JP2017203732A - Voltage measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage measurement device which can contactlessly measure the applied voltage of an electric power line with high accuracy.SOLUTION: The voltage measurement device comprises: a modulation circuit 4 for modulating a current flowing via the coupling capacitance of a core wire 1a of an electric power line 1 and a detection electrode 2 to a higher frequency than a voltage to be measured, by turning a switching element on and off; a drive circuit 8 of the switching element; a transformer 32, connected in series to the switching element, for generating a detection signal proportionate to a potential difference between the voltage to be measured and a reference potential; a demodulation circuit 4 for extracting a frequency component of the voltage to be measured from the detection signal; a post-stage amplification circuit 5; and a high voltage generation circuit 6 for generating a reference potential to reduce a current flowing in the primary winding of the transformer 32 on the basis of the output signal of the post-stage amplification circuit and applying it to the primary winding, the voltage to be measured being identified on the basis of the reference voltage when the potential difference drops to or below a prescribed value, the detection electrode 2 containing a metal thin-film 2a in an insulation member 2b and having flexibility sufficient for it to be wound around the outer circumference of the electric power line 1.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a voltage measuring apparatus that measures a voltage applied to a core of a power line using a detection electrode attached to the power line.

2. Description of the Related Art Conventionally, a voltage measuring apparatus that measures a voltage applied to a power line in a non-contact manner using a coupling capacitance between the core of the power line and an electrode in a detection probe is known.
In this type of voltage measuring apparatus, the coupling capacitance changes due to the positional relationship of the detection probe with respect to the power line, the material of the insulation coating of the power line, the difference in dielectric constant depending on the surrounding environment such as temperature and humidity, and this becomes a measurement error. Therefore, there is a case where the voltage of the power line cannot be measured with high accuracy.
For this reason, the prior art described in patent documents 1-3 is known as a voltage measuring device which solves the above-mentioned problem.

The voltage measuring device described in Patent Documents 1 and 2 includes a detection electrode, a variable capacitance circuit including a capacitance changing function body such as a diode and a capacitor, and a driving circuit thereof, a current detector, an amplifier circuit, a synchronous detection circuit, an integration circuit, A voltage generation circuit and the like are provided.
In these voltage measuring devices, the capacitance of the capacitance changing function body is changed, and the current flowing through the measurement target, for example, the coupling capacitance between the power line and the detection electrode, is changed according to the operating frequency of the capacitance changing function body. Has been. The current is converted into a voltage via a current detector, and a signal corresponding to the voltage of the power line is generated via a synchronous detection circuit, an amplifier circuit, an integration circuit, etc., and this signal is amplified by the voltage generation circuit. .

And, by connecting the detection electrode, capacitance change function body, current detector, and voltage generation circuit in series, the output of the voltage generation circuit is connected to the current detector side so that the current flowing through the current detector is reduced to zero. And the output voltage of the voltage generation circuit is controlled to be equal to the voltage of the power line.
According to this prior art, feedback control is performed so that the output voltage of the voltage generation circuit becomes equal to the voltage to be measured, so that it is possible to suppress the influence when the coupling capacitance between the measurement target and the detection electrode varies.

  Next, in the voltage measuring apparatus described in Patent Document 3, a detection probe including an auxiliary capacitor having a predetermined electrostatic capacity is attached to a power line having an insulating coating on a core wire, and a detection capacitor and a voltage are attached to the auxiliary capacitor. A detection circuit is connected, and the AC voltage applied to the core wire is measured by the voltage detection circuit. Here, the detection probe has a flexible insulating member that can be wound around the outside of the insulation of the power line, a first electrode having a large area on the power line side, and a second electrode for voltage detection that faces a part of the first electrode. Are arranged at a predetermined interval, and the whole is integrally formed by drawing a measurement line from the second electrode. Note that the capacity of the auxiliary capacitor is set to a value sufficiently smaller than the capacitance between the core of the power line and the first electrode.

  In Patent Document 3, by using the detection probe as described above, the input voltage of the voltage detection circuit is almost determined by the ratio between the capacitance between the first electrode and the second electrode and the capacitance of the detection capacitor. The influence of fluctuations in the coupling capacity can be suppressed.

JP 2007-163415 A (paragraphs [0036] to [0054], FIG. 1, etc.) JP 2009-162608 A (paragraphs [0037] to [0051], FIG. 1, etc.) JP 2012-163394 A (paragraphs [0022] to [0035], FIGS. 1 to 3 etc.)

In the voltage measuring devices according to Patent Documents 1 and 2, this voltage is matched with the voltage of the power line by controlling the output voltage of the voltage generation circuit fed back to the current detector side. However, an error based on proportional control occurs in the feedback control, and this error varies depending on the magnitude of the detection signal obtained by the current detector and the gain of the amplifier circuit at the subsequent stage.
Here, the larger the detection signal obtained by the current detector and the larger the gain of the subsequent amplifier circuit, the smaller the error. For this reason, in this type of voltage measurement apparatus, an allowable error is determined in consideration of measurement accuracy and the like, and the gain of the amplifier circuit is determined so as to correspond to the error.

  However, if the gain of the amplifier circuit is increased too much in order to reduce the allowable error, the stability and noise resistance of the feedback circuit are lowered, and sufficient measurement accuracy and reliability cannot be obtained. As another method for obtaining the desired accuracy by reducing the gain of the amplifier circuit as much as possible, it is conceivable to increase the detection signal by the current detector. However, the coupling capacity between the core of the power line and the detection electrode is several. Since it is as small as [pF], the current flowing through the current detector is almost determined by the coupling capacitance. This coupling capacitance is proportional to the area of the detection electrode and the dielectric constant, and inversely proportional to the distance between the core wire and the detection electrode. Therefore, the distance between the core wire and the detection electrode is made as short as possible, and the area of the detection electrode and It is necessary to make the dielectric constant as large as possible.

  However, the techniques disclosed in Patent Documents 1 and 2 have a structure in which a detection electrode is built in a case having a through-hole through which a power line penetrates and having a fixed shape. For this reason, for example, when a case having a through hole adapted to a thick power line diameter is applied to a thin power line diameter, the distance between the core line of the power line and the detection electrode is increased, and the distance between the core line and the detection electrode is increased. Since the dielectric constant is lowered by the air present and the coupling capacitance is reduced, sufficient measurement accuracy cannot be obtained.

  Further, in the voltage measuring devices according to Patent Documents 1 and 2, since the capacitance changing function body that changes the impedance in order to modulate the detection signal is connected in series between the detection electrode and the current detector, the capacitance change The drive signal (drive current) of the functional body may be detected as a noise component by the current detector, which may affect the measurement accuracy. As a countermeasure, in these voltage measuring devices, the capacitance changing function body is configured by a bridge made of a diode or the like so that the drive signal component is not detected by the current detector, but the equilibrium state of the bridge is strictly controlled. There is a risk that manufacturing or adjustment costs may increase.

In the voltage measuring device disclosed in Patent Document 3, since the detection signal is determined by the ratio of the capacity of the auxiliary capacitor and the capacity of the detection capacitor, it is necessary to always maintain the capacity of each capacitor with high accuracy. However, since the dielectric constant of the insulating member changes due to the influence of the ambient temperature or the like, it is difficult to always keep the capacitance of the auxiliary capacitor and the detection capacitor formed inside the insulating member with high accuracy.
Furthermore, taking into account the fact that the positional relationship of the detection electrodes is shifted due to the influence of the stress applied to the flexible detection probe during mounting, and the capacitance of the auxiliary capacitor that requires a small capacitance is likely to change, the voltage is measured with high accuracy. It is even more difficult.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a voltage measuring device that can measure a voltage applied to a core of a power line with low cost and high accuracy.

In order to solve the above-described problem, the invention according to claim 1 is a voltage measuring device that measures a voltage to be measured applied to a core wire of a power line using a detection electrode attached to the power line.
A modulation circuit that modulates the current flowing through the coupling capacitance between the core wire and the detection electrode to a frequency higher than the frequency of the voltage to be measured by turning on / off the switching element; and driving for driving the switching element A drive circuit for generating a signal, a current detection circuit connected in series to the switching element to generate a detection signal having a magnitude proportional to a potential difference between the voltage to be measured and a reference potential, and the signal to be measured from the detection signal A demodulating circuit for extracting a frequency component of the voltage; an amplifying circuit for amplifying the output signal of the demodulating circuit; and generating the reference potential such that a current flowing through the current detecting circuit is reduced based on the output signal of the amplifying circuit And a voltage generation circuit to be applied to the current detection circuit,
The voltage to be measured is identified based on the reference potential when the potential difference becomes a predetermined value or less, and the detection electrode incorporates a metal thin film connected to the switching element in an insulating member, thereby It has the flexibility which can be wound around the outer peripheral surface of a power line.

The invention according to claim 2 is a voltage measuring device for measuring a voltage to be measured applied to a core wire of a power line using a detection electrode attached to the power line.
A modulation circuit that modulates the current flowing through the coupling capacitance between the core wire and the detection electrode to a frequency higher than the frequency of the voltage to be measured by turning on / off the switching element; and driving for driving the switching element A drive circuit for generating a signal; a current detection circuit connected in parallel to the switching element to generate a detection signal having a magnitude proportional to a potential difference between the voltage to be measured and the reference potential; and A demodulating circuit for extracting a frequency component of the measurement voltage, an amplifying circuit for amplifying the output signal of the demodulating circuit, and the reference potential that reduces the current flowing through the current detection circuit based on the output signal of the amplifying circuit. A voltage generation circuit that generates and applies to the current detection circuit,
The voltage to be measured is identified based on the reference potential when the potential difference becomes a predetermined value or less, and the detection electrode incorporates a metal thin film connected to the switching element in an insulating member, thereby It has the flexibility which can be wound around the outer peripheral surface of a power line.

  According to a third aspect of the present invention, in the voltage measuring apparatus according to the first or second aspect, the current detection circuit is connected to the primary winding excited by the current flowing through the switching element and the demodulation circuit. And a transformer having a next winding.

  According to a fourth aspect of the present invention, in the voltage measurement device according to any one of the first to third aspects, the amplifier circuit has a function of delaying the phase of the output signal of the demodulator circuit by 90 degrees in electrical angle. Is.

  The invention according to claim 5 is the voltage measuring device according to any one of claims 1 to 4, wherein a MOS-FET is used as the switching element.

According to the present invention, since the detection signal is modulated by turning on / off the switching element instead of the capacitance change function body configured by the bridge circuit, strict management of the equilibrium state of the bridge is unnecessary. Manufacturing or adjustment costs can be reduced.
Furthermore, since the detection electrode configured by incorporating the metal thin film in the insulating member has flexibility that can be wound around the outer peripheral surface of the power line, the detection electrode can be mounted in a state of being in close contact with the power line. Thereby, there is no fear that the positional relationship between the core wire and the detection electrode (metal thin film) is shifted, and there is no fear that the coupling capacitance between the two changes, so that the voltage of the power line can be measured with high accuracy. In addition, since the flexible detection electrode can be attached to power lines having various diameters, there is an advantage that the range of the voltage to be measured is wide.

It is a lineblock diagram of the voltage measuring device concerning a 1st embodiment of the present invention. It is a figure which shows the structure of the power line and detection electrode in each embodiment of this invention. It is a block diagram of the detection circuit in 1st Embodiment of this invention. It is a block diagram of the amplifier circuit in each embodiment of this invention. It is a block diagram of the detection circuit in 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram of a voltage measuring apparatus according to a first embodiment of the present invention.
This voltage measuring apparatus is connected to a detection electrode (detection probe) 2 that measures the AC voltage v ₁ applied to the core wire 1 a of the power line 1 by the system power supply G in a non-contact manner with respect to the core wire 1 a, and to this detection electrode 2. The detection circuit 3 is provided. C ₀ is a coupling capacitance between the core wire 1 a and the detection electrode 2 formed when the detection electrode 2 is attached to the power line 1.
Hereinafter, the voltage (measured voltage) v ₁ of the core wire 1 a is described as being synonymous with “voltage of the power line 1”.

FIG. 2 is a diagram showing the structure of the power line 1 and the detection electrode 2.
The power line 1 includes the core wire 1a and the insulating coating 1b described above. The detection electrode 2 includes a metal thin film 2a connected to a switching element 311 in a modulation circuit 31 (described later) in an insulating member 2b. The detection electrode 2 has various diameters by having flexibility and flexibility as a whole. It is comprised so that it can wind around the power line 1 which has this, in the state closely_contact | adhered to the outer peripheral surface of the insulation coating 1b.

Returning to FIG. 1, the detection circuit 3 includes a modulation circuit 31 connected to the detection electrode 2 and a transformer 32 such as an insulation type pulse transformer as a current detection circuit.
FIG. 3 is a configuration diagram of the modulation circuit 31. The modulation circuit 31 includes two switching elements 311 and 312 connected in series in opposite directions between the detection electrode 2 and the primary winding of the transformer 32. I have. The other end of the primary winding of the transformer 32 is connected to the output side of a high voltage generation circuit 6 described later.

Voltage v ₁ of the core wire 1a to be measured in this embodiment, since for instance an alternating voltage of a commercial frequency, the current flowing through the switching element 311, 312 is the positive and negative directions. The switching elements 311 and 312 are for modulating the current at a frequency sufficiently higher than the frequency of the voltage v ₁ , and are FETs (Field Effect Transistors) that are voltage control elements rather than bipolar transistors that are current control elements. It is desirable to use

There are two types of FETs: J-FET (junction FET) and MOS-FET (metal oxide semiconductor FET), and a depletion type and gate voltage that require a negative bias in the gate voltage to cut off the drain current. There is an enhancement type that can cut the drain current by setting it to 0 [V]. In the present embodiment, if enhancement type MOS-FETs are used for the switching elements 311 and 312, the configuration of the drive circuit 8 to be described later can be simplified.
Further, since the MOS-FET can pass a reverse current through a parasitic diode inside the element, if the switching elements 311 and 312 are connected in series in the reverse direction as shown in FIG. It becomes possible.

In FIG. 3, when a positive bias is applied between the gate and source of the switching elements 311, 312 and current flows in the direction of arrow A, current flows from the drain to the source of the switching element 311, and further, the switching element 312. Current flows in the parasitic diode between the source and drain of the transistor. When a negative bias is applied between the gate and source of the switching elements 311 and 312 and current flows in the direction of arrow B, current flows from the drain to the source of the switching element 312, and further, the source of the switching element 311・ Current flows through the parasitic diode between the drains.
Note that reference numeral 313 in FIG. 3 denotes a resistor connected between the gate and source of the switching elements 311 and 312.

As shown in FIGS. 1 and 3, the secondary winding of the transformer 82 in the drive circuit 8 is connected between the gate and source of the switching elements 311 and 312. Further, the drive circuit 8 includes an oscillation circuit 81 connected to the primary winding of the transformer 82.
The oscillation circuit 81 outputs a rectangular-wave drive signal S ₁ having a frequency (several hundreds [kHz] to several [MHz]) sufficiently higher than a voltage v ₁ having a commercial frequency (50 or 60 [Hz]), and a transformer The switching elements 311 and 312 are turned on / off via 82.

For this reason, the current flowing through the switching elements 311 and 312 via the coupling capacitor C ₀ is modulated by the frequency of the drive signal S ₁ . Thus, in proportion to the magnitude of the current flowing through the switching element 311 and 312, and the detection signal S ₂ of the high frequency is transmitted to the demodulation circuit 4 consisting of C-MOS multiplexer or the like via a transformer 32. Here, the detection signal S ₂ output from the secondary winding of the transformer 32 includes a voltage v ₁ of the power line 1, a magnitude proportional to the potential difference between the reference potential output from the high voltage generating circuit 6 to be described later Have.

The demodulating circuit 4 demodulates the commercial frequency component of the voltage v ₁ of the power line 1, and the demodulated signal is amplified by the subsequent amplifying circuit 5. Incidentally, the demodulation circuit 4, the drive signals S ₁ from the oscillation circuit 81 described above is used to set the timing for detecting the detection signal S _2.

FIG. 4 is a circuit diagram illustrating a configuration example of the amplifier circuit 5.
The amplifier circuit 5 includes a differential amplifying unit 51 including resistors 51b to 51e and an operational amplifier 51a for determining an amplification factor, and a secondary active low pass including an operational amplifier 52a, resistors 52b to 52d, and capacitors 52e and 52f. It has an amplifying unit 52 with a filter function, and an amplifying unit 53 with a primary high-pass filter function including an operational amplifier 53a, resistors 53b to 53d, and a capacitor 53e.

In the detection circuit 3 described above, the voltage v ₁ of the power line ₁ is detected from the current flowing through the coupling capacitor C ₀ by turning on / off the switching elements 311 and 312, and the phase of the output signal of the modulation circuit 4 is the voltage v It is 90 ° ahead of the phase of ₁ . Therefore, if the delayed by a phase of 90 ° of the appropriately set to an output signal of the modulating circuit 4 to the time constant of the plurality of resistors and capacitors in each amplification unit 51 to 53, the amplification circuit 5, the voltage v ₁ and the same phase The analog signal can be generated. In addition, since a kind of band-pass filter composed of the amplifying units 52 and 53 passes only the commercial frequency band, it is possible to reliably remove the high-frequency noise generated when the switching elements 311 and 312 are turned on / off.

The output signal of the amplifier circuit 5 is amplified by, for example, a high voltage generation circuit 6 that performs class D amplification, and is applied to the other end (non-modulation circuit 31 side) of the primary winding of the transformer 32 as a reference potential.
The high voltage generation circuit 6 outputs the reference potential so that the potential difference from the voltage v ₁ applied to one end of the primary winding of the transformer 32 is small, that is, the current flowing through the primary winding is small. The voltage dividing circuit 9 divides the reference potential by a preset voltage dividing ratio and outputs it. For this reason, for example, the zero cross point of the output signal of the amplifier circuit 5 can be detected by an A / D converter (not shown), and the voltage v ₁ of the power line 1 can be measured from the output voltage of the voltage dividing circuit 9 at that time. .

According to this voltage measuring apparatus, it is possible to reduce measurement errors caused by deviations caused by feedback control, and as a result, it is possible to measure the voltage v ₁ of the power line 1 (core line 1a) with high accuracy. In addition, as described in Patent Documents 1 to 3, by not using a bridge configuration capacity change function body, it is not necessary to manage the equilibrium state of the bridge, and there is no risk of increasing manufacturing or adjustment costs. .

Furthermore, the detection electrode 2 can be mounted in a state of being in close contact with the power line 1 by utilizing the flexibility of the detection electrode 2. Thereby, there is no fear that the positional relationship between the core wire 1a and the metal thin film 2a is deviated, and there is no fear that the coupling capacitance C ₀ between the two changes, so the voltage v ₁ can be measured with high accuracy. In addition, since the flexible detection electrode 2 can be attached to the power line 1 having various diameters, there is an advantage that the range of the voltage to be measured is widened.

Next, FIG. 5 is a configuration diagram of a detection circuit in the second embodiment of the present invention.
In the detection circuit 3A of the present embodiment, a modulation circuit 31 including switching elements 311 and 312 is connected in parallel to a series circuit of a primary winding of a transformer 32 as a current detection circuit and a resistor 314. Other configurations are the same as those of the detection circuit 3 in the first embodiment.
According to this embodiment, since the switching elements 311 and 312 are transformer 32 when an OFF is energized, the detection signal by setting the detection timing based on a signal obtained by inverting the demodulation circuit 4, the drive signals S ₁ detection of S ₂ is possible.

  The voltage measuring device of the present invention may be used alone, or a power measuring device can be configured by combining this voltage measuring device and a known current measuring device.

G: System power supply 1: Power line 1a: Core wire 1b: Insulation coating 2: Detection electrode 2a: Metal thin film 2b: Insulation member 3, 3A: Detection circuit 31: Modulation circuit 311, 312: Semiconductor switching elements 313, 314: Resistance 32: Transformer (current detection circuit)
4: Demodulator 5: Amplifier 51: Differential amplifier 51a: Operational amplifiers 51b-51e: Resistor 52: Amplifier with active low-pass filter function 52a: Operational amplifiers 52b-52d: Resistors 52e, 52f: Capacitor 53: High-pass filter Amplifier 53a with function: operational amplifiers 53b to 53d: resistor 53e: capacitor 6: high voltage generation circuit 8: drive circuit 81: oscillation circuit 82: transformer 9: voltage dividing circuit

Claims (5)

In a voltage measuring device that measures a voltage to be measured applied to the core of a power line using a detection electrode attached to the power line,
A modulation circuit that modulates the current flowing through the coupling capacitance between the core wire and the detection electrode to a frequency higher than the frequency of the voltage to be measured by turning on / off the switching element; and driving for driving the switching element A drive circuit for generating a signal, a current detection circuit connected in series to the switching element to generate a detection signal having a magnitude proportional to a potential difference between the voltage to be measured and a reference potential, and the signal to be measured from the detection signal A demodulating circuit for extracting a frequency component of the voltage; an amplifying circuit for amplifying the output signal of the demodulating circuit; and generating the reference potential such that a current flowing through the current detecting circuit is reduced based on the output signal of the amplifying circuit And a voltage generation circuit to be applied to the current detection circuit,
Identifying the voltage to be measured based on the reference potential when the potential difference is less than or equal to a predetermined value;
The voltage detection device according to claim 1, wherein the detection electrode has flexibility that can be wound around an outer peripheral surface of the power line by incorporating a metal thin film connected to the switching element in an insulating member. In a voltage measuring device that measures a voltage to be measured applied to the core of a power line using a detection electrode attached to the power line,
A modulation circuit that modulates the current flowing through the coupling capacitance between the core wire and the detection electrode to a frequency higher than the frequency of the voltage to be measured by turning on / off the switching element; and driving for driving the switching element A drive circuit for generating a signal; a current detection circuit connected in parallel to the switching element to generate a detection signal having a magnitude proportional to a potential difference between the voltage to be measured and the reference potential; and A demodulating circuit for extracting a frequency component of the measurement voltage, an amplifying circuit for amplifying the output signal of the demodulating circuit, and the reference potential that reduces the current flowing through the current detection circuit based on the output signal of the amplifying circuit. A voltage generation circuit that generates and applies to the current detection circuit,
Identifying the voltage to be measured based on the reference potential when the potential difference is less than or equal to a predetermined value;
The voltage detection device according to claim 1, wherein the detection electrode has flexibility that can be wound around an outer peripheral surface of the power line by incorporating a metal thin film connected to the switching element in an insulating member. In the voltage measuring device according to claim 1 or 2,
The voltage measuring device, wherein the current detection circuit is a transformer including a primary winding excited by a current flowing through the switching element and a secondary winding connected to the demodulation circuit. In the voltage measuring device according to any one of claims 1 to 3,
The voltage measuring device, wherein the amplifier circuit has a function of delaying the phase of the output signal of the demodulator circuit by 90 degrees in electrical angle. In the voltage measuring device according to any one of claims 1 to 4,
A voltage measuring apparatus using a MOS-FET as the switching element.

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