a direction in which a magnetic flux (called a canceling magnetic flux) in a direction opposite to the magnetic flux generated in the core 50 by the primary current (direction canceling the magnetic flux generated by the primary current) is generated in the core 50. . When the core 50 is not magnetically saturated, the magnitude of the secondary current is given by a value obtained by dividing the magnitude of the primary current by the number of turns n of the coil 60. When a secondary current flows through the coil 60, a voltage (detection voltage) proportional to the secondary current is generated between both ends of the burden resistor 101. Therefore, the measurement unit 102 can obtain the primary current by measuring the detection voltage generated between both ends of the burden resistor 101 based on the resistance between both ends of the burden resistor 101.

  Since the primary current flowing through the conductive bar 84 is an alternating current, the magnitude and direction of the magnetic field generated by the primary current change with time, and the magnetic flux in the core 50 also changes with time. Therefore, the magnetic flux generated in the core 50 (the sum of the magnetic flux generated by the primary current and the magnetic flux generated by the secondary current) also changes with time. The magnetic field H applied to the core 50 is relatively small because it is the sum of the magnetic field due to the primary current and the magnetic field due to the secondary current, and when the time change between the magnetic field H and the magnetic flux density B in the core 50 is plotted, the origin is centered. A closed curve (schematically shown in FIG. 5 by a two-dot chain line A1). As shown in FIG. 5, the value of the magnetic flux density B of the core 50 with respect to the same value of the magnetic field H differs between when the magnitude of the magnetic field H increases and when it decreases. That is, the magnetic flux density B of the core 50 exhibits hysteresis with respect to the magnetic field H.

  Here, for example, the load in the load circuit connected to the conductive bar 84 is short-circuited, so that a large current in one direction (for example, the direction from the AC power supply 200 to the load) (for example, the instantaneous value is about 5 kA). A large magnetic field is generated around the conductive bar 84. The magnetic flux density B in the core 50 is increased by this magnetic field (see the dotted line A2 in FIG. 5), the core 50 is magnetized, and the residual magnetic flux density is increased in the core 50 even if the primary current does not flow through the conductive bar 84. Remain. The magnetic flux density B in the core 50 is the sum of the component generated by the magnetic field H applied to the core 50 and the residual magnetic flux density. When the time change between the magnetic field H and the magnetic flux density B in the core 50 is plotted, what is the origin? This is a closed curve centered at a different point (shown schematically by a one-dot chain line A3 in FIG. 5). Therefore, when the core 50 is magnetized, accurate measurement of the primary current may be difficult due to the influence of the residual magnetic flux density.

  Therefore, the current measurement system 2 according to the present embodiment adjusts the resistance of the circuit connected between both ends of the coil 60 in order to reduce the residual magnetic flux density of the core 50 (demagnetize the core 50). Part 4 is provided. Hereinafter, the resistance adjusting unit 4 will be described with reference to FIG.

  In the present embodiment, the resistance adjusting unit 4 includes a burden resistance switch 40 connected in series with the burden resistor 101 between both ends of the coil 60. The load resistance switch 40 may be a mechanical switch (for example, a contact device having a movable contact and a fixed contact) or a semiconductor switch such as a transistor.

  In the present embodiment, the measurement apparatus 100 is provided with an operation unit 111 that receives an operation of an operator, such as a push button. In addition, the measuring apparatus 100 includes a control unit 112 that controls on / off of the burden resistance switch 40.

  The control unit 112 of the present embodiment has a normal mode and a demagnetization mode. The control unit 112 switches from the normal mode to the demagnetization mode in response to an operation on the operation unit 111 (for example, a push operation on a push button).

  In the normal mode, the control unit 112 keeps the burden resistance switch 40 on. That is, in the normal mode, the control unit 112 keeps the burden resistance switch 40 on, so that the electrical resistance value of the circuit connected between both ends of the coil 60 is substantially equal to the electrical resistance value of the burden resistance 101. The corresponding predetermined value is maintained. Strictly speaking, the electric wire 64 connecting the load resistor 101 and the coil 60 also has an electric resistance value, but is substantially smaller than the electric resistance value of the load resistor 101, so that the electric resistance value of the load resistor 101 is substantially reduced. It can be regarded as an electric resistance value of a circuit connected between both ends of the coil 60.

  In the demagnetization mode, the control unit 112 turns on after turning off the burden resistance switch 40. The time for which the control unit 112 turns off the burden resistance switch 40 is set to be longer than the half cycle of the primary current that is alternating current. That is, in the degaussing mode, the control unit 112 controls the resistance adjusting unit 4 to increase the electric resistance value of the circuit connected between both ends of the coil 60 from the normal mode value (the predetermined value). Later, the value is returned to the normal mode value (the predetermined value). In the present embodiment, the control unit 112 controls the burden resistance switch 40 in the degaussing mode to connect the burden resistor 101 between both ends of the coil 60 after opening both ends of the coil 60.

  When the electrical resistance value of the circuit connected between both ends of the coil 60 increases, the secondary current flowing through the coil 60 decreases and the magnetic field due to the secondary current also decreases. In this embodiment, since the burden resistance switch 40 is turned off, the electrical resistance value of the circuit connected between both ends of the coil 60 is ideally infinite, the secondary current becomes zero, and the secondary current The magnetic field generated by is also zero. Therefore, substantially only the magnetic field due to the primary current is applied to the core 50, and the magnetic flux density B in the core 50 changes according to the change of the magnetic field due to the primary current. For example, when the time change between the magnetic field H and the magnetic flux density B in the core 50 is plotted, it moves on a large closed curve (generally indicated by a dotted line A4 in FIG. 5) centering on the origin and including the curves A1 and A3. It will be. That is, the magnetic field applied to the core 50 becomes relatively large, and the magnetic flux density B in the core 50 that is biased in one direction (the positive direction of the Y axis in FIG. 5) in the BH curve is reversed (in FIG. 5). (The negative direction of the Y axis).

  Thereafter, by turning on the burden resistance switch 40 to connect the burden resistance 101 between both ends of the coil 60, a secondary current starts to flow through the coil 60, and a magnetic field due to the secondary current is applied to the core 50. In 50, a magnetic flux (cancellation magnetic flux) due to the secondary current is generated.

  Here, the measuring apparatus 100 according to the present embodiment further includes a zero-cross detecting unit 103 that detects a zero-cross of a voltage generated between both ends of the burden resistance switch 40 in order to determine a timing for turning on the burden resistance switch 40. In the degaussing mode, the control unit 112 turns on the burden resistance switch 40 when the magnetic flux density B generated in the core 50 becomes zero based on the detection result of the zero cross detection unit 103. For example, the control unit 112 obtains a time point at which the time change of the magnetic flux density B in the core 50 becomes zero from the detection result of the zero cross detection unit 103. The control unit 112 can determine when the magnetic flux density B generated in the core 50 becomes zero based on the obtained time point. The control unit 112 is configured such that when the magnetic flux density B in the core 50 becomes maximum in the positive direction and the time change becomes zero, and when the magnetic flux density B in the core 50 becomes maximum in the negative direction and the time change becomes zero. And when the magnetic flux density B generated in the core 50 becomes zero. Note that the timing at which the control unit 112 turns on the burden resistance switch 40 does not have to be strictly when the magnetic flux density B generated in the core 50 becomes zero, but to the extent that the magnetic flux density B generated in the core 50 can be regarded as zero. It may be small.

  When the magnetic flux density B in the core 50 is zero, the residual magnetic flux density of the core 50 can be regarded as zero (the core 50 is not magnetized). Therefore, the core 50 can be demagnetized by turning on the burden resistance switch 40 when the magnetic flux density B in the core 50 is zero.

  Further, the burden resistor 101 of the present embodiment is connected between both ends of the coil 60 without being connected in series with other resistance elements. The resistance value of the resistance element may vary due to the influence of temperature or the like, and the variation of the electrical resistance value may affect the measured value of the secondary current by the measurement unit 102. In the present embodiment, the burden resistor 101 is connected between both ends of the coil 60 without being connected in series with another resistor element (the only resistor element existing between both ends of the coil 60 is the burden resistor 101. Therefore, it is possible to avoid the influence of such other resistance elements.

  From another viewpoint, the current measurement system 2 of the present embodiment measures a current (primary current) flowing through a primary circuit including a conductive member (conductive bar 84). And the current measurement system 2 of this embodiment is provided with the secondary side circuit 90, as shown in FIG. The secondary circuit 90 is a circuit connected between both ends of the coil 60. The secondary-side circuit 90 has a first end 901 and a second end 902 that are connected to both ends of the coil 60 without passing through other resistance elements. The secondary circuit 90 includes a burden resistor 101 and a resistance adjustment unit 4. The burden resistor 101 is connected between the first end 901 and the second end 902 in the secondary circuit 90 without being connected in series with other resistance elements. The resistance adjustment unit 4 changes the electrical resistance value between the first end 901 and the second end 902 in the secondary circuit 90. In the present embodiment, the secondary side circuit 90 includes only the burden resistor 101 as a resistance element. In the present embodiment, the resistance adjusting unit 4 is the burden resistance switch 40 connected in series with the burden resistor 101 between the first end 901 and the second end 902.

  As described above, since the secondary side circuit 90 includes the resistance adjusting unit 4, the secondary current flowing through the secondary side circuit 90 can be reduced (set to zero), and the core 50 is caused by the secondary current. Such a magnetic field can be reduced (to zero). Therefore, even if the core 50 is magnetized, the magnetic flux density in the core 50 can be greatly varied by a relatively small primary current flowing through the conductive member (conductive bar 84), and the core 50 can be demagnetized. Become. Further, the burden resistor 101 is connected between the first end 901 and the second end 902 in the secondary circuit 90 without being connected in series with other resistance elements. That is, the closed circuit including the coil 60 and the burden resistor 101 does not include a resistance element other than the burden resistor 101. For this reason, when the measurement part 102 measures a secondary current, it does not receive to the influence of another resistive element.

  In addition, although the measuring device 100 is installed outside the cabinet 70 in this embodiment, it is not limited to this example and may be installed inside the cabinet 70. The measuring apparatus 100 includes a microcomputer having a processor and a memory, for example. Various functions of the measuring apparatus 100 (the control unit 112, the zero-crossing detection unit 103, etc.) are realized by the microcomputer processor executing the program recorded in the memory. The program executed by the processor of the measuring apparatus 100 may be recorded in advance in a memory of a microcomputer, may be provided by being recorded on a recording medium such as a memory card, or may be provided through an electric communication line. Also good.

(2) Modification A current measurement system 2 according to a modification will be described. Hereinafter, the embodiment described based on FIGS. 1 to 4 is referred to as a “basic example”. In each modification, the same components as those of the current measurement system 2 of the basic example are denoted by the same reference numerals, and description thereof will be omitted as appropriate. Moreover, the current measurement system 2 of each modification can be provided in the distribution board 1 in place of the current measurement system 2 of the basic example.

(2.1) Modification 1
FIG. 6 is a schematic configuration diagram of a current measurement system 2 according to the first modification. In addition to the burden resistance switch 40, the resistance adjustment unit 4 of the present modification includes a first resistance unit 410 and a second resistance unit 420. Each of the first resistance unit 410 and the second resistance unit 420 is connected in parallel to a series circuit of the burden resistor 101 and the burden resistor switch 40. The first resistor unit 410 includes a series circuit of a first resistor 411 and a first switch 412. The first resistor 411 has a larger electrical resistance value than the burden resistor 101. The second resistor unit 420 includes a series circuit of a second resistor 421 and a second switch 422. The second resistor 421 has a larger electrical resistance value than the first resistor 411.

  In this modification, the control unit 112 controls on / off of the burden resistance switch 40, the first switch 412, and the second switch 422.

  When the operation unit 111 is operated, the control unit 112 switches from the normal mode to the degaussing mode. In the normal mode, the control unit 112 maintains the burden resistance switch 40 on and maintains the first switch 412 and the second switch 422 off. That is, in the normal mode, the control unit 112 keeps the burden resistance switch 40 on and keeps the first switch 412 and the second switch 422 off, so that the electrical resistance of the circuit connected between both ends of the coil 60 is maintained. The value is substantially maintained at a predetermined value corresponding to the electric resistance value of the burden resistor 101.

  In the degaussing mode, the control unit 112 turns off the burden resistance switch 40, turns off the first switch 412, and turns on the second switch 422. Thereafter, the control unit 112 turns off the burden resistance switch 40, turns on the first switch 412, and turns off the second switch 422. Thereafter, the control unit 112 turns on the burden resistance switch 40, turns off the first switch, and turns off the second switch 422. As described above, by switching on / off the burden resistance switch 40, the first switch 412, and the second switch 422, the electrical resistance value of the circuit connected between both ends of the coil 60 in the demagnetization mode of the control unit 112 is changed to the first value. The electric resistance value of the two resistors 421, the electric resistance value of the first resistor 411, and the electric resistance value of the burden resistor 101 are decreased stepwise. As the electrical resistance value of the circuit connected between both ends of the coil 60 decreases stepwise, the secondary current flowing through the coil 60 increases stepwise, and the cancellation magnetic flux generated in the core 50 by the secondary current also increases. Will increase. Therefore, as schematically shown by a solid line A10 in FIG. 7, the magnitude of the magnetic flux density B in the core 50 is reduced stepwise, and thereby the residual magnetic flux density of the core 50 can be reduced stepwise. It becomes. 7 plots the time change between the magnetic field H applied to the core 50 and the magnetic flux density B in the core 50 when the burden resistance switch 40 and the first switch are turned off and the second switch 422 is turned on. It is a curved line.

  Note that the control unit 112 determines that the load resistance switch 40, the first resistance switch 40, and the first resistor so that a part of a period for maintaining only the second switch 422 and a part for a period for maintaining only the first switch 412 overlap. The on / off state of the switch 412 and the second switch 422 may be controlled. As a result, it is possible to prevent the two ends of the coil 60 from being released in a period between a period in which only the second switch 422 is on and a period in which only the first switch 412 is on.

(2.2) Modification 2
FIG. 8 is a schematic configuration diagram of the current measurement system 2 according to the second modification. In this modified example, the burden resistor 101 includes the variable resistor 43, and the burden resistor 101 functions as the resistance adjustment unit 4.

  The electrical resistance value of the burden resistor 101 (variable resistor 43) changes according to the operation of the operation unit 111 (for example, volume) provided in the measuring apparatus 100, for example. For example, when measuring the secondary current, the electric resistance value of the variable resistor 43 is set to the lowest value of the variable range. When the core 50 is magnetized, for example, the user decreases the canceling magnetic flux in the core 50 by increasing the electric resistance value of the variable resistor 43, and then gradually decreases the electric resistance value of the variable resistor 43. To gradually increase the canceling magnetic flux. Thereby, the core 50 can be demagnetized.

  In the current measurement system 2 of this modification, the electric resistance value of the variable resistor 43 changes according to the operation of the operation unit 111 by the operator, but the electric resistance value of the variable resistor 43 is controlled by the measuring device 100. A control unit 112 may be provided.

(2.3) Modification 3
FIG. 9 is a schematic configuration diagram of a current measurement system 2 according to Modification 3. In the present modification, the measuring apparatus 100 includes a determination unit 113. The determination unit 113 determines whether or not the magnitude of the primary current has exceeded a predetermined threshold value. For example, a shunt resistor is connected in series to the conductive member (conductive bar 84), and the determination unit 113 detects the magnitude of the primary current based on the voltage generated across the shunt resistor.

  When the determination unit 113 determines that the primary current has exceeded the threshold, the control unit 112 switches from the normal mode to the demagnetization mode, and turns on after the burden resistance switch 40 is turned off.

  Thereby, for example, when the primary current exceeds the threshold due to a short circuit of the load and the core 50 may be magnetized, the core 50 can be demagnetized without the user's hand.

  In this modification, the configuration in which the determination unit 113 is provided in the current measurement system 2 including the burden resistance switch 40 similar to the basic example is illustrated, but the current measurement similar to the modification 1 or the modification 2 is illustrated. The determination unit 113 may be provided in the system 2. Also in this modification, the operation unit 111 may be provided in the measurement apparatus 100.

(2.4) Other Modifications In one modification, the current measurement system 2 may change the magnitude (amplitude) of the primary current in the demagnetization mode of the control unit 112. For example, the current measurement system 2 may gradually decrease the magnitude (amplitude) of the primary current in the demagnetization mode of the control unit 112. If the magnitude of the primary current is increased, the magnetic field applied to the core 50 by the primary current also increases. Therefore, in this modification, the fluctuation | variation of the magnetic flux density B in the core 50 can be enlarged, and it becomes easier to demagnetize the core 50. FIG.

  In a modification, the operation unit 111 and the determination unit 113 may not be provided in the measurement apparatus 100 but may be provided outside the measurement apparatus 100.

  In the current measurement system 2 of the first modification, at least two of the burden resistance switch 40, the first switch 412 and the second switch 422 may be configured as c-contact switches capable of switching connection destinations. .

  In the current measurement system 2 of the basic example, the measurement unit 102 may measure the voltage across the series circuit of the burden resistor 101 and the burden resistor switch 40. In this case, the measurement unit 102 also functions as the zero cross detection unit 103.

  In the current measurement system 2 of Modification 1, the resistance adjustment unit 4 includes one or more other resistance units including a series circuit of a resistor and a switch in addition to the first resistance unit 410 and the second resistance unit 420. Also good. Each resistance unit is connected in parallel to a series circuit of the burden resistor 101 and the burden resistor switch 40.

(3) Aspect As described above, the current measurement system (2) according to the first aspect includes the core (50), the coil (60), the secondary side circuit (90), and the measurement unit (102). And comprising. The core (50) has a through hole (500) for passing a conductive member (conductive bar 84) through which an alternating primary current flows. The coil (60) is wound around the core (50). The secondary side circuit (90) includes a burden resistor (101). The secondary circuit (90) has first and second ends (901, 902). As for a secondary side circuit (90), the 1st and 2nd end (901,902) is each connected to the both ends of the coil (60) without passing through another resistance element. The measurement unit (102) measures the primary current based on the detection voltage generated across the burden resistor (101). In the secondary circuit (90), the burden resistor (101) is connected between the first and second ends (901, 902) without being connected in series with the other resistance elements. The secondary side circuit (90) includes a resistance adjusting unit (8) that changes an electric resistance value between the first and second ends (901, 902) in the secondary side circuit (90).

  According to this configuration, even when the core (50) is magnetized, the residual magnetic flux density of the core (50) is reduced by the primary current passing through the through hole (500) of the core (50), and the core (50 ) Can be demagnetized. Further, when the measuring unit 102 measures the secondary current, it is not affected by other resistance elements.

  The current measurement system (2) of the second aspect further includes a control unit (112) for controlling the resistance adjustment unit (4) in the first aspect. The control unit (112) has a normal mode and a demagnetization mode. In the normal mode, the control unit (112) maintains the electrical resistance value between the first and second ends (901, 902) in the secondary side circuit (90) at a predetermined value. In the degaussing mode, the control unit (112) increases the electrical resistance value between the first and second ends (901, 902) in the secondary side circuit (90) from a predetermined value, and then returns to the predetermined value. .

  According to this configuration, even if the core (50) is magnetized, the core (50) can be demagnetized by reducing the residual magnetic flux density of the core (50).

  In the current measurement system (2) of the third aspect, in the second aspect, the resistance adjustment unit (4) is connected in series with the burden resistance (101) between the first and second ends (901, 902). A burden resistance switch (40). The control unit (112) keeps the burden resistance switch (40) on in the normal mode. In the degaussing mode, the control unit (112) turns off the burden resistance switch (40) and then turns it on.

  According to this configuration, it is possible to demagnetize the core (50) by reducing the residual magnetic flux density of the core (50) with a simple configuration.

  The current measurement system (2) of the fourth aspect further includes a zero-cross detector (103) that detects a zero-cross of the voltage generated across the burden resistance switch (40) in the third aspect. In the degaussing mode, the control unit (112) turns on the burden resistance switch (40) when the magnetic flux density generated in the core (50) becomes zero based on the detection result of the zero cross detection unit (103).

  According to this configuration, when the magnetic flux density in the core (50) becomes zero, the burden resistance switch (40) is turned on. Therefore, the residual magnetic flux density of the core (50) is reduced to reduce the core (50). It becomes possible to demagnetize.

  In the current measurement system (2) of the fifth aspect, in the second aspect, the resistance adjustment unit (4) includes a first resistance (411) having an electric resistance value larger than that of the burden resistance (101). In the demagnetization mode, the control unit (112) disconnects the burden resistor (101) from the first and second ends (901, 902) in the secondary circuit (90) and the first and second ends (901, 902). ) Between the first resistor (411). The control unit (112) then disconnects the first resistor (411) from between the first and second ends (901, 902) and places a burden resistance (101) between the first and second ends (901, 902). Connecting.

  According to this configuration, even if the core (50) is magnetized, it is possible to demagnetize the core (50) by reducing the residual magnetic flux density of the core (50).

  In the current measurement system (2) of the sixth aspect, in the third aspect, the resistance adjusting unit (4) includes a plurality of resistance units (410, 420) each including a series circuit of a resistor and a switch. Each of the plurality of resistance units (410, 420) is connected in parallel to a series circuit of a burden resistance (101) and a burden resistance switch (40). The plurality of resistance units (410, 420) include a first resistance unit (410) and a second resistance unit (420). The first resistance unit (410) includes a series circuit of a first resistance (411) and a first switch (412). The first resistance (411) has a larger electrical resistance value than the burden resistance (101). The second resistance unit (420) includes a series circuit of a second resistance (421) and a second switch (422). The second resistance (421) has a larger electrical resistance value than the first resistance (411). In the demagnetization mode, the controller (112) turns off the burden resistance switch (40), turns off the first switch (412), and turns on the second switch (422), and then turns off the burden resistance switch (40). The first switch (412) is turned on and the second switch (422) is turned off. The control unit (112) overlaps a part of the period for keeping the second switch (422) on and a part of the period for keeping the first switch (412) on.

  According to this configuration, when the resistance between the first and second ends (901, 902) is switched from the second resistance (421) to the first resistance (411), the first and second ends (901, 902). ) Can be prevented from being opened.

  In any one of the second to sixth aspects, the current measurement system (2) of the seventh aspect further includes an operation unit (111) that receives an operation of the operator. The control unit (112) switches from the normal mode to the demagnetization mode in response to an operation on the operation unit (111).

  According to this configuration, it is possible to demagnetize the core (50) at an arbitrary timing.

  The current measurement system (2) according to the eighth aspect further includes a determination unit (113) that determines whether or not the magnitude of the primary current exceeds a predetermined threshold in any one of the second to seventh aspects. . When the determination unit (113) determines that the primary current has exceeded the threshold, the control unit (112) switches from the normal mode to the demagnetization mode.

  According to this configuration, when the core (50) is magnetized, the determination unit (113) determines that the core (50) has been magnetized, and the core (50) can be demagnetized.

  In the current measurement system (2) of the ninth aspect, in any one of the first to eighth aspects, the burden resistance (101) includes a variable resistance (43). The resistance adjuster (4) includes a variable resistor (43).

  According to this configuration, the residual magnetic flux density of the core (50) is changed by changing the electrical resistance value between the first and second ends (901, 902) of the secondary circuit (90) by the variable resistor (43). It is possible to demagnetize the core (50) by reducing the above.

  A distribution board (1) according to a tenth aspect includes a current measurement system (2) according to any one of the first to ninth aspects, a conductive member (conductive bar 84), and at least a conductive member (conductive bar 84). A storage cabinet (70).

  According to this configuration, even when the core (50) is magnetized, the residual magnetic flux density of the core (50) is reduced by the primary current passing through the through hole (500) of the core (50), and the core (50 ) Can be demagnetized. Further, when the measuring unit 102 measures the secondary current, it is not affected by other resistance elements.

DESCRIPTION OF SYMBOLS 1 Distribution board 2 Current measurement system 4 Resistance adjustment part 40 Burden resistance switch 410 1st resistance unit 411 1st resistance 412 1st switch 420 2nd resistance unit 421 2nd resistance 422 2nd switch 43 Variable resistance 50 Core 500 Through-hole 60 Coil 84 Conductive bar (conductive member)
90 Secondary side circuit 901 1st end 902 2nd end 101 Burden resistance 102 Measuring part 103 Zero cross detection part 111 Operation part 112 Control part

Claims (10)

A core having a through hole for passing a conductive member through which an alternating primary current flows;
A coil wound around the core;
A secondary circuit including a load resistor, having first and second ends, wherein the first and second ends are respectively connected to both ends of the coil without other resistance elements;
A measurement unit for measuring the primary current based on a detection voltage generated between both ends of the burden resistor;
With
In the secondary side circuit, the burden resistance is connected between the first and second ends without being connected in series with another resistance element,
The secondary circuit includes a resistance adjustment unit that changes an electric resistance value between the first and second ends in the secondary circuit. Current measurement system. A control unit for controlling the resistance adjusting unit;
The controller is
A normal mode for maintaining the electrical resistance value between the first and second ends in the secondary circuit at a predetermined value;
A demagnetization mode in which the electrical resistance value between the first and second ends in the secondary side circuit is increased from the predetermined value and then returned to the predetermined value;
The current measurement system according to claim 1. The resistance adjusting unit includes a burden resistance switch connected in series with the burden resistance between the first and second ends,
The controller is
In the normal mode, the burden resistance switch is kept on,
The current measurement system according to claim 2, wherein in the demagnetization mode, the burden resistance switch is turned off and then turned on. A zero-cross detector that detects a zero-cross of a voltage generated between both ends of the burden resistance switch;
The current measurement system according to claim 3, wherein the control unit turns on the burden resistance switch when a magnetic flux density generated in the core becomes zero based on a detection result of the zero-cross detection unit in the demagnetization mode. The resistance adjuster includes a first resistor having a larger electrical resistance value than the burden resistance,
In the demagnetization mode, the control unit disconnects the burden resistance from between the first and second ends in the secondary circuit and connects the first resistance between the first and second ends, and then The current measurement system according to claim 2, wherein the first resistor is disconnected from between the first and second ends, and the burden resistor is connected between the first and second ends. The resistance adjusting unit includes a plurality of resistance units each including a series circuit of a resistor and a switch,
Each of the plurality of resistance units is connected in parallel to a series circuit of the burden resistance and the burden resistance switch,
The plurality of resistance units are:
A first resistance unit comprising a series circuit of a first resistor and a first switch having a larger electrical resistance value than the burden resistance;
A second resistor unit comprising a series circuit of a second resistor and a second switch having a larger electrical resistance value than the first resistor;
Including
In the degaussing mode, the control unit turns off the burden resistance switch, turns off the first switch, and turns on the second switch, and then turns off the burden resistance switch, turns on the first switch, and Turn off the second switch,
The current measurement system according to claim 3, wherein the control unit overlaps a part of a period for keeping the second switch on and a part of a period for keeping the first switch on. It further includes an operation unit that receives an operation of the operator
The current measurement system according to any one of claims 2 to 6, wherein the control unit switches from the normal mode to the degaussing mode in accordance with an operation on the operation unit. A determination unit for determining whether the magnitude of the primary current exceeds a predetermined threshold;
The current measurement system according to claim 2, wherein the control unit switches from the normal mode to the demagnetization mode when the determination unit determines that the primary current has exceeded the threshold value. The burden resistance comprises a variable resistance,
The current measurement system according to claim 1, wherein the resistance adjustment unit includes the variable resistance. The current measurement system according to any one of claims 1 to 9,
The conductive member;
A cabinet that houses at least the conductive member;
Distribution board equipped with.

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