JP3842140B2 - Transformer residual flux measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transformer residual magnetic flux measuring device.
[0002]
[Prior art]
FIG. 5 is an explanatory diagram for explaining a conventional residual magnetic flux measurement method described in, for example, Japanese Patent Application Laid-Open No. 2000-275111, in which power supply to the transformer is cut off while the transformer is excited for a sufficient time. It shows the magnetic flux waveform obtained by measuring the change in the induced voltage that sometimes occurs and taking the voltage waveform into a computer and integrating it. The residual magnetic flux Φ1 is the level of the final value Φ2 of the magnetic flux waveform shown in FIG. I asked for it in the form of taking a difference.
[0003]
[Problems to be solved by the invention]
Since conventional residual magnetic flux measurement has been performed as described above, there are the following problems. That is, due to the influence of the DC offset component superimposed on the measurement system, the final value of the magnetic flux waveform obtained by the voltage integration calculation is not constant, and may monotonously increase or decrease monotonically, or a drift with a large time constant may occur. . Also in the magnetic flux waveform shown in FIG. 5, the final value monotonously increases. Therefore, Φ2 varies depending on the time of reading, and there is a problem that an accurate residual magnetic flux Φ1 cannot be calculated. In addition, depending on the impedance of the transformer and the value of the floating capacitance of the peripheral circuit, the decay time of the transient vibration changes from when the power supply to the transformer is cut off until the magnetic flux waveform converges to the final value. There is a problem. In this case, it is possible to read the value after a certain period of time after the power supply is cut off as the residual magnetic flux, but depending on the impedance of the transformer and the floating capacitance of the peripheral circuit, the transient oscillation of the magnetic flux waveform may occur. In some cases, the magnetic flux has not converged. In such a case, there is a problem that an accurate residual magnetic flux cannot be calculated.
[0004]
Also, for each device with different transformer impedance and stray capacitance of the peripheral circuit, measure the attenuation time from the time the power supply is cut off until the transient vibration of the magnetic flux waveform converges, Although it is possible to read the value, in this case, there is a problem in that setting of the reading time becomes complicated because on-site measurement is required.
In order to remove the above-described DC offset, there is a measure to apply a high-pass filter to the voltage signal. However, since the voltage signal after the power supply is cut off is a rectangular wave-like damped oscillation waveform, the waveform is obtained by applying the filter. There is a problem that a large distortion occurs, resulting in an increase in residual magnetic flux error obtained by voltage integration calculation.
The present invention has been made to address the above-described problems, and an object thereof is to provide a transformer residual magnetic flux measuring device capable of accurately reading the residual magnetic flux.
[0005]
[Means for Solving the Problems]
A transformer residual magnetic flux measuring apparatus according to the present invention stores an opening detection means for detecting an opening time of a circuit breaker connected to a power supply circuit of a transformer, and stores a voltage signal of the power supply circuit for a predetermined time. Voltage signal measuring means adapted to measure the voltage signal of the feeder circuit before and after opening of the circuit breaker, and calculating an offset amount of the voltage signal before opening of the circuit breaker, Voltage signal offset removing means for removing the offset from the voltage signal, voltage signal integration interval detecting means for setting the time when the transient vibration of the voltage signal after opening of the circuit breaker is attenuated to a predetermined value or less as the end of integration, a voltage signal integration means for integrating the voltage signal, and the magnetic flux signal calculation means for obtaining a magnetic flux signal by removing the offset before opening of the circuit breaker of the voltage integral signal, a residual magnetic flux from the magnetic flux signal Those having a residual magnetic flux calculation means for calculating.
[0006]
The transformer residual magnetic flux measuring apparatus according to the present invention also obtains an approximate function based on the absolute value of the peak point between the zero cross points of the offset-removed voltage signal after the opening of the circuit breaker. When the calculated value becomes equal to or less than a predetermined value, the voltage signal integration section detecting means terminates the integration of the voltage signal.
[0007]
The transformer residual magnetic flux measuring apparatus according to the present invention also obtains an approximate function based on an absolute value of an average peak value between zero-cross points of the voltage signal after offset removal after opening of the circuit breaker, and this approximate function When the value calculated by the above is less than or equal to a predetermined value, the voltage signal integration interval detecting means terminates the integration of the voltage signal.
[0008]
The residual magnetic flux measuring device for a transformer according to the present invention further includes an opening detection means for detecting an opening time of a circuit breaker connected to the power supply circuit of the transformer, and stores a voltage signal of the power supply circuit for a predetermined time. And a voltage signal measuring means adapted to measure the voltage signal of the feeder circuit before and after opening of the circuit breaker and a transformer current signal of the transformer for a predetermined time. A transformer current signal measuring means capable of measuring a transformer current signal before and after opening of the circuit breaker, and calculating an offset amount of the voltage signal before opening of the circuit breaker. Voltage signal offset removal means for removing offset from the voltage signal integration interval detection means for setting the time when the transient vibration of the transformer current signal after opening of the circuit breaker is attenuated below a predetermined value as the end of integration; Residual calculating a voltage signal integration means for integrating the voltage signal, and the magnetic flux signal calculation means for obtaining a magnetic flux signal by removing the offset before opening of the circuit breaker of the voltage integral signal, a residual magnetic flux value from the magnetic flux signal Magnetic flux calculation means.
[0009]
The transformer residual magnetic flux measuring apparatus according to the present invention also obtains an approximate function based on the absolute value of the peak point between the zero cross points of the transformer current signal after the circuit breaker is opened, and calculates by this approximate function. The voltage signal integration section detecting means terminates the integration of the voltage signal when the value to be obtained is equal to or less than a predetermined value.
[0010]
The transformer residual magnetic flux measuring apparatus according to the present invention also obtains an approximate function based on an absolute value of an average peak value between zero-cross points of the transformer current signal after the circuit breaker is opened. When the calculated value becomes equal to or less than a predetermined value, the voltage signal integration section detecting means terminates the integration of the voltage signal.
[0011]
In the transformer residual magnetic flux measuring apparatus according to the present invention, the voltage signal offset removing means calculates the center value of the voltage signal before opening of the circuit breaker as an offset amount, and the offset amount is calculated before voltage integration. Are removed from the voltage signal.
[0012]
In the transformer residual magnetic flux measuring device according to the present invention, the opening detection means obtains and stores in advance the opening time of the circuit breaker, and stores from that point in time when the circuit breaker is opened. The time at which the opened opening time has elapsed is set as the opening time.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of the first embodiment, and FIG. 2 is a waveform diagram showing signal waveforms in each part of the first embodiment. In FIG. 1, 1 is a power source, 2 is a transformer connected to the power source, 3 is connected between the power source 1 and the transformer 2, and is a circuit breaker for controlling power supply to the transformer, 4 is an open circuit of the circuit breaker 3. The opening detection means for detecting the pole detects the opening based on the contact signal 5 linked to the contact opening / closing position of the circuit breaker 3, and generates the opening signal 6 and the opening time signal 7. 8 is an instrument transformer connected to the primary side of the transformer 2, 9 is a voltage signal measuring means connected to the secondary side of the instrument transformer 8, and the voltage obtained by the instrument transformer 8 is always A / D conversion is performed at regular time intervals, and a voltage signal from the current time to a certain time, for example, 200 msec before, is stored as digital data. When the opening signal 6 is input, the voltage signal 10 before and after the opening of the circuit breaker 3 is output by stopping the storage of the voltage signal after a predetermined time has elapsed, for example, after 100 msec. In this example, digital data of 100 msec before the opening time and 100 msec after the opening time is obtained. The voltage signal measuring means 9 may have other configurations as long as voltage signals before and after opening can be obtained.
[0014]
Reference numeral 11 denotes a voltage signal offset removing unit that calculates the offset amount of the voltage signal from the voltage signal 10 before the opening time and removes the offset from the voltage signal 10. The voltage signal 10 before the opening is based on the opening time signal 7. 2 is calculated as (maximum value + minimum value) / 2, and the offset amount 101 is subtracted from the entire voltage signal 10 and the offset-removed voltage signal 12 is output. To do. Reference numeral 13 denotes voltage signal integration interval detecting means for detecting the integration interval end time from the voltage signal 12 after offset removal after the opening time based on the opening time signal 7 and is configured as follows. That is, as shown in FIG. 2B, for the voltage signal 12 after offset removal, an approximate function is created by sequentially extracting the peak points between the zero cross points after the opening time and the zero cross points.
[0015]
As shown in FIG. 2B, the zero cross points after the opening time are 102, 103, and 104 in order, and the peak points existing between the zero cross points 102 and 103 are 105, and the zero cross points 103 and 104 are also present. The peak point existing between is 106. A peak point group 107 shown on the lower side of FIG. 2B is obtained by sequentially taking out the peak points and taking their absolute values. Generally, the peak point group 107 has a property that the value decreases as time elapses from the opening time. This is because the device existing between the transformer and the circuit breaker has a parallel capacitance component, so it has energy in the parallel capacitance component at the time of interruption, and energy resonance with the reactance component of the transformer after the interruption. appear. At this time, energy loss occurs due to the hysteresis loss of the transformer, and thus the measured voltage becomes a damped oscillation waveform.
For this reason, when only the peak voltage is taken out, it is attenuated uniformly.
[0016]
Next, the obtained peak point group 107 is approximated by least squares using an attenuation function. For example, the peak function group 107 is approximated by least squares with a voltage value = K × exp (−α × time) to obtain K and α, and the approximate function 108 is created. A time at which the value of the approximation function 108 is equal to or less than a preset threshold value 109 is calculated, the time is set as the integration interval end time, and the integration interval end time signal 14 is output. Note that a time after a preset time from the time when the threshold value is 109 or less may be set as the integration interval end time.
As a simple method, the peak point group 107 is examined in order from the previous value, and a point that is lower than the preset threshold 109 is found, and the point is set in advance from the time of that point. The time after the time may be set as the integration interval end time. Reference numeral 15 denotes voltage signal integrating means for integrating the offset-removed voltage signal 12 from the beginning of the data to the integration interval end time by the integration interval end time signal 14 and outputting a voltage integration signal 16. As the integration method, a commonly used one is used.
[0017]
Reference numeral 17 denotes magnetic flux signal calculating means for calculating the offset amount of the voltage integrated signal from the voltage integrated signal 16 before the opening time, and removing the offset from the voltage integrated signal 16 and outputting the magnetic flux signal 18 and is configured as follows. ing. That is, based on the opening time signal 7, the center value of the voltage integration signal 16 before opening, that is, the offset amount 109 in FIG. 2C is calculated as (maximum value + minimum value) / 2, and the voltage The magnetic flux signal 18 is output by subtracting the offset amount 109 from the entire integration signal 16.
In this case, the integrated value is converted into a magnetic flux signal without coefficient conversion, but may be normalized by dividing the value of the magnetic flux signal 18 by the data sampling frequency.
Alternatively, the maximum amplitude A of the magnetic flux signal 18 during rated operation of the transformer may be calculated in advance and normalized by dividing the value of the magnetic flux signal 18 obtained at the time of measurement by the maximum amplitude A. A residual magnetic flux calculating means 19 reads the value of the magnetic flux signal 18 at the integration interval end time based on the integration interval end time signal 14 and outputs this value as the residual magnetic flux 20 as shown in FIG.
[0018]
In this embodiment, as described above, since the voltage integrated value at the time when the transient amplitude of the voltage signal after opening is attenuated to a predetermined value or less is read as the residual magnetic flux, the voltage integrated value is always set at the optimum reading time. As a result, the residual magnetic flux can be accurately measured.
In addition, since the center value of the voltage signal before opening is calculated and the DC offset of the voltage signal is removed before voltage integration, the monotonicity of the voltage integration signal generated due to the influence of the DC offset component superimposed on the voltage signal. As a result of no increase or monotonic decrease and the voltage integrated value converges to a constant value, the residual magnetic flux can be measured accurately.
In addition, although the above description presupposed that the power supply 1, the circuit breaker 3, and the transformer 2 are single phases, in the case of a three phase, it can be implemented by providing the above-mentioned structure for every phase. Needless to say.
[0019]
Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described. This embodiment differs only in that the configuration of the opening detection means 4 in the first embodiment shown in FIG. 1 is changed to the form described below, and the other configurations are the same as those in FIG. Illustration is omitted. That is, the opening detection means 4 according to the second embodiment obtains and stores in advance the time required for opening the circuit breaker 3, and when the opening instruction to the circuit breaker 3 is given, it is stored from that time. The opening signal 6 and the opening time signal 7 are output with the time when the required opening time has elapsed as the opening time, and the same effect as in the first embodiment can be expected.
[0020]
Embodiment 3 FIG.
Next, a third embodiment of the present invention will be described. This embodiment differs from the first embodiment shown in FIG. 1 only in that the configuration of the voltage signal integration interval detection means 13 is changed to the form described below, and the other configurations are the same as those in FIG. Therefore, illustration is abbreviate | omitted. That is, the voltage signal integration interval detection means 13 in the third embodiment sequentially extracts the average peak value between the zero cross point and the zero cross point after the opening time for the voltage signal 12 after offset removal.
Referring to FIG. 2B, the zero cross points after the opening time are 102, 103, and 104 in this order. First, an average value A of data existing between the zero cross points 102 and 103 is calculated. Next, the average value B of the data existing between the zero cross points 103 and 104 is calculated, and the average values C, D... The absolute value of the average values A, B, C, D... Calculated in this way has the property that the value decreases as time elapses from the opening time, like the peak point group 107. Therefore, by processing these values in the same manner as the voltage signal integration interval detection means 13 in the first embodiment, the same effect as in the first embodiment can be expected.
[0021]
Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described with reference to FIG. This embodiment is different from the first embodiment only in that a transformer current signal measuring means 202 is added and the configuration of the voltage signal integration interval detecting means 13 is changed to the form described below. Since the configuration is the same as in the first embodiment, only the changed part will be described.
201 is an instrument current transformer connected to the primary side in the vicinity of the transformer 2, 202 is a transformer current signal measuring means connected to the instrument current transformer 201, and the current obtained by the instrument current transformer 201 A / D conversion is performed at regular time intervals, and a transformer current signal from the current time to a certain time, for example, 200 msec before, is stored as digital data. When the opening signal 6 is input, the transformer current signal 203 before and after the opening of the circuit breaker 3 is output by stopping the storage of the transformer current signal after a certain period of time, for example, 100 msec. ing. In this example, digital data of 100 msec before the opening time and 100 msec after the opening time is obtained. The transformer current signal measuring means 202 may have another configuration as long as a transformer current signal before and after opening can be obtained.
[0022]
Reference numeral 204 denotes voltage signal integration interval detection means for detecting the integration interval end time from the transformer current signal 203 after the opening time based on the opening time signal 7 and is configured as follows. That is, as shown in FIG. 4E, for the transformer current signal 203, an approximate function is created by sequentially extracting the peak points between the zero cross point after the opening time and the zero cross point. As shown in FIG. 4E, the zero-cross points after the opening time are 302, 303, and 304 in this order, and the peak points existing between the zero-cross points 302 and 303 are 305, and the zero-cross points 303 and 304 The peak point existing between 306 is 306. A peak point group 307 shown on the lower side of FIG. 4E is obtained by sequentially taking out the peak points and taking the absolute values thereof. Like the peak point group 107, the peak point group 307 obtained in this manner has a property of decreasing in value as time elapses from the opening time. Therefore, these values are used as the voltage signal in the first embodiment. By processing in the same way as the integration interval detection means 13, the same effect as in the first embodiment can be expected.
[0023]
Embodiment 5 FIG.
Next, a fifth embodiment of the present invention will be described. This embodiment differs from the fourth embodiment shown in FIG. 3 only in that the configuration of the voltage signal integration interval detection means 204 is changed as described below, and the other configurations are the same as those in FIG. Therefore, illustration is abbreviate | omitted. That is, the voltage signal integration interval detection means 204 in the fifth embodiment sequentially extracts the average peak value between the zero cross point and the zero cross point after the opening time for the transformer current signal 203.
If it demonstrates using FIG.4 (e), the zero crossing point after opening time is 302, 303, 304 in order, First, the average value A of the data which exist between the zero crossing points 302 and 303 is calculated. Next, the average value B of data existing between the zero cross points 303 and 304 is calculated, and the average values C, D... The absolute value of the average values A, B, C, D... Calculated in this way has the property that the value decreases as time elapses from the opening time, like the peak point group 307. Therefore, by processing these values in the same manner as the voltage signal integration interval detection means 204 in the fourth embodiment, the same effect as in the fourth embodiment can be expected.
[0024]
【The invention's effect】
A transformer residual magnetic flux measuring apparatus according to the present invention stores an opening detection means for detecting an opening time of a circuit breaker connected to a power supply circuit of a transformer, and stores a voltage signal of the power supply circuit for a predetermined time. Voltage signal measuring means adapted to measure the voltage signal of the feeder circuit before and after opening of the circuit breaker, and calculating an offset amount of the voltage signal before opening of the circuit breaker, Voltage signal offset removing means for removing the offset from the voltage signal, voltage signal integration interval detecting means for setting the time when the transient vibration of the voltage signal after opening of the circuit breaker is attenuated to a predetermined value or less as the end of integration, Voltage signal integrating means for integrating the voltage signal, magnetic flux signal calculating means for obtaining a magnetic flux signal by removing the offset of the voltage integrated signal, and residual magnetic flux calculating means for calculating a residual magnetic flux value from the magnetic flux signal As a result, the integrated voltage value can always be obtained at the optimal reading time, and the monotonous increase or decrease of the integrated voltage signal is eliminated, and the integrated voltage value converges to a constant value. The residual magnetic flux can be measured accurately.
[0025]
The transformer residual magnetic flux measuring apparatus according to the present invention is also a value calculated by an approximate function obtained based on an absolute value of a peak point between zero-cross points of an offset-removed voltage signal after opening of the circuit breaker. When the value calculated by the approximation function calculated based on the absolute value of the average peak value between zero-cross points of the voltage signal after offset removal becomes less than the predetermined value, Since the integration is terminated, a voltage integrated value can always be obtained at the optimum reading time, and as a result, the residual magnetic flux can be accurately measured.
[0026]
The residual magnetic flux measuring device for a transformer according to the present invention further includes an opening detection means for detecting an opening time of a circuit breaker connected to the power supply circuit of the transformer, and stores a voltage signal of the power supply circuit for a predetermined time. And a voltage signal measuring means adapted to measure the voltage signal of the feeder circuit before and after opening of the circuit breaker and a transformer current signal of the transformer for a predetermined time. A transformer current signal measuring means capable of measuring a transformer current signal before and after opening of the circuit breaker, and calculating an offset amount of the voltage signal before opening of the circuit breaker. Voltage signal offset removal means for removing offset from the voltage signal integration interval detection means for setting the time when the transient vibration of the transformer current signal after opening of the circuit breaker is attenuated below a predetermined value as the end of integration; A voltage signal integrating means for integrating the voltage signal; a magnetic flux signal calculating means for obtaining a magnetic flux signal by removing an offset of the voltage integrated signal; and a residual magnetic flux calculating means for calculating a residual magnetic flux value from the magnetic flux signal Therefore, the integrated voltage value can always be obtained at the optimum reading time, and the monotonic increase or decrease of the voltage integral signal is eliminated, and the integrated voltage value converges to a constant value. Can be measured.
[0027]
The transformer residual magnetic flux measuring apparatus according to the present invention also obtains an approximate function based on the absolute value of the peak point between the zero cross points of the transformer current signal after the circuit breaker is opened, and calculates by this approximate function. The approximate function is obtained when the measured value is less than the predetermined value or based on the absolute value of the average peak value between the zero cross points of the transformer current signal, and the value calculated by this approximate function is less than the predetermined value. Since the integration of the voltage signal is terminated, the integrated voltage value can always be obtained at the optimum reading time, and as a result, the residual magnetic flux can be measured accurately.
[0028]
In the transformer residual magnetic flux measuring device according to the present invention, the center value of the voltage signal before opening of the circuit breaker is calculated as an offset amount, and the offset is removed from the voltage signal before voltage integration. As a result of the monotonic increase or decrease of the voltage integration signal disappearing and the voltage integration value converging to a constant value, the residual magnetic flux can be accurately measured.
[0029]
In the transformer residual magnetic flux measuring device according to the present invention, the opening detection means obtains and stores in advance the opening time of the circuit breaker, and stores from that point in time when the circuit breaker is opened. Since the time when the opened opening time has elapsed is set as the opening time, the residual magnetic flux can be measured accurately as a result.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a first embodiment of the present invention.
FIG. 2 is a waveform diagram showing signal waveforms at various parts in the first embodiment.
FIG. 3 is a circuit diagram showing a configuration of a fourth embodiment of the present invention.
FIG. 4 is a waveform diagram showing signal waveforms at various parts in the fourth embodiment.
FIG. 5 shows a magnetic flux waveform for explaining a conventional residual magnetic flux measuring method.
[Explanation of symbols]
2 transformer, 3 circuit breaker, 4 open-circuit detection means,
9 voltage signal measuring means, 11 voltage signal offset removing means,
13, 204 Voltage signal integration interval detection means, 15 Voltage signal integration means,
17 magnetic flux signal calculating means, 19 residual magnetic flux calculating means,
202 Transformer current signal measuring means.

Claims (8)

An opening detection means for detecting an opening time of a circuit breaker connected to a power supply circuit of the transformer, and a voltage signal of the power supply circuit are stored for a predetermined time, and the power supply before and after the circuit breaker is opened. A voltage signal measuring means adapted to measure a voltage signal of the circuit; a voltage signal offset removing means for calculating an offset amount of the voltage signal before opening the breaker and removing the offset from the voltage signal; A voltage signal integration section detecting means for setting the end of integration when the transient vibration of the voltage signal after opening of the circuit breaker is attenuated to a predetermined value or less, a voltage signal integrating means for integrating the voltage signal, and a voltage transformer comprising a magnetic flux signal calculation means for obtaining a magnetic flux signal by removing the offset before opening of the circuit breaker of the integrated signal, and a residual magnetic flux calculation means for calculating the residual magnetic flux value from the magnetic flux signal Residual magnetic flux measurement apparatus. The voltage signal integration interval detecting means obtains an approximate function based on an absolute value of a peak point between zero-cross points of the voltage signal after offset removal after opening of the circuit breaker, and a value calculated by the approximate function is a predetermined value. 2. The residual magnetic flux measuring apparatus for a transformer according to claim 1, wherein the integration of the voltage signal is terminated when the value becomes equal to or less than the value. The voltage signal integration interval detecting means obtains an approximate function based on an absolute value of an average peak value between zero-cross points of the voltage signal after offset removal after opening of the circuit breaker, and a value calculated by the approximate function is 2. The residual magnetic flux measuring apparatus for a transformer according to claim 1, wherein the integration of the voltage signal is terminated when the voltage becomes equal to or less than a predetermined value. An opening detection means for detecting an opening time of a circuit breaker connected to a power supply circuit of the transformer, and a voltage signal of the power supply circuit are stored for a predetermined time, and the power supply before and after the circuit breaker is opened. Voltage signal measuring means adapted to measure the voltage signal of the circuit, and the transformer current signal of the transformer is stored for a predetermined time, and the transformer current signal before and after opening of the circuit breaker is measured. Transformer current signal measuring means, voltage signal offset removing means for calculating an offset amount of the voltage signal before opening the circuit breaker and removing the offset from the voltage signal, and the circuit breaker Voltage signal integration section detecting means for ending the integration when the transient vibration of the transformer current signal after the opening of the circuit is attenuated to a predetermined value or less, voltage signal integrating means for integrating the voltage signal, voltage And the magnetic flux signal calculation means for obtaining a magnetic flux signal by removing the offset before opening of the circuit breaker of the partial signals, the residual magnetic flux measurement of the transformer with a residual magnetic flux calculation means for calculating the residual magnetic flux value from the magnetic flux signal apparatus. The voltage signal integration interval detection means obtains an approximate function based on the absolute value of the peak point between the zero cross points of the transformer current signal after opening the breaker, and the value calculated by the approximate function is a predetermined value. 5. The residual magnetic flux measuring device for a transformer according to claim 4, wherein the integration of the voltage signal is terminated when the following occurs. The voltage signal integration interval detecting means obtains an approximate function based on an absolute value of an average peak value between zero-cross points of the transformer current signal after the circuit breaker is opened, and a value calculated by the approximate function is a predetermined value. 5. The residual magnetic flux measuring device for a transformer according to claim 4, wherein the integration of the voltage signal is terminated when the value becomes lower than the value. 2. The voltage signal offset removing means calculates a center value of a voltage signal before opening of the circuit breaker as an offset amount, and removes the offset from the voltage signal before voltage integration. The residual magnetic flux measuring apparatus for a transformer according to any one of claims 6 to 7. The opening detection means obtains and stores the opening time of the circuit breaker in advance, and at the time of opening instruction of the circuit breaker, the time when the opening time stored from that time has passed is set as the opening time. The transformer residual magnetic flux measuring apparatus according to any one of claims 1 to 7, wherein the apparatus is configured as described above.

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