JPH08236351A - Erasing method of residual magnetic flux of current transformer core and demagnetizing device - Google Patents

Abstract

PURPOSE: To provide a method of erasing the residual magnetic flux of a current transformer core and a demagnetizing device, wherein the magnetizing device is capable of erasing a residual magnetic flux with a power supply of small capacity without inducing a high voltage in the winding wire of an equipment under test. CONSTITUTION: An alternating/direct current overlapping power supply 1 which is capable of feeding an alternating current and a direct current of a low voltage at the same time or an alternating/direct current switch power supply 2 which is capable of alternately feeding an alternating current and a direct current of a low voltage is connected in series to an equipment 3 such as a static induction equipment under test. Furthermore, a frequency analyzer 5 for the waveform of an exciting current of the alternating/direct current overlapping power supply 1 or the alternating/direct current switch power supply 2 is also connected in series to the equipment 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of eliminating residual magnetic flux of a current transformer core and a demagnetizing device for demagnetizing the magnetism remaining in the core of the current transformer before operating the current transformer. .

[0002]

2. Description of the Related Art When a DC or AC voltage is applied to a current transformer such as a static induction device consisting of a winding and an iron core, and a current is passed through the winding and then cut off, the residual magnetic flux is transferred to the iron core of the current transformer. Remains. In this way, if DC magnetism remains in the iron core of the current transformer, for example, if the fault current is applied with 80% DC magnetic flux of the maximum magnetic flux density remaining, the current transformer will simply be overwritten. Only 20% of current range performance is demonstrated.

Therefore, the residual DC magnetism must be demagnetized before the operation of the current transformer, and if it is not demagnetized, it may cause malfunction or malfunction of the protective relay or the like. There is.

Therefore, conventionally, in order to demagnetize the residual magnetic flux to zero, a device as shown in FIG. 9 is used. That is, the EUT 13 such as the stationary induction device is
An instrument transformer 14 is connected in parallel, and an AC power source 12
Are connected in series. The instrument transformer 14
An AC voltmeter 15 is connected in parallel with the AC voltage meter 15, and an oscilloscope 17 for measuring the excitation current waveform is connected in series with the DUT 13 such as a static induction device and the AC power supply 12.

In such a demagnetizing device, the AC power source 1 connected to the device under test 13 such as a static induction device.
2, a predetermined voltage (about 1.1 times the rated voltage) is applied until the iron core of the EUT 13 is sufficiently saturated,
A method of generating an alternating magnetic field as shown in (3) and gradually decreasing the voltage to demagnetize (AC voltage method) was general.

[0006]

However, the above-described conventional method of eliminating the residual magnetic flux of the current transformer core and the demagnetizing apparatus have the following drawbacks. That is,
The above-mentioned method generally requires a large-capacity AC power supply facility, so that the residual magnetic flux cannot be erased in a place where there is no large-capacity power supply facility. In addition, the saturation voltage may be several thousand volts, and a high voltage is generated in the winding of the EUT, which causes a problem in insulation.

The present invention has been proposed in order to solve the problems of the prior art as described above, and an object thereof is to generate a high voltage in a winding of a device under test and to supply a small capacity power source. An object of the present invention is to provide a method for eliminating residual magnetic flux of a current transformer iron core and a demagnetizing device capable of eliminating residual magnetic flux with equipment.

[0008]

According to the method of eliminating residual magnetic flux of a current transformer core according to claim 1, alternating current waveforms of a current transformer are used by alternately or simultaneously using low-voltage AC and DC power supplies. The + side and the-side are subjected to frequency analysis by a frequency analysis device, and the DC power supply is adjusted so that the absolute values of the alternating currents at the respective frequencies become equal.

According to a second aspect of the present invention, the residual magnetic flux of the current transformer iron core is erased by alternately or simultaneously using both low-voltage AC and DC power supplies to frequency-analyze the AC current waveform of the current transformer. The feature is that the DC power supply is adjusted so that only odd harmonics are included without including even harmonics.

Further, in the method for eliminating the residual magnetic flux of the current transformer core according to the third aspect of the present invention, the alternating current waveform of the current transformer is set to + by alternately or simultaneously using both low voltage AC and DC power supplies.
The DC power supply is adjusted so that the absolute values of the peak values on the negative side and the negative side are equal.

According to a fourth aspect of the present invention, there is provided a demagnetization device for residual magnetic flux of a current transformer iron core, wherein a frequency analysis device is connected in series to an AC / DC switching power source in which an AC power source and a DC power source are connected in parallel via a polarity switching device. It is characterized by being connected to.

According to a fifth aspect of the present invention, there is provided a demagnetization device for residual magnetic flux of a current transformer iron core, wherein a frequency analysis device is connected in series to an AC / DC superposed power supply in which an AC power supply and a DC power supply are connected in parallel. Is.

According to a sixth aspect of the present invention, there is provided a demagnetization device for residual magnetic flux of a current transformer iron core, wherein a residual magnetism detector is connected in series to an AC / DC switching power source in which an AC power source and a DC power source are connected in parallel via a polarity switching device. It is characterized by being connected.

According to a seventh aspect of the present invention, there is provided a residual magnetic flux demagnetizing device for a residual current transformer core, wherein a residual magnetism detector is connected in series to an AC / DC superimposing power source in which an AC power source and a DC power source are connected in parallel. It is a thing.

According to an eighth aspect of the present invention, in the apparatus for demagnetizing the residual magnetic flux of the current transformer core according to the sixth or seventh aspect, the residual magnetism detector detects demagnetization of the iron core of the current transformer. And a Hall element for converting the magnetic flux density into a direct current voltage.

[0016]

According to the inventions of claims 1 to 3,
A small-capacity power supply facility can detect a residual magnetic flux zero point without generating a high voltage in a device under test and can eliminate the residual magnetic flux. .

According to the invention described in claims 4 to 8, the residual magnetic flux is erased by detecting the residual magnetic flux zero point in the small-capacity power supply equipment without generating a high voltage in the EUT. It is possible to provide a demagnetization device for the residual magnetic flux of the current transformer iron core.

[0018]

Embodiments of the present invention will be specifically described below with reference to the drawings.

[A. Method of Eliminating Residual Magnetic Flux of Current Transformer Core] [1. First Embodiment] In the present embodiment, as shown in FIG. 1, an AC / DC power supply 1 capable of simultaneously supplying both low-voltage AC and DC to a device under test 3 such as a stationary induction device. Alternatively, an AC / DC switching power supply 2 capable of alternately supplying low voltage AC and DC is connected in series.
A frequency analyzer 5 for frequency-analyzing the waveform of the exciting current excited by the AC / DC superimposing power supply 1 or the AC / DC switching power supply 2 is connected in series to the DUT 3 such as the stationary induction device. . Note that FIG. 2 shows an equivalent circuit of the static induction device. That is, it is equivalent to a circuit in which the winding resistance 6 and the inductance 7 are connected in series.

The method of eliminating the residual magnetic flux of the current transformer core of this embodiment will be described below. That is, when the residual magnetic flux remains in the device under test 3 such as the stationary induction device, the BH curve is as shown by the solid line 9 in FIG. At this time, as described above, when the EUT 13 is excited by using the AC power source 12 as shown in FIG. 9, the excitation current waveform observed by the oscilloscope 17 is as shown in FIG. −
The waveform is asymmetrical with the side, and the absolute values of the peak values are different.

Therefore, the device under test 3 in which such residual magnetic flux remains remains, the AC / DC power supply 1 or AC / DC capable of supplying both low voltage AC and DC at the same time or alternately as shown in FIG. The switching power supply 2 excites, and the waveform of the flowing exciting current is frequency-analyzed by the frequency analyzer 5. Then, when the DC voltage is 0 and only the AC voltage is excited, an asymmetric current similar to that shown in FIG. 4 flows, and there is a difference between the + side and − side frequency components. Then, by supplying the DC current little by little according to the polarity on the higher peak side, there is a point where the + side and − side frequency components become equal, and this is the residual magnetic flux zero point. The current waveform at this time is a symmetrical waveform on the + side and the-side, as shown in FIG.

[2. Second Embodiment] The configuration of this embodiment is the same as that of the first embodiment, and the description thereof will be omitted. The method of detecting the residual magnetic flux zero point is different from that of the first embodiment. That is, also in this embodiment, the DC voltage is 0
In the case of excitation with AC voltage only, the same asymmetric current as shown in FIG. 4 flows, but the result of frequency analysis for one period shows that
There are harmonics that are odd and even times the frequency of the power supply. Here, as in the first embodiment, when a direct current is supplied little by little, the even harmonics become zero. This is the residual magnetic flux zero point. This is because if the frequency analysis result of the measured AC current waveform does not include even harmonics such as 2 times, 4 times, 6 times, etc. of the power supply frequency, the + side and-side waveforms are symmetric. Is used.

[3. Third Embodiment] The configuration of this embodiment is also the same as that of the first embodiment, and the description thereof will be omitted. The method of detecting the residual magnetic flux zero point is different from that of the first embodiment. That is, also in this embodiment, the DC voltage is 0
In the case of excitation with an AC voltage only, an asymmetric current similar to that shown in FIG. 4 flows, but by controlling the DC current so that the absolute values of the + side and-side peak values of this current waveform become equal, The magnetic flux can be erased. This is because the point where the absolute values of the peak values on the + side and − side of the current waveform are equal is the residual magnetic flux zero point.

[B. Demagnetizing device for current transformer core] [1. First Embodiment] A demagnetizing device for a current transformer iron core according to the present embodiment is constructed as shown in FIG. That is, the AC power supply 21 is connected to the DC current generator 2 via the polarity switcher 22.
3 are connected in parallel, and are further connected in series with a current transformer having a current transformer winding 25 and a current transformer core 26, and a residual magnetism detector 24. The residual magnetism detector 24
Is configured by mounting a Hall element on a part of a closed magnetic circuit core. That is, as shown in FIG.
A shunt 32 is connected to the shunt 32, and the shunt 32 is provided with an exciting winding 33 of the residual magnetic detection iron core 3 to detect the residual magnetic detection iron core 3.
4 are connected in parallel. A Hall element 35 is attached to a part of the residual magnetism detecting iron core 34. Further, to the hall element 35, a hall element control current power source 36 and a DC amplifier 37 are connected.

The demagnetizing device for the current transformer iron core of this embodiment having such a structure operates as described below. That is, the output terminal of the demagnetizer is connected to the primary winding or the secondary winding of the current transformer, and the positive output current of the DC current generator 23 is drawn so as to draw the hysteresis as shown in FIG. After increasing to the point A where the iron core saturates, the current is reduced and cut off at the point B. Then, the polarity is reversed, and the negative output current is again increased to the point C where the iron core is saturated and cut off. During this period, the residual magnetism detector 24, in which a Hall element is attached to a part of the closed magnetic circuit core, shows the same positive or negative maximum output voltage, but the same locus as the hysteresis of the current transformer core although the absolute amount is different. I am following.

With the above operation, the magnetism of the current transformer core is
Since it is stopped at the point D of the hysteresis shown in FIG. 7, the same positive current as at the beginning is temporarily increased and the output voltage of the residual magnetism detector 24 indicates the zero point, that is, FIG.
Turn off the power at point E.

By the above operation, the magnetic flux density is about 0 (GA
Since the power supply was cut off in USS), the magnetomotive force returns to the zero point and the residual magnetism is demagnetized. Further, by automating a series of operations using the residual magnetism detector 24 as a sensor, the residual magnetism is demagnetized only by setting the output current to the direct current generator 23 and driving the device, and the operation is further improved. It will be easy.

In this way, the residual magnetic flux demagnetization device of the current transformer iron core of the present embodiment directly connects the residual magnetism detector using the Hall element in series with the current transformer for demagnetization. Regardless of the quantitative magnitude of the residual magnetism of the current transformer core, which is difficult to measure, it is possible to forcibly activate the hysteresis loop by DC excitation and detect the point of magnetic flux density 0 (GAUSS).

[0029]

As described above, according to the present invention, a current transformer core capable of eliminating residual magnetic flux with a small-capacity power supply facility without generating a high voltage in the winding of the EUT. It is possible to provide a residual magnetic flux erasing method and a demagnetizing device.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a method for eliminating residual magnetic flux of a current transformer core which is a first embodiment of the present invention.

FIG. 2 is a diagram showing an equivalent circuit of a stationary induction device.

FIG. 3 is a characteristic diagram showing typical magnetization characteristics.

FIG. 4 is a characteristic diagram showing an example of a current waveform when the EUT has residual magnetic flux.

FIG. 5 is a characteristic diagram showing an example of a current waveform when the EUT has no residual magnetic flux.

FIG. 6 is a circuit diagram showing an embodiment of a demagnetization device for residual magnetic flux of a current transformer core which is a second embodiment of the present invention.

FIG. 7 is a diagram showing a demagnetization hysteresis of residual magnetism of a current transformer.

FIG. 8 is a circuit diagram of a residual magnetism detector used in the second embodiment of the present invention.

FIG. 9 is a circuit diagram showing an example of a conventional method of eliminating residual magnetic flux of a current transformer core.

FIG. 10 is an explanatory diagram of a demagnetization mechanism of residual magnetism due to AC

[Explanation of symbols]

1 ... AC / DC superposed power supply 2 ... AC / DC switching power supply 3 ... Stationary induction device 4 ... Current measuring resistor 5 ... Frequency analysis device 6 ... Stationary induction device winding resistance 7 ... Stationary induction device inductance 8 ... General BH Curve 9 ... BH curve when residual magnetic flux remains in the EUT 12 ... Large capacity AC power supply 13 ... EUT 14 ... Meter transformer 15 ... AC voltmeter 16 ... Current measuring resistance 17 ... Oscilloscope 21 ... AC power supply 22 ... Polarity switch 23 ... DC generator 24 ... Residual magnetism detector 31 ... Energizing main circuit 32 ... Shunter 33 ... Excitation winding of residual magnetism detecting iron core 34 ... Residual magnetism detecting iron core 35 ... Hall element 36 ... Hall element control current power supply 37 ... DC amplifier A point ... Maximum magnetic flux density point of current transformer core due to positive current flow B point ... Residual magnetic flux density point C generated due to interruption of positive current C point ... Negative electrode Point of maximum magnetic flux density of current transformer core due to energization of negative current D point ... Residual magnetic flux density point generated due to interruption of negative current E point ... Residual magnetic flux density 0 (GAUSS) point

Claims (8)

[Claims] 1. A low-voltage alternating current and direct current power source is alternately or simultaneously used to perform frequency analysis on a + side and a − side of an alternating current waveform of a current transformer with a frequency analyzer to determine the alternating current at each frequency. A method of erasing residual magnetic flux of a current transformer core, characterized in that the DC power supply is adjusted so that the absolute values become equal. 2. A direct current power supply such that alternating current and low direct current of low voltage are alternately or simultaneously used for frequency analysis of the alternating current waveform of the current transformer so that only odd harmonics are included without including even harmonics. A method for eliminating residual magnetic flux in a current transformer core, the method comprising: 3. A low-voltage alternating current and direct current power supplies are used alternately or simultaneously, and a direct current power supply is used so that the absolute values of the peak values on the + side and − side of the alternating current waveform of the current transformer are equal. A method for eliminating the residual magnetic flux of a current transformer core, which is characterized by adjusting. 4. A demagnetization of residual magnetic flux of a current transformer core, characterized in that a frequency analysis device is connected in series to an AC / DC switching power supply in which an AC power supply and a DC power supply are connected in parallel via a polarity switching device. apparatus. 5. A demagnetization device for residual magnetic flux of a current transformer core, wherein a frequency analysis device is connected in series to an AC / DC power supply in which an AC power supply and a DC power supply are connected in parallel. 6. The residual magnetic flux reduction of a current transformer core, characterized in that a residual magnetism detector is connected in series to an AC / DC switching power supply in which an AC power supply and a DC power supply are connected in parallel via a polarity switching device. Porcelain device. 7. A demagnetization device for residual magnetic flux of a current transformer core, wherein a residual magnetism detector is connected in series to an AC / DC superimposed power supply in which an AC power supply and a DC power supply are connected in parallel. 8. The residual magnetism detector comprises a shunt for detecting demagnetization of an iron core of a current transformer, a closed magnetic circuit iron core, and a Hall element for converting a magnetic flux density into a DC voltage. The demagnetization device for the residual magnetic flux of the current transformer core according to claim 6 or 7.