JPH09304441A - Current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain overvoltage, increase of error and waveform distortion which are caused by higher harmonic currents contained in a primary current, by installing a bandpass filter(BPF) which cuts off frequencies except a measuring frequency, in the output circuit of the secondary winding of an air-core current transformer. SOLUTION: An overvoltage limiting circuit 6, a voltage follower circuit 7, a BPF 8, a voltage amplifier 9 and a phase shifting circuit 10 are connected with the secondary winding output circuit of an air-core current transformer of a current detecting part 5. The circuit 6 consists of resistors and capacitors, and restrains an overvoltage due to higher harmonic currents contained in a voltage to be measured. The circuit 7 prevents the BPF from being affected by inductance and wiring resistance of the current detecting part 5, and resistors and capacitors of the circuit 6. The BPF 8 is used as the countermeasure for higher harmonic currents due to the air-core current transformer, and cuts off frequency components except the frequency to be measured. The gain is changed and adjusted by the voltage amplifier 9. The phase is changed and adjusted by the phase shifting circuit 10. Thereby a voltage having an arbitrary phase to an input voltage is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention does not have a winding core of a non-magnetic material formed in an annular or rectangular shape and a secondary winding wound evenly along the magnetic path of the winding core, or without a winding core. An air-core transformer that consists of a secondary winding that is evenly wound along the magnetic path formed by the measured current, is magnetically coupled to the primary conductor through which the measured current flows, and transforms the measured current into a voltage for detection. The present invention relates to a current detector, and more particularly, to a current detector in which error adjustment of an air-core current transformer can be easily performed.

[0002]

2. Description of the Related Art Generally, a current transformer (hereinafter, referred to as an air-core current transformer) that transforms a current to be measured into a voltage and detects the voltage has been widely used. FIG. 5: is a block diagram which shows an example of the conventional air-core current transformer of this kind.

As shown in FIG. 5, an air-core current transformer is a secondary winding in which a winding core 1 made of a non-magnetic material formed in an annular or rectangular shape and a magnetic path 3 of the winding core 1 are evenly wound. The wire 2 or the secondary winding 2 which is wound uniformly along the magnetic path 3 formed by the current to be measured without having the winding core 1 is magnetically coupled to the primary conductor through which the current to be measured flows. The measured current is converted into voltage and detected.

In FIG. 5, reference numeral 4 is a through window of the air-core current transformer. Now, in such an air-core current transformer, the output voltage E of the secondary winding 2 thereof is generally expressed by the following equation (1).

[0005]

[Equation 1]

Where k: coefficient N: number of turns of the secondary winding 2 (turns) S: effective area (m ² ) μ ₀ : vacuum permeability I ₁ : primary current (A) f: primary current Frequency (Hz) r: Average magnetic path radius (m) In such an air-core current transformer, the effective sectional area S and the average magnetic path radius r in the above formula (1) are the dimensional accuracy of the winding core 1 and the secondary A difference from the design value appears depending on the winding state of the winding wire 2 and the like.

Since these differences affect the output voltage of the air-core current transformer and cause errors, they cannot be ignored when the air-core current transformer is required to have strict accuracy.

Further, as is clear from the above equation (1),
Since the output voltage E of the secondary winding 2 is proportional to the frequency f of the primary current, when the primary current contains a harmonic current, the harmonic current component is amplified by a frequency double and the secondary current is increased. It becomes the output voltage of the winding 2, and causes overvoltage, error, and waveform distortion.

Generally, the output voltage E of the secondary winding 2 of the air-core current transformer is adjusted by adjusting the number of turns N of the secondary winding 2. On the other hand, in the air-core current transformer, in order to mitigate the influence of the external magnetic field, the secondary winding 2 is wound so as to be uniformly distributed around the entire circumference of the magnetic path 3.

Therefore, when the number of turns N of the secondary winding 2 is adjusted in order to keep the error of the air-core current transformer within the specified range, simply by rewinding or adding more turns, the magnetic path It becomes impossible to evenly arrange the secondary windings 2 over the entire circumference of 3.

For this reason, for example, it is necessary to remove the once wound secondary winding 2 and rewind it so that the secondary winding 2 has an evenly distributed winding. Also, when an air-core current transformer is installed in the field, etc., if an error occurs due to the influence of the external magnetic field, the configuration of the primary conductor, the adjacent magnetic material, etc., the secondary winding for the purpose of adjusting this error It may be necessary to adjust the number of turns N of the wire 2. In such a case, in order to remove the air-core current transformer from the mounting structure and rewind the secondary winding 2, complicated work such as disassembling the mounting structure is involved.

[0012]

As described above, in the conventional air-core current transformer, generally, when the error is out of the specified range in the error test after fabrication, the number of turns of the secondary winding is adjusted. In this case, in order to ensure that the secondary winding has a uniform distribution winding around the entire circumference of the magnetic path, the secondary winding that has been wound once is removed, and the secondary winding is rewound. It is necessary to go back to work.

Further, the air-core current transformer may require error adjustment after it is installed on site, but in this case, complicated work such as disassembling the mounting structure of the air-core current transformer is involved, which is not practical. It becomes a problem.

Further, although the ratio error can be adjusted by adjusting the number of turns of the secondary winding, the phase angle error cannot be adjusted, and the output voltage of the secondary winding is equal to the frequency of the primary current. Since they are proportional to each other, there is a problem that harmonics included in the primary current cause overvoltage, increase in error, waveform distortion, and the like.

An object of the present invention is to adjust the error of the air-core current transformer without adjusting the number of turns of the secondary winding, without complicated work on site, without degrading the performance of the air-core current transformer. An object is to provide a current detector that can be easily adjusted.

Another object of the present invention is to provide a current detector capable of easily suppressing an overvoltage, an increase in error, and a waveform distortion due to a harmonic current contained in a primary current.

[0017]

In order to achieve the above object, a winding core of a non-magnetic material formed in an annular or rectangular shape and a secondary winding wound evenly along a magnetic path of the winding core. ,
Alternatively, it consists of a secondary winding that has no winding core and is wound evenly along the magnetic path formed by the measured current, and is magnetically coupled to the primary conductor through which the measured current flows, transforming the measured current into a voltage. In the air-core current transformer to be detected as described above, first, in the invention corresponding to claim 1, the output circuit of the secondary winding of the air-core current transformer has a band for cutting frequency components other than the frequency of the current to be measured. It comprises a pass filter.

Therefore, in the current detector of the invention according to claim 1, in the output circuit of the secondary winding of the air-core current transformer,
By providing the band pass filter, it is possible to detect only the frequency component of the current to be measured without causing waveform distortion.

Further, in the invention corresponding to claim 2, in the output circuit of the secondary winding of the air-core current transformer, the output voltage of an arbitrary amplitude is output without changing the phase of the input voltage by variably adjusting the gain. The output voltage amplifier is provided.

Therefore, in the current detector of the invention according to claim 2, in the output circuit of the secondary winding of the air-core current transformer,
Since the output voltage of the secondary winding can be adjusted by adjusting the gain by providing the voltage amplifier, it is easy to set the optimum gain without adjusting the number of turns of the secondary winding. The ratio error can be adjusted to a minimum.

Further, in the invention corresponding to claim 3, the output circuit of the secondary winding of the air-core current transformer outputs the voltage as an arbitrary phase voltage without changing the amplitude of the input voltage by variably adjusting the phase. It comprises a phase shift circuit.

Therefore, in the current detector of the invention according to claim 3, in the output circuit of the secondary winding of the air-core current transformer,
By providing the phase shift circuit, the circuit constant is optimally set, and thus it is possible to easily adjust the phase angle error that cannot be performed by adjusting the number of turns of the secondary winding.

On the other hand, in the invention according to claim 4, the output circuit of the secondary winding of the air-core current transformer is provided with an overvoltage suppressing circuit including a resistor and a capacitor for suppressing an overvoltage due to a harmonic current contained in the measured current. It is equipped with.

Therefore, in the current detector of the invention according to claim 4, in the output circuit of the secondary winding of the air-core current transformer,
By providing the overvoltage suppressing circuit, it is possible to suppress the overvoltage due to the harmonic current or resonance included in the measured current (primary current).

Further, in the invention according to claim 5, in the output circuit of the secondary winding of the air-core current transformer, a band pass filter for cutting frequency components other than the frequency of the current to be measured and a gain variable. A voltage amplifier that outputs an output voltage with an arbitrary amplitude without changing the phase of the input voltage by adjusting it, and a phase shifter that outputs a voltage with an arbitrary phase without changing the amplitude of the input voltage by adjusting the phase variably. A circuit and an overvoltage suppressing circuit including a resistor and a capacitor for suppressing an overvoltage due to a harmonic current included in the measured current.

Therefore, in the current detector of the invention according to claim 5, the output circuit of the secondary winding of the air-core current transformer,
By including a bandpass filter, a voltage amplifier, a phase shift circuit, and an overvoltage suppression circuit, it is possible to detect only the frequency component of the current to be measured without causing waveform distortion, and to adjust the gain. Since the output voltage of the secondary winding can be adjusted by this, the ratio error can be easily adjusted to the minimum without adjusting the number of turns of the secondary winding. It is possible to easily adjust the phase angle error, which could not be achieved by adjusting the number of times, and also to suppress the overvoltage due to the harmonic current and the resonance.

Further, in the invention corresponding to claim 6, in the current detector of the invention according to claim 4 or 5, the air-core current transformer is provided in the output circuit of the secondary winding of the air-core current transformer. It is configured by adding a voltage follower circuit that does not affect the inductance, winding resistance, resistance of the overvoltage suppression circuit, and capacitor.

Therefore, in the current detector of the invention according to claim 6, in the output circuit of the secondary winding of the air-core current transformer,
By providing the voltage follower circuit, the influence of the inductance of the air-core current transformer, the winding resistance, the resistance of the overvoltage suppressing circuit, and the capacitor can be prevented from affecting the bandpass filter.

Furthermore, in the invention according to claim 7, in the current detector of the invention according to claim 2, the output voltage of the secondary winding uniformly wound along the magnetic path is set to an arbitrary value. I am trying to.

Therefore, in the current detector of the invention according to claim 7, since the output voltage of the secondary winding can be adjusted by setting the output voltage of the secondary winding to an arbitrary value, the air-core current transformation It suffices that the output voltage of the secondary winding of the device is a voltage that is approximately equal to the design value.

As a result, when manufacturing the air-core current transformer, the number of turns of the secondary winding may be a roughly designated value, so that it is possible to focus on reducing the influence of the external magnetic field (uniform distribution winding, etc.). Become.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of the current detector according to the present embodiment. That is, as shown in FIG. 1, the current detector of the present embodiment has a winding core of a non-magnetic material formed in an annular or rectangular shape and a secondary winding wound evenly along the magnetic path of the winding core. , Or a secondary winding that has no winding core and is wound evenly along the magnetic path formed by the current to be measured, and is magnetically coupled to the primary conductor through which the current to be measured flows. An overvoltage suppressing circuit 6, a voltage follower circuit 7, a bandpass filter 8, a voltage amplifier 9, and a phase shift circuit 10 are provided in the output circuit of the secondary winding of the air-core current transformer, which is the current detection unit 5 that is detected by the transformation. , And are connected as shown.

In FIG. 1, the connection order of the voltage amplifier 9 and the phase shift circuit 10 can be replaced with each other. Here, the overvoltage suppressing circuit 6 is composed of a resistor and a capacitor, and suppresses the overvoltage due to the harmonic current contained in the measured current.

Further, the voltage follower circuit 7 prevents the influence of the inductance and winding resistance of the current detecting section (air core current transformer) 5 and the resistance and capacitor of the overvoltage suppressing circuit 6 from affecting the band pass filter 8. To do.

Further, the bandpass filter 8 cuts off frequency components other than the frequency of the current to be measured. That is, in the air-core current transformer, since it is transformed into a secondary voltage proportional to the frequency contained in the current to be measured, the bandpass filter 8 is particularly connected as a countermeasure against the harmonic current.

The voltage amplifier 9 variably adjusts the gain to output an output voltage having an arbitrary amplitude without changing the phase of the input voltage. Further, the phase shift circuit 10 variably adjusts the phase to output the voltage of an arbitrary phase with respect to the input voltage without changing the amplitude of the input voltage.

Next, in the current detector of the present embodiment configured as described above, the overvoltage suppressing circuit 6 is provided in the output circuit of the secondary winding of the current detecting section (air-core current transformer) 5. As a result, overvoltage due to harmonic current and resonance can be suppressed.

Further, since the output circuit of the secondary winding of the current detector (air-core current transformer) 5 is provided with the voltage follower circuit 7, the inductance of the current detector (air-core current transformer) 5 It is possible to prevent the band pass filter 8 from being affected by the winding resistance, the resistance of the overvoltage suppressing circuit 6, and the capacitor.

Further, since the output circuit of the secondary winding of the current detector (air core current transformer) 5 is provided with the bandpass filter 8, the frequency of the current to be measured without causing waveform distortion. Only the component can be detected.

Further, since the output circuit of the secondary winding of the current detector (air-core current transformer) 5 is provided with the voltage amplifier 9, the output voltage of the secondary winding can be adjusted by adjusting the gain. Therefore, by setting the optimum gain, it is possible to easily adjust the ratio error to the minimum without adjusting the number of turns of the secondary winding.

Further, the output circuit of the secondary winding of the current detector (air-core current transformer) 5 is provided with the phase shift circuit 10, so that the circuit constant is optimally set so that the secondary winding It is possible to easily adjust the phase angle error, which could not be achieved by adjusting the number of windings.

As described above, the current detector according to the present embodiment is provided with a winding core of a non-magnetic material formed in an annular shape or a rectangular shape, and a secondary winding wound evenly along the magnetic path of the winding core. Alternatively, it consists of a secondary winding that has no winding core and is wound evenly along the magnetic path formed by the measured current, and is magnetically coupled to the primary conductor through which the measured current flows, transforming the measured current into a voltage. And an overvoltage suppressing circuit 6 configured to include a resistor and a capacitor in an output circuit of the secondary winding of the air-core current transformer that is the current detecting unit 5 to detect the overvoltage by the harmonic current included in the measured current, and An attempt is made to measure with the voltage follower circuit 7 that prevents the influence of the inductance and winding resistance of the current detection unit (air-core current transformer) 5 and the resistance and capacitor of the overvoltage suppression circuit 6 from affecting the bandpass filter 8. Frequency other than current frequency Band-pass filter 8 to cut a minute
And a voltage amplifier 9 that outputs the output voltage as an output voltage having an arbitrary amplitude without changing the phase of the input voltage by variably adjusting the gain, and an input amplifier that does not change the amplitude of the input voltage by variably adjusting the phase. The phase shift circuit 10 that outputs a voltage having an arbitrary phase with respect to the voltage is sequentially connected.

Therefore, the following various effects can be obtained. (A) Since the overvoltage suppressing circuit 6 including the resistor and the capacitor is provided, it becomes possible to easily suppress the overvoltage due to the harmonic current or resonance included in the measured current (primary current).

(B) Since the voltage follower circuit 7 is provided, the influence of the inductance of the current detecting section (air-core current transformer) 5, the winding resistance, the resistance of the overvoltage suppressing circuit 6 and the capacitor is eliminated by the band pass filter 8. It is possible to prevent it from reaching.

(C) Since the band pass filter 8 is provided, it is possible to detect only the frequency component of the current to be measured without causing waveform distortion. (D) Since the voltage amplifier 9 is provided, the output voltage of the secondary winding can be adjusted by adjusting the gain.

That is, by setting the optimum gain, it is possible to easily adjust the ratio error to the minimum without adjusting the number of turns of the secondary winding. (E) Since the phase shift circuit 10 is provided, the current detection unit (air-core current transformer) 5 is set by setting the circuit constants to the optimum value.
It is possible to adjust the output voltage phase of, and it is possible to easily adjust the phase angle error which could not be achieved by adjusting the number of turns of the secondary winding.

(F) Since the output voltage of the secondary winding can be adjusted by the above (d), the output voltage of the secondary winding of the current detector (air core current transformer) 5 is a voltage substantially equal to the design value. That would be fine.

As a result, when manufacturing the air-core current transformer, the number of turns of the secondary winding may be a roughly designated value, so that it is possible to focus on reducing the influence of the external magnetic field (uniform distribution winding, etc.). Become.

[0049]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a circuit configuration diagram showing the current detector in this embodiment. In FIG. 2, the current detector of the present embodiment has an output circuit of the secondary winding of the current detection unit 5, an overvoltage suppressing circuit 6, a voltage follower circuit 7, a band pass filter 8, a voltage amplifier 9, and The phase shift circuit 10 and the phase shift circuit 10 are connected as shown in the figure.

As shown in FIG. 3 (a), the current detector 5 includes a winding core 1 made of a non-magnetic material and a secondary winding 2 wound evenly along a magnetic path 3 of the winding core 1, or A secondary winding 2 having no winding core 1 and uniformly wound along a magnetic path 3 of the measured current.
Is an air-core current transformer that is magnetically coupled to the primary conductor through which the measured current flows and transforms the measured current into a voltage.

In manufacturing this air-core current transformer, emphasis is placed on reducing the influence of an external magnetic field on the output voltage. That is, the secondary winding 2 is wound as evenly as possible over the magnetic path 3, and as shown in FIG. 3B, a winding structure that is non-inductive to the magnetic field passing through the through window 4 of the air-core current transformer. With respect to the output voltage, it suffices that a voltage having a value approximately close to the design value is output.

On the other hand, an overvoltage suppressing circuit 6 including a resistor R and a capacitor C is connected between the output terminals of the secondary winding 2 of the air-core current transformer. The overvoltage suppressing circuit 6 is connected to suppress an overvoltage due to a harmonic current included in the measured current (primary current) or an overvoltage due to resonance.

A voltage follower circuit 7 consisting of an operational amplifier OP ₁ is connected to the output side of the overvoltage suppressing circuit 6. The voltage follower circuit 7 is connected to prevent the influence of the inductance and winding resistance of the air-core current transformer, the resistance R of the overvoltage suppressing circuit 6 and the capacitor C from affecting the band pass filter 8.

Further, on the output side of the voltage follower circuit 7, an operational amplifier OP ₂ , a resistor R ₁ , a variable resistor R ₂ ,
A bandpass filter 8 including R ₃ and capacitors C ₁ and C ₂ is connected.

The bandpass filter 8 is connected to detect only the current frequency to be measured. For example, when a current having a frequency of 50 Hz is detected, the amplitude ratio between the input voltage and the output voltage of the bandpass filter 8 is about 1.3 (see FIG. 4) and the phase difference is about 180 degrees.

On the output side of the band pass filter 8,
A voltage amplifier 9 composed of an operational amplifier OP ₃ , a resistor R _4, and a variable resistor R ₅ is connected. The input / output characteristics of this voltage amplifier 9 are

[0057]

[Equation 2]

[0058] However, e _o: output voltage e _i of the voltage amplifier 9 input voltage R ₄ of the voltage amplifier 9, R _5: resistor for gain adjustment of the voltage amplifier 9, represented by a variable resistor.

Here, the input and output voltages of the voltage amplifier 9 have the same phase. The voltage amplifier 9 is connected to adjust the output voltage of the current detector to minimize the ratio error.

Further, on the output side of the voltage amplifier 9, an operational amplifier OP ₄ , resistors R ₆ and R ₇ , a variable resistor R ₈ , and
A phase shift circuit 10 including a capacitor C ₃ is connected. The input / output characteristics of this phase shift circuit 10 are

[0061]

(Equation 3)

Here, e _o : output voltage of phase shift circuit 10 e _i : input voltage of phase shift circuit 10 R ₈ , C ₃ : variable resistance of phase shift circuit 10, capacitor ω: angular frequency (= 2πf) Be done.

As can be seen from the equation (3), the magnitudes of the input and output voltages of the phase shift circuit 10 are equal, and only the phase difference is arbitrary depending on the values of the resistors R ₆ , R ₇ , R ₈ and the capacitor C _3. It is adjustable to.

Therefore, the phase shift circuit 10 is connected to minimize the phase angle error of the current detector.
Note that the connection order of the voltage amplifier 9 and the phase shift circuit 10 can be interchanged.

[0065]

As described above, the winding core made of a non-magnetic material formed in an annular or rectangular shape and the secondary winding wound evenly along the magnetic path of the winding core or having no winding core. An air-core transformer that consists of a secondary winding that is evenly wound along the magnetic path formed by the measured current, is magnetically coupled to the primary conductor through which the measured current flows, and transforms the measured current into a voltage for detection. According to the invention corresponding to claim 1, in the current transformer, the output circuit of the secondary winding of the air-core current transformer is provided with a bandpass filter for cutting frequency components other than the frequency of the current to be measured. Therefore, it is possible to provide a current detector capable of detecting only the frequency component of the current to be measured without causing waveform distortion.

According to a second aspect of the present invention,
Since the output circuit of the secondary winding of the air-core current transformer is equipped with a voltage amplifier that outputs an output voltage of arbitrary amplitude without changing the phase of the input voltage by adjusting the gain variably, the gain adjustment The output voltage of the secondary winding can be adjusted by setting the optimum gain so that the ratio error can be easily adjusted to the minimum without adjusting the number of turns of the secondary winding. A detector can be provided.

Further, according to the invention corresponding to claim 3, in the output circuit of the secondary winding of the air-core current transformer, by variably adjusting the phase, the voltage of an arbitrary phase can be maintained without changing the amplitude of the input voltage. Since it is equipped with a phase shift circuit that outputs as, it is possible to easily adjust the phase angle error, which could not be done by adjusting the number of turns of the secondary winding, by setting the circuit constant to the optimum value. Can be provided.

On the other hand, according to the invention corresponding to claim 4,
Since the output circuit of the secondary winding of the air-core current transformer is equipped with an overvoltage suppression circuit consisting of a resistor and a capacitor that suppresses overvoltage due to harmonic currents contained in the measured current, the measured current (primary current) It is possible to provide a current detector capable of suppressing the overcurrent due to the harmonic current and resonance contained in the current detector.

Further, according to the invention corresponding to claim 5,
In the output circuit of the secondary winding of the air-core current transformer, a band-pass filter that cuts frequency components other than the frequency of the current to be measured, and a variable gain can be adjusted to change the input voltage phase without changing it. A voltage amplifier that outputs an amplitude output voltage, a phase shift circuit that outputs a voltage of any phase without changing the amplitude of the input voltage by variably adjusting the phase, and an overvoltage due to the harmonic current included in the measured current. Since it is equipped with an overvoltage suppression circuit that consists of a resistor and a capacitor that suppresses
It is possible to detect only the frequency component of the current to be measured, and it is possible to adjust the output voltage of the secondary winding by adjusting the gain, making it easy to adjust the ratio without adjusting the number of turns of the secondary winding. The error can be adjusted to a minimum, the phase angle error that could not be achieved by adjusting the number of turns of the secondary winding can be easily adjusted, and the overvoltage due to harmonic current and resonance can be suppressed. A possible current detector can be provided.

Further, according to the invention corresponding to claim 6, in the current detector of the invention according to claim 4 or 5, the output circuit of the secondary winding of the air-core current transformer,
Since the voltage follower circuit that does not affect the inductance of the air-core current transformer, the winding resistance, the resistance of the overvoltage suppression circuit, and the capacitor is added, the inductance of the air-core current transformer, the winding resistance, and the like. It is possible to provide a current detector capable of preventing the effect of the resistance and the capacitor of the overvoltage suppressing circuit from affecting the bandpass filter.

Further, according to the invention corresponding to claim 7, in the current detector of the invention according to claim 2, the output voltage of the secondary winding uniformly wound along the magnetic path is set to an arbitrary value. Since it is set to a value, the number of turns of the secondary winding can be set to the approximate design specified value when manufacturing the air-core current transformer, and it is possible to focus on reducing the influence of the external magnetic field (uniform distribution winding, etc.). A possible current detector can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a current detector according to the present invention.

FIG. 2 is a circuit configuration diagram showing an embodiment of a current detector according to the present invention.

FIG. 3 is a structural diagram of an air-core current transformer used for a current detection unit in the current detector of the embodiment.

FIG. 4 is a diagram showing an example of frequency characteristics of a bandpass filter used in the current detector of the embodiment.

FIG. 5 is a configuration diagram showing an example of a conventional air-core current transformer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Core of non-magnetic material, 2 ... Secondary winding, 3 ... Magnetic path, 4 ... Through window, 5 ... Current detection part, 6 ... Overvoltage suppression circuit, 7 ... Voltage follower circuit, 8 ... Band pass filter, 9 ... Voltage amplifier, 10 ... Phase shift circuit.

Claims (7)

[Claims] 1. A winding core of a non-magnetic material formed in an annular or rectangular shape and a secondary winding wound evenly along a magnetic path of the winding core, or a measured current is formed without the winding core. In an air-core current transformer, which consists of a secondary winding wound evenly along a magnetic path, forms a magnetic coupling with a primary conductor through which a current to be measured flows, and detects the current to be measured by transforming it into a voltage, A current detector, characterized in that the output circuit of the secondary winding of the air-core current transformer comprises a bandpass filter for cutting frequency components other than the frequency of the current to be measured. 2. A winding core of a non-magnetic material formed in an annular or rectangular shape and a secondary winding uniformly wound along a magnetic path of the winding core, or a measured current is formed without the winding core. In an air-core current transformer, which consists of a secondary winding wound evenly along a magnetic path, forms a magnetic coupling with a primary conductor through which a current to be measured flows, and detects the current to be measured by transforming it into a voltage, The current is characterized in that the output circuit of the secondary winding of the air-core current transformer is equipped with a voltage amplifier that outputs as an output voltage of arbitrary amplitude without changing the phase of the input voltage by variably adjusting the gain. Detector. 3. A winding core of a non-magnetic material formed in an annular or rectangular shape and a secondary winding wound evenly along a magnetic path of the winding core, or a measured current is formed without the winding core. In an air-core current transformer, which consists of a secondary winding wound evenly along a magnetic path, forms a magnetic coupling with a primary conductor through which a current to be measured flows, and detects the current to be measured by transforming it into a voltage, The current is characterized in that the output circuit of the secondary winding of the air-core current transformer is equipped with a phase shift circuit that outputs the voltage as an arbitrary phase voltage without changing the amplitude of the input voltage by variably adjusting the phase. Detector. 4. A winding core of a non-magnetic material formed in an annular or rectangular shape and a secondary winding wound evenly along a magnetic path of the winding core, or a measured current is formed without the winding core. In an air-core current transformer, which consists of a secondary winding wound evenly along a magnetic path, forms a magnetic coupling with a primary conductor through which a current to be measured flows, and detects the current to be measured by transforming it into a voltage, A current detector characterized in that the output circuit of the secondary winding of the air-core current transformer is provided with an overvoltage suppressing circuit composed of a resistor and a capacitor for suppressing an overvoltage due to a harmonic current contained in the measured current. 5. A winding core of a non-magnetic material formed in an annular or rectangular shape and a secondary winding uniformly wound along a magnetic path of the winding core, or a measured current is formed without the winding core. In an air-core current transformer, which consists of a secondary winding wound evenly along a magnetic path, forms a magnetic coupling with a primary conductor through which a current to be measured flows, and detects the current to be measured by transforming it into a voltage, In the output circuit of the secondary winding of the air-core current transformer, a band-pass filter that cuts frequency components other than the frequency of the current to be measured, and a variable gain can be adjusted to change the input voltage phase without changing it. A voltage amplifier that outputs the output voltage of the amplitude, a phase shift circuit that outputs the voltage of an arbitrary phase without changing the amplitude of the input voltage by variably adjusting the phase, and an overvoltage caused by the harmonic current contained in the measured current. To suppress the resistance Current detector, characterized in that it comprises an, an overvoltage suppression circuit consisting of fine capacitor. 6. The current detector according to claim 4, wherein the output circuit of the secondary winding of the air-core current transformer includes an inductor, a winding resistance, and the winding resistance of the air-core current transformer. A current detector characterized in that a voltage follower circuit is added so as not to affect the resistance and the capacitor of the overvoltage suppressing circuit. 7. The current detector according to claim 2, wherein the output voltage of the secondary winding uniformly wound along the magnetic path is set to an arbitrary value. Detector.