JPH11176638A - Remanence demagnetizing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device which can demagnetize residual magnetism in a transformer iron core in a simple manner without stopping a primary circuit. SOLUTION: A device circuit for demagnetizing remanence in a transformer ion core includes a current detecting resistor 5, a variable resistor 6 connected in series with the resistor 5, a transformer a secondary winding 1 of which is connected to both ends of a series circuit of the resistors 5 and 6, and a saturation detecting device connected at both ends of the resistor 5. Since the residual magnetism in the transformer can be reduced by increasing or decreasing the resistive value of the variable resistor 6, there can be provided with a small-size remanence demagnetizing device which can demagnetize residual magnetism in a transformer ion core easily in a short time without stopping a primary circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current transformer, and more particularly, to a remanence demagnetizing device for a current transformer core using a closed magnetic core.

[0002]

2. Description of the Related Art Normally, a current transformer is composed of an iron core serving as a path for magnetic flux, a winding serving as a path for a current interlinking with the magnetic flux, an insulator for insulating them, a mounting member for mounting the apparatus, and the like. It is configured and attached to the devices that make up the power system, and performs accurate power system protection and current measurement.

However, in an electric power system, the fault point is separated from the system in the event of a ground fault or the like, so that residual magnetism remains in the current transformer core depending on the interruption phase of the fault current. If the operation is started with the residual magnetism remaining, the current transformer core may be saturated with a current less than the guaranteed current, which may cause a malfunction of the relay.

[0004]

In order to eliminate this residual magnetism, as shown in FIG. 6, a current detecting resistor 2 and an AC power supply 3 are connected to a secondary winding 1 of a current transformer attached to a device. Observe the voltage waveform with the oscilloscope 4 connected in series and connected to both ends of the current detecting resistor 2 while increasing the voltage,
A method of gradually lowering the voltage at the time of saturation is generally used. However, according to this method, it is necessary to stop the primary circuit, and in the case of a power system, a large amount of work is required.

The present invention has been made in view of the above circumstances, and has as its object to provide a current transformer core capable of eliminating the residual magnetism of the current transformer core without stopping the primary circuit by a simple method. Another object of the present invention is to provide a remanent demagnetization device.

[0006]

To achieve the above object, a first aspect of the present invention is that a current detecting resistor and a variable resistor connected in series have both ends connected to terminals of a secondary winding of a current transformer. A residual magnetic demagnetization device circuit of a current transformer core, wherein a saturation detection device is connected to both ends of the current detection resistor.
The remanence of the current transformer can be demagnetized by increasing or decreasing the resistance value of the variable resistor.

According to the first aspect, the voltage applied to the secondary winding of the current transformer increases in proportion to the resistance value of the variable resistor,
On the polarity side with remanence, the current transformer core is saturated first, and when the resistance is further increased, both the + side and the-side are saturated. After confirming the saturation with the saturation detecting device, the resistance value is reduced continuously and the secondary winding of the current transformer is short-circuited to reduce the hysteresis loop of the iron core, so that the residual magnetism is demagnetized.

According to a second aspect of the present invention, in the residual magnetic demagnetizing device for a current transformer core according to the first aspect, the resistance value of the variable resistor is increased or decreased by an electric motor. According to the second aspect, the voltage applied to the secondary winding of the current transformer increases in proportion to the resistance value of the variable resistor, and the current transformer core first saturates on the polarity side where the remanence is present. Increasing the resistance saturates both the + and-sides. After saturation, the residual magnetism is demagnetized by continuously lowering the resistance value with the motor and short-circuiting the secondary winding of the current transformer. All of these operations are performed automatically.

According to a third aspect of the present invention, there is provided the residual magnetic demagnetizer for a current transformer core according to the first aspect, further comprising a composite circuit in which a fixed resistor and a semiconductor switch are connected in multiple stages in place of the variable resistor. It is characterized in that the resistance value is increased or decreased by controlling the semiconductor switch.

According to the third aspect, the voltage applied to the secondary winding of the current transformer increases in a stepwise manner in proportion to the resistance value of the turned-on resistor, and the current transformer core is provided on the polarity side where there is residual magnetism. Saturates first. When the resistance value is further increased, both the + side and the-side are saturated. After saturation, the remanence is demagnetized by lowering the resistance and shorting the current transformer secondary winding.

According to a fourth aspect of the present invention, in the residual magnetic demagnetizing device for a current transformer core according to the third aspect, the fixed resistors of the multi-stage connected composite circuit are connected such that the resistance value increases in order. When the resistance value is increased by the semiconductor switch, control is performed from a fixed resistance having a small resistance value, and when the resistance value is reduced by the semiconductor switch, control is performed from a fixed resistance having a large resistance value.

According to the fourth aspect, the voltage applied to the secondary winding of the current transformer increases stepwise in proportion to the resistance value of the turned-on resistance, and the current transformer core is provided on the polarity side where there is residual magnetism. Saturates first. When the resistance value is further increased, both the + side and the-side are saturated. After saturation, the resistance is reduced and the current transformer secondary winding is short-circuited.However, the step width of the voltage applied to the secondary winding decreases as the voltage decreases, so that the residual magnetism is more effectively demagnetized. You.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a first embodiment (corresponding to claim 1) of the present invention. As shown in the figure, in the remanent magnetic demagnetization device for a transformer core of the present embodiment, a current detecting resistor 5 and a variable resistor 6 are connected in series.
, A saturation detection device, that is, a comparison circuit 8 connected in parallel with a high-pass filter 7 and a saturation detection display 9 are connected. Further, the resistance value of the variable resistor 6 can be continuously increased and decreased, and the above circuit configuration is connected to the terminal of the current transformer secondary winding 1.

Next, the operation of this embodiment will be described.
When the resistance value of the variable resistor 6 is continuously increased, the current transformer core is saturated on the polarity side with the residual magnetism. When the core is saturated, the current waveform is distorted as shown by the solid line 10 in FIG.
Unlike the current waveform at the time of non-saturation (broken line 11), a harmonic component is generated. This current waveform is converted into a voltage waveform by the current detection resistor 5 and passed through the high-pass filter 7 so that only harmonic components are input to the respective parallel-connected comparator circuits 8. One comparison circuit 8 is for detecting the + side saturation, and the other comparison circuit 8 is for detecting the − side saturation. The output of each comparator 8 is inverted when saturation is detected, and the saturation can be confirmed by the respective saturation detection indicators 9. After confirming saturation on both the + side and the-side, the resistance value of the variable resistor 6 is continuously reduced and short-circuited, so that residual magnetism can be erased.

Therefore, in this embodiment, since electric power is supplied from the primary circuit, an external power supply is not required.
The demagnetization circuit can be downsized. Further, since the saturation can be confirmed by the display 9, the demagnetization can be performed safely and easily in a short time.

FIG. 3 is a circuit diagram of a second embodiment (corresponding to claim 2) of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals. As shown in the figure, the residual magnetic demagnetizing device for a transformer core according to the present embodiment has a current detecting resistor 5 and a variable resistor 6 connected in series, and a saturation detecting device, that is, a high-pass Filters 7 and 2
The comparison circuits 8 and the AND circuit 12 are connected. The resistance value of the variable resistor 6 can be increased or decreased by an electric motor 13, and a switch 14 is connected to the electric motor 13, and a circuit is configured such that the switch 14 is inverted by an output of the AND circuit 12. Also, the variable resistance 6 can be increased or decreased by inverting the electric motor 13, and the above circuit configuration is connected to the terminal of the current transformer secondary winding 1.

Next, the operation of the present embodiment will be described.
When the resistance value of the variable resistor 6 is increased by driving the electric motor 13, the current transformer core is saturated on the polarity side with the residual magnetism,
The current waveform is distorted as shown by the solid line 10 in FIG. This current waveform is converted into a voltage waveform by the current detection resistor 5 and passed through the high-pass filter 7 so that only the harmonic component is input to the comparison circuit 8. Two comparison circuits 8 are connected in parallel. One comparison circuit 8 is for detecting the saturation on the positive side, and the other comparison circuit 8 is for detecting the saturation on the negative side. The output of the comparison circuit 8 is inverted when saturation is detected. When both the + and − comparison circuits 8 are saturated, a signal is sent from the AND circuit 12 to the switch 14 and the motor 13 is reversed. As a result, the resistance value of the variable resistor 6 decreases, and the residual magnetism can be erased.

Therefore, in this embodiment, since power is supplied from the primary circuit, an external power supply is not required.
The demagnetizing circuit can be downsized. In addition, since the demagnetization can be performed automatically by operating the electric motor 13, the demagnetization can be performed safely and easily in a short time. The electric motor 13 is driven by a dry battery or the like.

FIG. 4 is a circuit diagram of a third embodiment of the present invention. The same components as those in the second embodiment will be described with the same reference numerals. As shown in the figure, the remanent magnetic demagnetization device for a transformer core according to the present embodiment includes a current detecting resistor 5 and a fixed resistor 1.
5 and a semiconductor switch 16 are connected in series in a ladder configuration, and a saturation detection device, that is, a high-pass filter 7, two comparison circuits 8 and an AND circuit 12 are connected to both ends of the current detection resistor 5. I have. A control circuit 17 for controlling the semiconductor switch is connected to the semiconductor switch 16, and the control circuit 17 outputs 0 → 1
The circuit is configured to invert when it becomes. This circuit configuration is connected to the terminals of the current transformer secondary winding 1.

Next, the operation of this embodiment will be described.
When the control circuit 17 connected to the semiconductor switch 16 is operated, the semiconductor switch 16 is opened and a current flows through the fixed resistor 15, and a voltage is applied to the secondary winding 1 of the current transformer. When the semiconductor switch is opened from the connection terminal side with the current transformer secondary winding 1 and the current transformer core is saturated on the polarity side with residual magnetism, the current waveform is distorted as shown by the solid line 10 in FIG. . This current waveform is applied to the current detection resistor 5
By converting the voltage into a voltage waveform through the high-pass filter 7, only the harmonic components are input to the comparison circuit 8. Two comparison circuits 8 are connected in parallel. One comparison circuit 8 is for detecting the saturation on the positive side, and the other comparison circuit 8 is for detecting the saturation on the negative side. Comparison circuit 8
Output is inverted when saturation is detected.
When the comparator circuit 8 on both the + side and the − side saturates, the AND circuit 1
2 sends a signal to the control circuit 17 and the semiconductor switch 16
Is conducted. By operating the control circuit 17 to turn on the semiconductor switch 16 in the reverse order of opening, the residual magnetism can be erased.

Therefore, in this embodiment, since power is supplied from the primary circuit, an external power supply is not required.
The demagnetizing circuit can be downsized. In addition, demagnetization can be performed automatically without a driving section, and demagnetization can be performed safely, easily, and in a short time.

FIG. 5 is a circuit diagram of a fourth embodiment of the present invention. As shown in the figure, the difference between the remnant magnetic demagnetizer of the transformer core of the present embodiment and the third embodiment is that
a. 15c are only the configuration in which the resistance 15a to be conducted first is smaller and the resistance 15b,... 15c is increased in the order of the resistance 15b, and the other configuration is the same. Are denoted by the same reference numerals, and description thereof is omitted.

Next, the operation of this embodiment will be described.
When the control circuit 17 connected to the semiconductor switch 16 is operated, the semiconductor switch 16 is opened and current flows through the fixed resistor 15a.
Is applied with a voltage. The fixed resistance value is 15a <15b ...
The fixed resistors are connected so as to increase in order from the resistor to be turned on first so as to be <15c. Current transformer secondary winding 1
From the semiconductor switch 16 on the connection terminal side of
The current flows in the order of the fixed resistors 15a, 15b,... 15c. When the applied voltage increases, the current transformer core saturates on the polarity side where there is residual magnetism, and the current waveform is distorted as shown by the solid line 10 in FIG. This current waveform is converted into a voltage waveform by the current detection resistor 5 and passed through the high-pass filter 7, so that only the harmonic component is input to the comparison circuit 8. Two comparison circuits 8 are connected in parallel. One comparison circuit 8 is for detecting the saturation on the positive side, and the other comparison circuit 8 is for detecting the saturation on the negative side. The output of the comparison circuit 8 is inverted when the saturation is detected. When the output of the comparison circuit 8 is saturated by both the + side and the − side, a signal is sent from the AND circuit 12 to the control circuit 17 and the output is inverted. Thereby, the control circuit 1
By operating the semiconductor switch 16 to turn on the semiconductor switch 16 in the reverse order of opening, starting from the fixed resistor 15c having the larger resistance value, the residual magnetism can be more effectively erased.

Therefore, in this embodiment, since power is supplied from the primary circuit, an external power supply is not required.
The demagnetizing circuit can be downsized. In addition, since the fixed resistance value is gradually reduced as the applied voltage decreases, the residual magnetism can be effectively erased, and the demagnetization can be performed safely, easily, and in a short time.

It should be noted that the present invention is not limited to the embodiments described above, and the shapes, sizes, numbers, and the like of the constituent members can be appropriately changed. For example, high-pass filter 7
Instead, a similar effect can be expected by using a band-pass filter that passes a higher harmonic region. Similar effects can be obtained by using a NAND circuit instead of the AND circuit. Further, by connecting a plurality of variable resistors 6 in the first and second embodiments in series, a wider range of demagnetization work can be performed.

[0026]

As described above, the present invention (Claim 1)
According to the fourth aspect of the present invention, the residual magnetism demagnetizing device can easily and quickly demagnetize the residual magnetism of the current transformer core without stopping the primary circuit. Can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is a current waveform diagram when a current transformer core is saturated.

FIG. 3 is a circuit diagram of a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a third embodiment of the present invention.

FIG. 5 is a circuit diagram of a fourth embodiment of the present invention.

FIG. 6 is a circuit diagram of a conventional residual magnetic demagnetizing device for a current transformer core.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Current transformer secondary winding, 2 ... Current detection resistance, 3 ... AC power supply, 4 ... Oscilloscope, 5 ... Current detection resistance, 6 ... Variable resistance, 7 ... High-pass filter, 8 ... Comparison circuit, 9 ... Saturation detection display, 10: current waveform at saturation, 11: current waveform at non-saturation, 12: AND circuit, 13: electric motor, 1
4 switches, 15, 15a, 15b, 15c fixed resistors, 16 semiconductor switches, 17 control circuits.

Claims (4)

[Claims] 1. A transformer in which both ends of a current detecting resistor and a variable resistor connected in series are connected to terminals of a current transformer secondary winding, and a saturation detecting device is connected to both ends of the current detecting resistor. A residual magnet demagnetization device circuit for a current transformer core, wherein the residual magnetism of the current transformer can be demagnetized by increasing or decreasing the resistance value of the variable resistor. Demagnetizer. 2. The residual magnetic demagnetization device for a current transformer core according to claim 1, wherein the resistance value of the variable resistor is increased or decreased by an electric motor. 3. The residual magnetic demagnetization device for a current transformer core according to claim 1, further comprising a composite circuit in which a fixed resistor and a semiconductor switch are connected in multiple stages, instead of the variable resistor, to control the semiconductor switch. A residual magnetic demagnetization device for a current transformer core, the resistance value of which increases or decreases due to the change in resistance. 4. The residual magnetic demagnetization device for a current transformer core according to claim 3, wherein the fixed resistors of the multi-stage connected composite circuit are connected so that their resistance values become higher in order, and the semiconductor switch is When increasing the resistance value, control is performed from a fixed resistance having a small resistance value, and when decreasing the resistance value by the semiconductor switch, control is performed from a fixed resistance having a large resistance value. Porcelain device.