JP2008002876A - Current sensor and electronic energy meter - Google Patents

Abstract

In a current sensor mainly for power measurement and power measurement, it is hardly affected by an external magnetic field, has excellent linearity and temperature characteristics, and is accurate even if it is a periodic current superimposed with a DC component. A current sensor capable of measuring the current is provided.
An annular magnetic collecting core divided into two substantially in the same shape is disposed opposite to each other with a gap, and a detection coil having the same size and number of turns is disposed in the gap portion. The detection coil was arranged by forming it as a coil pattern on the same substrate, and the magnetoresistances at the two gaps formed in the magnetic flux collecting core were made substantially the same.
In addition, for the magnetic resistance of the magnetic path through which the magnetic flux generated by the current to be measured flowing through the current bar penetrates, the ratio of the total magnetic resistance including the gap and the magnetic resistance inside the current collecting core is smaller than the output tolerance of the current sensor. Thus, the magnetic flux collecting core and the gap were configured.
[Selection] Figure 1

Description

The present invention provides means for accurately measuring an alternating current component of a current that is superimposed and periodically changed. In particular, the present invention relates to current measurement technology for power measurement and energy measurement in which measurement accuracy of AC components is important.

In general, current measurement in a circuit that handles high power requires insulation from the main circuit, and a separate current sensor is often used. As a typical current measurement method, a current transformer (current transformer; CT), a direct current sensor constituted by a magnetoelectric conversion element such as a Hall element, a Rogowski coil method, and the like are known.
The current sensor most commonly used in AC circuits is a current transformer (CT). This is a magnetic core with multiple secondary windings. When the current to be measured is changed by passing a current bar through the magnetic core, the resulting change in magnetic flux density in the core is offset. Thus, a current flows through the winding, and the current to be measured is measured by measuring the current in the secondary winding.

A configuration of a current measurement method for providing a gap in a magnetic core and detecting a magnetic flux generated in the magnetic core is shown, for example, in Prior Art Patent Document 1 and Prior Art Patent Document 2. In this case, the current to be measured is measured by arranging a magnetoelectric conversion element at the gap position of the magnetic flux collecting core with a gap and measuring the magnetic flux density generated in the magnetic flux collecting core by the current to be measured.
In addition, the Rogowski coil method is known as a method for mainly measuring a large current. In this configuration, as shown in Prior Art Patent Document 3, when a large number of air core coils are arranged in an annular shape and the current passing through the center thereof changes, the voltage generated by the change in magnetic flux passing through the air core coil Is obtained by integrating.

As in the Rogowski coil method, as a method using electromagnetic induction, a winding is provided around the gap collecting core, and the change in the magnetic flux in the collecting core due to the change in the measured current is detected by the winding coil. In some cases, it is used in a clamp-type current sensor or the like. FIG. 5 is a diagram showing a conventional configuration according to the present system. In FIG. 5, a magnetic flux collecting core 11 having a gap 12 surrounding the current bar 13 is disposed, and a detection coil 14 is wound around the magnetic flux collecting core 11. In this method, an output proportional to the time change of the magnetic flux density generated in the magnetic collecting core by the current to be measured is obtained from the detection coil 14. If this output is led to an integration circuit (not shown) and integration calculation is performed, a current to be measured can be obtained.
Japanese Patent Laid-Open No. 7-151793 JP 2003-43073 A Japanese Patent Laying-Open No. 2005-3589

With the progress of semiconductor technology, there is an increasing need for wattmeters and watt hour meters that can measure the power consumed by a current superimposed with a direct current such as a half-wave current. In general voltage and current composed of many frequency components including direct current, power is obtained by calculating a value of voltage × current for each frequency component. However, since the commercial AC power supply voltage does not include a DC component, the DC component of the current is not necessary for power measurement. On the other hand, the measurement accuracy of alternating current components directly affects the calculation accuracy of power.

However, the conventional current measurement method has the following problems.
First of all, an AC current can be measured with high accuracy in a current transformer, but when a current containing a DC component is passed through a current bar that passes through the current transformer, the DC component is not only measured. The AC component cannot be measured accurately due to the magnetic saturation of the core.
Current measurement by a DC current sensor using a magnetoelectric transducer can measure periodic current with the same degree of accuracy as measuring AC current that has no DC component, even if the DC component is superimposed. it can. However, since the output of this current sensor directly depends on the linearity and temperature characteristics of the magnetoelectric transducer in addition to the magnetic characteristics of the core, the AC measurement accuracy is generally inferior to that of the current transformer. In general, in addition to large variations in sensitivity of magnetoelectric transducers, variations in sensitivity as current sensors increase due to a relative positional shift between the magnetism collecting core and the magnetoelectric transducer.

Further, the Rogowski coil method has a manufacturing difficulty in that it is affected by an external magnetic field due to slight winding unevenness due to the air core.
Even in the case where electromagnetic induction is used as the detection principle, as in the Rogowski coil method, a coil wound around the magnetic collecting core causes a large error because the magnetic flux generated by the external magnetic field passes through the magnetic collecting core.

  FIG. 6 shows a path of magnetic flux in the magnetic flux collecting core when there is an external magnetic field. In FIG. 6, the magnetic flux collecting core 11 is an annular core having one gap 12, and a detection coil 14 is wound a plurality of times on the opposite side of the gap 12. When an external magnetic field enters from the lower side of FIG. 6, the magnetic flux is divided into the detection coil 14 side (φA) and the gap 12 side (φB) and passes through the core. When the magnetic flux φA on the detection coil 14 side fluctuates, an induced voltage is generated in the detection coil 14 and is superimposed on the generated voltage due to the current to be detected to cause an error. The magnetic resistance to the magnetic fluxes φA and φB is much smaller on the φA side without a gap, and therefore the magnetic flux φA penetrating the detection coil 14 is larger than φB. As a result, the current measurement error when there is an external magnetic field cannot be ignored. In order to avoid this external magnetic field, it was necessary to take measures such as surrounding the entire sensor with a magnetic shield.

  The present invention uses a current sensor that is not easily affected by an external magnetic field, has excellent linearity and temperature characteristics, and can accurately measure an alternating current component even with a periodic current superimposed with a direct current component, and the current sensor. An object is to provide an electronic watt-hour meter.

Therefore, in the present invention, the annular magnetic collecting cores divided into two substantially in the same shape are arranged to face each other with a gap, and a detection coil having the same size and number of turns is arranged in the gap portion, and the detection coil terminal Are connected in series so that their output voltages are added. In addition, the detection coil is arranged by forming it as a coil pattern on the same substrate, and the magnetic resistances at the two gaps formed in the magnetic flux collecting core are made substantially the same.

Furthermore, regarding the magnetic resistance of the magnetic path through which the magnetic flux generated by the current to be measured flowing through the current bar penetrates, the ratio of the total magnetic resistance including the gap and the magnetic resistance inside the current collecting core is smaller than the output tolerance of the current sensor. Thus, the magnetic flux collecting core and the gap were configured.
Furthermore, such a current sensor was used for an electronic watt-hour meter.

In the present invention, the annular magnetism collecting cores divided into two substantially in the same shape are arranged to face each other with a gap, and detection coils having the same size and number of turns are arranged in the gap portions at the two locations. Since the terminals are connected in series so that their output voltages are added, the detection voltage can be connected so that the voltage generated by the magnetic flux generated by the current to be measured is added, and the voltage generated by the magnetic flux generated by the external magnetic field is offset, The current detection error due to the external magnetic field can be extremely reduced.

  Further, since the detection coil is formed as a coil pattern on the same substrate, the dimensional accuracy in manufacturing is improved, and the variation in the voltage generated between the two detection coils can be reduced. The fact that the magnetic resistances at the two gaps formed in the magnetic collecting core are substantially the same means that when the magnetic flux due to the external magnetic field is split into two and passes through the gap, the amount of each magnetic flux can be made substantially the same. The effect of reducing the error voltage by subtracting the detection coil can be further improved.

  Furthermore, regarding the magnetic resistance of the magnetic path through which the magnetic flux generated by the current to be measured flowing through the current bar penetrates, the ratio of the total magnetic resistance including the gap and the magnetic resistance only inside the current collecting core is smaller than the output tolerance of the current sensor. Thus, since the magnetic flux collecting core and the gap are configured, even when an error occurs in the current measurement value as a result of the magnetic permeability of the magnetic flux collecting core material fluctuating due to magnetic saturation, the error can be kept below an allowable value.

  By using such a current sensor for an electronic wattmeter, an AC component can be detected with high accuracy even when the current includes a DC component.

Next, specific embodiments of the current sensor according to the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing a configuration of a current sensor according to the present invention. In FIG. 1, a first magnetic collecting core 1 and a second magnetic collecting core 2 made of a ferromagnetic material such as iron are disposed so as to face each other with a gap surrounding a current bar 3, and a substrate 6 is disposed in the gap. It is sandwiched. In the gap portion on the substrate 6, the first detection coil 4 and the second detection coil 5 having the same dimensions and the same number of turns are formed as a spiral coil pattern. After the first detection coil 4 and the second detection coil 5 are connected in series, their output terminals are led to the input terminal of the integrator 7.

  Next, the principle of current detection in the current sensor having the above configuration will be described. FIG. 2 is a diagram showing the flow of magnetic flux in the magnetic flux collecting core due to the current to be measured in the current sensor of the present invention. The current flowing in the current bar forms a magnetic field around its entire circumference, but most of the magnetic flux generated thereby circulates around the current collecting core that is placed around the current bar and made of a ferromagnetic material. When the current flowing through the current bar increases or decreases, the magnetic flux in the magnetic flux collecting core also increases or decreases correspondingly. In accordance with Faraday's law, an electromotive force proportional to the change in the magnetic flux is induced in the first detection coil 4 and the second detection coil 5 that are arranged so that the magnetic flux penetrates. The two detection coils are connected in series in the direction in which the induced electromotive force is added. If this output is guided to the integrator 7 and integration calculation is performed, a current to be measured can be obtained.

The winding direction of the first detection coil 4 and the second detection coil 5 can be either the same direction or the reverse direction. By connecting the coil terminals in series so that their output voltages are added, both exhibit the same performance.
On the other hand, in this type of current measurement, if there is a fluctuating external magnetic field, there is a problem that the induced electromotive force is superimposed on the output and the error is increased. FIG. 3 is a diagram showing the flow of magnetic flux when the external magnetic field 15 enters the current sensor of the present invention. In FIG. 3, the magnetic flux generated by the external magnetic field 15 enters from the lower part, and passes through the magnetic flux collecting core in two hands. In the present invention, since the magnetic resistances at the two gaps formed in the magnetic collecting core are substantially the same, the two separated magnetic fluxes φA and φB have substantially the same value, and the electromotive forces induced in the two detection coils. Is almost equal. Since the two detection coils are connected in series in the direction in which the magnetic flux generated by the current to be measured is added as shown in FIG. 2, with respect to the magnetic flux due to the external magnetic field in FIG. Since the electromotive force is offset, the effect of reducing the measurement error is exhibited.

  In a current sensor using a magnetic collecting core, current measurement errors occur due to the non-linearity of the magnetic properties of the magnetic collecting core material. In order to suppress this error to an allowable value or less, the magnetic flux collecting core and the gap are configured as follows in the present invention. FIG. 4 is a dimension diagram for calculating the magnetic resistance in the current sensor of the present invention, where the magnetic path length of the first and second magnetic flux collecting cores is li and the gap length is lg. The cross-sectional area of the magnetic path is the same S for all the magnetic paths, the magnetic permeability of the magnetic flux collecting core material is μi, and the magnetic permeability of air is μ0. In this magnetic circuit, the magnetic flux φ generated by the current I to be measured is given by the total magnetic resistance of the magnetic circuit as Rm.

It is represented by The total magnetic resistance Rm is the sum of the magnetic resistance Ri of the magnetic flux collecting core portion and the gap magnetic resistance Rg. Ri and Rg are calculated from the dimensions shown in FIG.

It is represented by The current measurement error is caused by a change in the magnetic resistance Ri of the magnetic flux collecting core portion by ΔRi due to the difference in the current to be measured and the ambient temperature. When calculating the relationship of the relative change Δφ / φ in the magnetic flux collecting core from “Equation 1”,

However, since the magnetoresistance change ΔRi of the magnetic flux collecting core is at most as high as Ri,

By setting the ratio Ri / Rm of the magnetic resistance Ri of the magnetic flux collecting core part to the total magnetic resistance Rm to be less than the allowable value, the measurement error of the current that is an output proportional to the magnetic flux in the magnetic flux collecting core can be reduced. It can be suppressed below the allowable value.
For example, if the relative magnetic permeability (magnification with respect to the air permeability) of the magnetic flux collecting core material is 1000 and the allowable error is 1%, then li / lg≈10, and the gap length lg is 2 mm, the magnetic path of the magnetic flux collecting core The length li can be allowed up to 20 mm.

The perspective view which shows the structure of the current sensor of this invention. The figure which shows the flow of the magnetic flux by the to-be-measured current in the current sensor of this invention The figure which shows the flow of the magnetic flux by the external magnetic field in the current sensor of this invention Dimensional diagram for magnetoresistance calculation in the current sensor of the present invention The perspective view which shows the structure of the current sensor by a prior art. The figure which shows the flow of the magnetic flux by the external magnetic field in the current sensor by the prior art

Explanation of symbols

1 First magnetic collecting core 2 Second magnetic collecting core 3 Current bar
4 First detection coil 5 Second detection coil 6 Substrate 7 Integrator 8 Cooling fin 9 Coil end 10 Rotating shaft
11 current collecting core 12 gap 13 current bar 14 detection coil 15 external magnetic field

Claims (5)

In a current sensor for detecting a measured current through a magnetic flux generated in a magnetic collecting core surrounding the current bar by a measured current flowing through the current bar, an annular magnetic collecting core divided into two substantially in the same shape has a gap. A current sensor comprising: a detection coil having the same size and number of turns disposed in the gap portion; and the detection coil terminals connected in series so that the output voltage is added. 2. The current sensor according to claim 1, wherein the detection coil disposed in the gap portion is formed as a coil pattern on the same substrate. 3. The current sensor according to claim 1, wherein the magnetic resistances of the gaps at two places formed between the magnetic collecting cores are substantially the same. 4. The current sensor according to claim 1, wherein the magnetic resistance of the magnetic path through which the magnetic flux generated by the current to be measured flowing through the current bar penetrates includes only the magnetic resistance inside the magnetic flux collecting core and the gap portion. 5. A current sensor comprising a magnetic flux collecting core and a gap so that a ratio of total magnetic resistance is smaller than an output tolerance of the current sensor. An electronic watt-hour meter that performs current measurement using the current sensor according to any one of claims 1 to 4.

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