JPS5837686B2 - Current transformer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current transformer, and more particularly to a current transformer that can be used for both alternating current and direct current, and has good transient characteristics, temperature characteristics, and measurement accuracy.

Conventional current transformers that have been used include wound type current transformers and Hall element type current transformers.

In the former type of wound type current transformer, a secondary winding is wound around an annular core through which a primary conductor passes, and both ends of the winding are connected through a detection resistor. The current flowing through the primary conductor is measured by measuring the voltage, but the major drawback of this current transformer is that it cannot measure the direct current component, as is well known.

In the latter Hall element type current transformer, a part of the annular core through which the primary conductor passes is cut out to form a C-shaped core with a gap in a part of the magnetic path. By arranging a Hall element inside the C-shaped core, the change in magnetic flux generated in the C-shaped iron core by the primary conductor is directly converted into a change in voltage by this Hall element, which is further amplified by an amplifier and the value measured. , which measures the current flowing through the primary conductor.

According to this current transformer, both the DC component and the AC component can be measured as the current flowing through the primary conductor.

However, even if the current is constant, if the ambient temperature around the Hall element changes, the output voltage of the Hall element will fluctuate many times, and accordingly, the output voltage of the amplifier will also fluctuate several times.

In other words, Hall element type current transformers not only cause large measurement errors due to the influence of ambient temperature, etc., but also have the disadvantage that because the magnetic flux in the iron core is not canceled, the iron core is easily saturated, which also causes large measurement errors. There is.

Further, a feedback current type Hall current transformer as shown in FIG. 1 is also known.

This current transformer is an improved version of the Hall element type current transformer described above, and changes in the magnetic flux φ1 generated in the C-shaped core 2 due to the current flowing through the primary conductor 1 are arranged in the air gap 3 of the C-shaped core 2. directly converted into a change in voltage by the Hall element 4,
This is input to the feedback amplifier 5, and its output current ■2 is passed through the secondary winding 6 to create a magnetic flux φ2 in a direction that cancels the magnetic flux φ1 generated by the primary conductor 1, and these magnetic fluxes φ1 and φ2
In a state where the output voltage vh of the Hall element 4 is equal, that is, in a balanced state where the output voltage vh of the Hall element 4 is zero, the output current of the feedback amplifier 5, that is, the output current I2 of the secondary winding 6, is connected in series to the secondary winding 6. By measuring the voltage V2 across the detection resistor 70, the current (2) flowing through the primary conductor 1 is measured.

In the case of this current transformer, the Hall element 4 is used to detect when the magnetic flux (φ1 - φ2) applied to the Hall element 4 becomes zero, so the output of the Hall element directly corresponds to the measured value. Compared to the above-mentioned Hall element type current transformer, the current transformer has extremely high accuracy, and some with a measurement accuracy of about 0.3% have been manufactured.

However, in this feedback current type Hall current transformer, when the current 1 flowing through the primary conductor changes rapidly, the feedback amplifier 5
Since there is a limit to the response speed of the sensor, it cannot respond to changes in the current in the primary conductor, resulting in a large measurement error.

Furthermore, a current transformer as shown in FIG. 2, which is a combination of the above-mentioned wound type current transformer and Hall element type current transformer, is also known.

In FIG. 2, the same reference numerals as those in FIG. 1 indicate the same or equivalent components, 8 is an amplifier that amplifies the output voltage of the Hall element 4, and 9 is the voltage V2 across the output voltage detection resistor 70 of this amplifier 8. It is an adder that adds.

This current transformer is suitable as a current transformer for AC power systems, etc. where the current flowing through the primary conductor 1 has a small DC component.
When the direct current component of the current I1 in the secondary conductor 1 approaches 100%, there is a drawback of the Hall element type current transformer described above, namely that measurement errors become large due to changes in ambient temperature and saturation of the iron core.

The purpose of the present invention is to eliminate the drawbacks of the prior art described above, and provide a high-precision current transformer that can detect both DC and AC components, has little fluctuation due to the influence of ambient temperature, etc., and has a fast response speed. There is something to do.

To achieve this purpose, the present invention has been developed as mentioned above. In a return current type Hall current transformer, a tertiary winding is further wound around the core and element, and the output of this tertiary winding is added to the output of the feedback amplifier to detect the current flowing through the primary conductor. It is characterized by

Hereinafter, the present invention will be explained in detail with reference to the illustrated embodiments.

FIG. 3 is a perspective view of a current transformer according to an embodiment of the present invention.

An iron core 2 having one or more (one in this figure) voids 3 is provided so as to surround the primary conductor 10, and the voids 3
Inside, a Hall element 4 is arranged so as to be orthogonal to the magnetic flux φ1 generated in the magnetic path of the iron core 2 by the primary conductor 1.

Further, a secondary winding 6 and a tertiary winding 10 are wound around the iron core 2 and the gap 3 by the same number of turns so as to interlink with the iron core 2 and the gap 3.

The output voltage vh of the Hall element 4 is input to the feedback amplifier 5, and the feedback amplifier 5 is connected to the secondary winding 6 so that its output current I2 flows through the secondary winding 6 and the detection resistor 7.

Both ends of the tertiary winding 100 are short-circuited by a detection resistor 11,
The output voltage (3) of the detection resistor 11 is added to the output voltage (2) of the detection resistor 7 by an adder 9, and the output of the adder 9 is added to the load resistor 12.

Now, when a direct current flows as the current I1 in the primary conductor 1, the magnetic flux φ generated in the iron core 2 by the current I1
is also a direct current, and the tertiary winding 10 is short-circuited by the detection resistor 11.
Since no voltage is induced in the tertiary winding 100 current I3
becomes zero, and the voltage v3 of the detection resistor 11 is zero.

On the other hand, this magnetic flux φ1 is detected by the Hall element 4,
When the output voltage vh is applied to the input of the feedback amplifier 50, the output current 2 of the feedback amplifier flows to the secondary winding 6.

This current I2 is the magnetic flux φ generated by this current ■2
2 flows in a direction to cancel the magnetic flux φ1, the magnetic fluxes φ1 and φ2 become equal, and the output voltage vh of the Hall element 4 increases until it becomes zero, and is balanced at zero.

Therefore, in this equilibrium state, the current ■2 is the current I,
By measuring the current I1, it is possible to measure the current I1 flowing through the primary conductor.

The current (2) is measured by measuring the voltage (2) across the detection resistor 70 connected in series to the secondary winding 6.

Therefore, of the adder 90 input voltages V2 and 3, the voltage
3 is zero, and the output voltage V out of the adder 9 is a voltage? 2
is equal to the output voltage Vout or output current I
out is exactly proportional to the current ■1 flowing through the primary conductor 1.

By the way, since the secondary winding 6, which is an inductive load, is connected as the load of the feedback amplifier 5, if the current I1 flowing through the primary conductor 1 suddenly changes, L.

ga. line. i7p-ppy). Current feedback by the feedback amplifier 5, which merely follows the dt effect, becomes difficult.

That is, in a region where the frequency of the current (1) flowing through the primary conductor 1 is sufficiently high, the current (2) is zero, and the voltage (2) across the detection resistor 70 is also zero. An induced voltage is generated by the time change dot of the magnetic flux φ1 in the iron core 2, and by short-circuiting this with the detection resistor 11, the tertiary winding 1
A current I3 flows in the iron core 2, and the magnetic flux φ3 generated in the iron core 2 due to the current I3 cancels the magnetic flux φ1 and is balanced.

Therefore, electrician. is exactly proportional to the current ■1, and by measuring this current ■3, the primary current I1
can be measured.

This current (3) is measured by measuring the voltage v3 across the detection resistor 110 connected across the tertiary winding 100.

Therefore, of the input voltages v2 and 3 of the adder 90, the voltage V2 is zero, and the output voltage Vout of the adder 9 is the voltage v3.
The output voltage Vout or the output current Iout is exactly proportional to the current flowing through the primary conductor 1.

Furthermore, when the current ■1 flowing through the primary conductor 1 is a current in a low frequency region to which both the feedback amplifier 5 and the tertiary winding 10 respond, the current I3 flows through the tertiary winding 10 according to 4φ1. However, the magnetic flux φ3 generated in the iron core 2 by this current dt13 has a low frequency and a low induced voltage, so it does not flow enough to make (φ1-φ3) zero.

Therefore, a Hall voltage vh is generated in the Hall element 4 according to (φ1φ3), and the feedback amplifier 5 causes the secondary winding 6 to generate a current
2 is applied, and the Hall voltage vh is zero, that is, {φ1(φ2
+φ3)} becomes zero.

Therefore, currents ■2 and ■3 are taken out as voltages v2 and v3 across detection resistors 7 and 11, and their output voltage v2
The output voltage Vout? which is the sum of and ■3 by the adder 9. ■2+
V3 or the output current Iout is exactly proportional to the current ■1 flowing through the primary conductor 1.

As described above, according to the current transformer of this embodiment, the current flowing through the primary conductor 1 can be measured with very high accuracy, with a measurement error of 0.3 factor or less, from direct current to high frequency ranges of several tens of KHz or more. can be measured.

This is because the Hall element 4 is used only to detect zero magnetic flux for direct current, so it is not affected by the temperature characteristics and nonlinear errors peculiar to the Hall element 4, and also for high frequency alternating current. Not only can highly accurate measurements be made using the principle of a wound current transformer, but also the residual magnetic flux (φ1 - φ3) in the iron core 2, which causes errors, can be measured in the region between direct current and high frequency. This is because the Hall element 4 detects this and the feedback amplifier 5 cancels it, so in principle the measurement has zero error.

Furthermore, according to the current transformer of this embodiment, the following effects can also be obtained.

In order to detect low frequencies up to complete direct current using the above-mentioned wound type current transformer, it is necessary to increase the cross-sectional area of the iron core to infinity, which is virtually impossible.

That is, when compared at the same frequency, the current transformer of this embodiment has a much smaller iron core than a wound type current transformer.

Furthermore, in order to detect a high frequency current using the feedback current type Hall current transformer shown in FIG. This output voltage is
It is impossible to exceed the power supply voltage of the feedback amplifier 5, dI, and a high frequency current dt where L exceeds the power supply voltage of the feedback amplifier 5 cannot be detected.

Even if this L column dt does not exceed the power supply voltage of the feedback amplifier 5, as the frequency increases, the output required of the feedback amplifier 5 increases, and the output of the feedback amplifier 5 is limited due to thermal or high frequency. Therefore, there is a limit to the ability to detect high frequency current.

In contrast, in the current transformer of this embodiment, the high-frequency current is not detected by the secondary winding 6 connected to the feedback amplifier 5, but by the separately wound tertiary winding 10. Therefore, the aforementioned limitations due to the use of the feedback amplifier 5 do not occur.

In the embodiment shown in FIG. 3, the Hall element 4 was used as the element for detecting DC magnetic flux, but this is not limited to a Hall element, and any device that can detect a DC magnetic field or DC magnetic flux may be used. For example, it is also possible to use a magnetic diode, a magnetoresistive element, etc.

Also, the adder 9 is an analog quantity adder, but the voltage
It is also possible to convert 2 and 3 into digital amounts using an analog-to-digital converter and add them using a digital adder.

Further, the number of turns of the secondary winding 6 and the number of turns of the tertiary winding 100 do not necessarily have to be the same.

However, if they do not match, the addition constant (K
It is necessary to vary K2 and K3 in 2v2+K3 (3) depending on the number of turns of each winding, but this can be easily done with a conventional analog adder.

In addition, for the iron core 2, considering the delay of the magnetic flux φ1 due to eddy current, a metal material such as a silicon steel plate is suitable for low frequencies, and a powder material such as ferrite is suitable for high frequencies.

FIG. 4 shows a current transformer according to another embodiment of the present invention, and in the figure, the same reference numerals as in FIG. 3 indicate the same or equivalent parts.

In this embodiment, the number of turns of the secondary winding 6 and the tertiary winding 100 are the same, the detection resistors 7 and 10 and the adder 9 shown in FIG. 3 are omitted, and the secondary winding is connected to the load resistor 12. 6, the output currents 2 and I3 of the tertiary winding 10 are made to flow simultaneously.

Therefore, compared to the embodiment shown in FIG. 3, the structure can be significantly simplified.

Moreover, FIG. 5 shows a current transformer according to still another embodiment of the present invention, and the same reference numerals as in FIG. 3 indicate the same or equivalent parts.

In this embodiment, the output current of the secondary winding 6 and the tertiary winding 10 is
A current transformer 13 is used as a means for adding and detecting 2 and 3.

Since the secondary winding 6, the tertiary winding 10, and the current transformer 13 are insulated from each other, they have the advantage of being less susceptible to electrostatic noise and the like.

In this embodiment, the number of turns of the secondary winding 6 and the tertiary winding 10 with respect to the iron core 2 is determined when the current transformer 13 detects the currents 2 and 3. Current transformer 1 of next winding 10
The number of turns relative to 3 can be adjusted, so they do not have to be the same.

As explained below, according to the present invention, from direct current to several tens of
It is possible to perform highly accurate detection up to the relatively high frequency range of KHz, and since the residual magnetic flux is canceled by the feedback amplifier, there is no saturation of the iron core, the cross-sectional area of the iron core can be made small, and the equipment can be made smaller. It is also possible to reduce the burden on the feedback amplifier.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing a conventional feedback current type Hall current transformer.
FIG. 2 is a perspective view showing a conventional current transformer that combines a wound wire current transformer and a Hall element type current transformer, and FIG. 3 is a perspective view showing a current transformer according to an embodiment of the present invention. 4 and 5 are perspective views showing current transformers according to other embodiments of the present invention. 1...Primary conductor, 2...Iron core, 3...Gap, 4...
...Hall element, 5...Feedback amplifier, 6...Secondary winding, 7, 11...Detection resistor, 9...Adder, 10...
...Tertiary winding, 12...Load resistance, 13...Current transformer.

Claims (1)

[Claims] 1. An iron core through which an l-order conductor passes through and has a gap in a part of the magnetic path, and an element that generates an induced voltage when magnetic flux is applied, which is placed in the gap of the iron core. , a current transformer comprising a feedback amplifier that converts an induced voltage generated in the element into a current, and a secondary winding wound around the iron core and the element and through which the output current of the feedback amplifier flows. A current transformer characterized in that a tertiary winding is wound around the element, and the output of the tertiary winding is added to the output of the feedback amplifier. 2. In claim 1, the output of the feedback amplifier is extracted as a voltage by a first detection resistor connected to the secondary winding, and the output of the tertiary winding is output to the tertiary winding. A current transformer characterized in that a voltage is extracted by a connected second detection resistor and the two output voltages are added by an adder. 3. The current transformer according to claim 2, wherein the first and second detection resistors are shared by one resistor, and the adder is omitted. 4. In claim 1, the output of the feedback amplifier is extracted as a current by a current transformer that detects the output current of the secondary winding, and the output of the tertiary winding is the output of the tertiary winding. A current transformer characterized in that the current is extracted as a current by a current transformer that detects the current.