JP2011216630A - Method and device for controlling density of residual magnetic fluxes in transformer iron core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the density of residual magnetic fluxes in a transformer iron core to a desired value.SOLUTION: The method includes: an initializing step (S1) of applying a DC voltage to a transformer to bring it into a positive saturated state; a saturation energy calculating step (S2-S5) of applying a negative DC voltage, in a direction reverse to the initializing step, to the transformer brought into the saturated state by executing the initializing step to bring it into a saturated state, then interrupting the application of the DC voltage, and obtaining a first integrated value V1 obtained by integrating a voltage value Vi of the DC voltage according to the energy for saturation required from start of application of the DC voltage to interruption; and a step (S7-S10) of applying a positive DC voltage which is the same as the DC voltage applied in the initializing step to the transformer by the amount corresponding to energy which is one half the energy V1 obtained in the saturation energy calculating step. As a result, the density of residual magnetic fluxes is reduced to zero. The density of residual magnetic fluxes can be optionally set by setting energy applied by a positive DC voltage to X% of V1.

Description

  The present invention relates to a method and apparatus for controlling residual magnetic flux density of a transformer core, and relates to a technique for controlling the residual magnetic flux density of an iron core of a distribution transformer such as a pole transformer.

  Overhead distribution lines that distribute power from distribution facilities such as substations to homes and factories are equipped with pole transformers. This pole transformer transforms AC 6.6 [kV] high voltage power applied to the high voltage distribution line into 100 [V] and 200 [V] low voltage power that can be used in homes and factories (transformation). To do. There are various types of transformer structures, including such pole transformers, but all have a basic configuration in which a coil is attached to an iron core. And since an iron core has a hysteresis characteristic, in order to calculate the magnetic characteristic of a transformer, it is necessary to consider the influence of residual magnetic flux.

  Demagnetization can be performed by setting the residual magnetic flux to zero. In conventional demagnetization, AC demagnetization is used in which an alternating magnetic flux (AC voltage) is applied to the transformer until it is slightly overexcited, and the magnitude of the magnetic flux (voltage) is gradually reduced. In particular, the demagnetization of the distribution transformer, which is the subject of the present invention, is to apply an alternating voltage higher than the rated voltage for the purpose of preventing an inrush current, and a worker manually applies a voltage using a slidac or the like. The value is gradually lowered to finally become 0. In addition, the prior art document disclosed about this demagnetizing method was not found.

  However, when such a general demagnetization method is used, the residual magnetic flux can be surely reduced, but a voltage higher than the rated voltage is required, and the apparatus itself becomes large. Therefore, in order to perform failure determination processing such as a short circuit between windings after going out into the city, actually applying voltage to the pole transformer etc. and demagnetizing, development of a compact device is essential, There is a problem that requires the development of a degaussing device suitable for it.

  Furthermore, as described above, the demagnetization of the transformer for preventing the magnetizing inrush current is performed using an AC voltage, but since a high-voltage AC voltage higher than the rated voltage is applied, the work place is connected to the power source concerned. Since it is limited to a certain area and is attenuated by manual operation, not only is the work complicated, but also it tends to attenuate more slowly than necessary in order to reliably degauss, and it takes work time and efficiency However, there is also a problem that it is desired to develop a compact device that automatically demagnetizes the transformer in a short time.

  In addition, various methods have been proposed to reduce the residual magnetic flux density to 0, such as demagnetization. However, attention has been paid to controlling the residual magnetic flux density to a desired value. There was no solution for that.

  In order to solve the above-mentioned problems, a residual magnetic flux density control device according to the present invention includes (1) initial processing means for applying a DC voltage to a transformer to make it positive or negative saturation state, and the transformer in saturation state. DC voltage applying means for applying a DC voltage for saturation in the reverse direction to the transformer, saturation detecting means for detecting that the iron core of the transformer is saturated, and saturation by the initial processing means Until the saturation is detected by the saturation detecting means, a DC voltage opposite to that of the initial processing means is applied to the transformer, and when the iron core is saturated, the transformer is immediately shut off. A saturation energy calculation means for obtaining the energy required for saturation from the start of voltage application to the cutoff and a direct current voltage in the same direction as the initial processing means are applied, and the energy applied to the transformer is monitored at the time of application. Energy was constructed and a control means for interrupting the application of the DC voltage having the same direction when the has become the value set for the energy to saturate obtained by the saturation energy calculating means.

  In the embodiment, each means described above is realized as one function (function / program for executing a predetermined processing step of the flowchart) of the control unit 8 (calculation unit 2). In the embodiment, the initial processing means has a function of performing a process of applying a DC voltage for a certain period of time, and is realized by, for example, a function of executing the processing step S1. The fixed time is set to a sufficient time so as to saturate in any case of residual magnetic flux density that can be taken under normal use conditions. Of course, if the length is too long, the measurement time becomes long and the voltage is applied unnecessarily to consume energy, so the length is set appropriately. Further, in order to adopt a simple configuration, in the embodiment, the voltage is applied for a certain period of time. However, it may be monitored whether or not it is saturated, and application of the voltage may be stopped when saturated. In the embodiment, the saturation detection unit monitors the current value of the excitation current, and determines that the saturation occurs when it suddenly increases (processing step S4). However, other methods may be used. In the embodiment, the saturation energy calculation unit is realized by a function of executing the processing step S3. In the embodiment, the control means is realized by a function of executing the processing steps S7 to S10.

  A positive or negative saturation state is set, and the energy required until the opposite saturation state is obtained by the saturation energy calculation means. When a DC voltage is applied in the same direction as the DC voltage applied during the initial processing by the determined energy, the original saturated state after the initial processing is restored. In addition, if the application of the DC voltage is interrupted when half of the calculated energy is applied, the magnetic field is applied at the midpoint between the positive or negative maximum residual magnetic flux density state and the other maximum residual magnetic flux density state. Since the application is stopped, the residual magnetic flux density becomes zero. Similarly, by setting the amount of energy to be applied to a predetermined ratio of the obtained energy, the residual magnetic flux density becomes a value corresponding to the predetermined ratio. Therefore, the residual magnetic flux density can be controlled.

  Since the residual magnetic flux density is controlled using the DC voltage, it can be realized with a simple configuration. Therefore, even if it is excellent in carrying and it is a processing target scattered in towns, such as a pole transformer, it can be easily made into a desired residual magnetic flux density.

  (2) It is preferable that the saturation energy calculation means obtains an integral value of the voltage value of the DC voltage. This is preferable because the arithmetic processing is simplified.

  (3) The said control means is good to perform the said interruption | blocking, when the monitored energy becomes half of the said energy to be saturated calculated | required by the said saturation energy calculation means. In this way, the residual magnetic flux density can be made zero. Moreover, it is preferable that the demagnetization process is completed only by applying the DC voltage three times in total.

  (4) The saturation detection means may be configured to determine the presence or absence of saturation based on a current value of an exciting current that flows when a DC voltage is applied to the transformer by the DC voltage application means. When a DC voltage is applied, the current value of the exciting current gradually increases as time passes, but the current value suddenly increases when the saturation state is reached. Therefore, the presence or absence of saturation can be detected based on the change.

  (5) The DC voltage power source may be a battery. In this way, the entire apparatus is compact and convenient to carry. Considering the winding resistance and the number of turns, most current distribution transformers can saturate the magnetic flux density of the iron core with a DC power supply of about several volts. Therefore, there is no problem because the residual magnetic flux density can be controlled by a DC voltage in which several batteries are connected in series.

  (6) The control method according to the present invention includes an initial process for applying a DC voltage to a transformer to make it a positive or negative saturation state; Saturation energy calculation processing to obtain the energy required to saturate from the start of application of the DC voltage to the cutoff after the application of the DC voltage is reversed by applying a DC voltage in the opposite direction to the process , Executing a process of applying, to the transformer, a DC voltage in the same direction as the DC voltage applied in the initial process by the amount of energy set in the saturation energy calculation process.

  (7) The energy to be saturated may be obtained by integrating the voltage value of the DC voltage.

  (8) The ratio is preferably 50%. Thereby, demagnetization can be performed.

  In the present invention, the residual magnetic flux density of the iron core of the transformer can be controlled with a simple configuration.

It is a figure which shows suitable one Embodiment of the residual magnetic flux density control apparatus which concerns on this invention. It is a figure explaining the subject of this invention. It is a figure which shows an example of a hysteresis curve. It is a figure explaining the function of saturation detection. It is a flowchart which shows the function of a calculating part. It is a figure which shows the function and operation | movement principle of a calculating part. It is a figure explaining the effect of this invention. It is a figure which shows the function and operation | movement principle of a calculating part.

  FIG. 1 shows a schematic configuration of a residual magnetic flux density control device according to the present invention. As shown in FIG. 1, the probe 1 which is a measurement terminal connected to the terminal of each phase of a transformer is provided. In order to connect to each phase, three probes 1 are prepared in this embodiment. Each probe 1 is connected to a control unit 8 via a measurement circuit 7 that measures voltage and current. Further, the residual magnetic flux density control device includes an input unit 4 as a man-machine interface, a notification unit 5, and a power supply unit 6 for operating each unit.

  The input unit 4 includes an operation switch for instructing power ON / OFF, setting various modes, starting control, and the like. The notification unit 5 includes a voice (sound) output unit such as a buzzer and a visual output unit such as a lamp / display, and notifies the operation result.

  The power supply unit 6 uses a battery in this embodiment. That is, it is a DC power supply, and is a power supply voltage for driving the CPU and various electronic devices. Further, as will be described later, it is also used as a power source for controlling residual magnetic flux density such as demagnetization using a DC voltage. Specifically, four batteries having a nominal voltage of 1.2 to 1.5 [V] (for example, a nickel hydride battery of 1.2 [V]) are connected in series, and between the terminals of all the batteries connected in series. The voltage is 4.8 to 6 [V], and the output is about 4 to 5 [W]. Of course, the number connected in series is arbitrary. Further, it is not hindered to continuously extend the life by connecting the batteries in parallel. In addition, in order to stabilize the output voltage value, as will be described later, a stabilization circuit (regulator) is connected to the output of the battery and output through the stabilization circuit to output a predetermined DC voltage of about 3 [V]. Is output.

  The measurement circuit 7 measures electrical characteristics such as voltage across the terminals of the transformer and exciting current, and the measurement result is given to the control unit 8 (calculation unit 2) to control operation in each unit. This is used for determining the end of processing.

  The control unit 8 controls the residual magnetic flux in the iron core of the transformer. That is, for example, in the failure determination device disclosed in Japanese Patent Laid-Open No. 7-94341, alternating current voltages having different frequencies are sequentially applied, and the excitation current of the transformer when the alternating voltages having different frequencies are applied is measured. A technique is disclosed in which a predetermined calculation process is performed based on the measured excitation current value to determine the presence or absence of a short circuit. Such a determination can be made based on whether the value of the excitation current increases (healthy / normal) or decreases (short circuit) as the frequency increases. The first-order differentiation of the curve, and as a result of the differentiation, determination can be made depending on whether the curve is increasing or decreasing.

  In addition, without first-order differentiation, AC voltages (sine waves) with different frequencies (for example, 1 kHz and 3 kHz) are switched and output, excitation currents at the respective frequencies are obtained, and winding is performed based on the magnitude relationship. The presence or absence of a short circuit between lines can also be determined. In this case, when the excitation current at a high frequency is larger, it tends to increase, so it is normal, and when the excitation current at a higher frequency is smaller, it tends to decrease, so a short circuit between windings. Can be determined. However, if an attempt is made to determine a failure by the above arithmetic processing, it may not be determined correctly. This is influenced by the residual magnetic flux in the transformer core. That is, there is a residual magnetic flux in the iron core of a normally used transformer, and the magnitude and direction of the magnetic field are not constant. The reason is that the residual magnetic flux of the iron core is influenced by the voltage and polarity at the time of interruption immediately before that.

  Therefore, if the residual magnetic flux is different, even if the same voltage is applied, the value of the exciting current that flows along with the application of the voltage is also different. Therefore, as shown in FIG. 2, the measurement result changes every time measurement is performed. . As a result, there is a risk that correct determination cannot be made. Therefore, in the present embodiment, the control unit 8 can make the initial state at the time of determination constant by making the residual magnetic flux density a desired value, and can perform stable determination. Demagnetization can be performed by setting the residual magnetic flux density to zero. Of course, the residual magnetic flux density control device of the present embodiment can be used not only as a pre-processing for failure determination as described above but also in various fields.

  And the residual magnetic flux density control apparatus of this embodiment controls the residual magnetic flux to a desired value using the DC voltage of the power supply unit 6. Considering the winding resistance and the number of turns, most of current distribution transformers can saturate the magnetic flux density of the iron core with a DC power supply of about several volts. If this is utilized, the residual magnetic flux density can be controlled with a small voltage, so that the residual magnetic flux density control device becomes compact and portable.

  As is well known, the magnetization curve (BH curve) of the ferromagnetic material used for the iron core has a characteristic like a hysteresis curve as shown in FIG. 3, and increases the magnetic field strength H [A / m]. As the value is increased, the magnetic flux density B [T] is saturated. Thereafter, even if the strength of the magnetic field is returned to 0, the magnetic flux density does not become 0, but a residual magnetic flux density of a predetermined value. As described above, the residual magnetic flux density differs depending on the strength and direction (positive / negative) of the magnetic field when the magnetic field is applied immediately before, and as shown in FIG. 3, the magnetic field strength is reduced to 0 once saturated. In this case, the residual magnetic flux density is the largest and the maximum magnetic flux density Bm. When a DC voltage is applied, a magnetic field corresponding to the voltage value is applied. Therefore, the iron core can be saturated by setting the voltage value of the DC voltage to an appropriate value (about several volts).

  In order to achieve magnetic saturation in this way, the calculation unit 2 applies a DC voltage output from the power supply unit 6 to the terminal of the transformer via the probe 1. When a DC voltage is continuously applied to the transformer, the iron core of the transformer reaches a saturation region, and the magnetic flux remains in the iron core as a residual magnetic flux. That is, since silicon steel plates and amorphous materials have a large magnetic permeability, the self-inductance of a coil made using these as iron cores has a large value. Therefore, when a DC power source is applied to this coil, the excitation current gradually increases over time as shown in FIG. When a certain current value (magnetomotive force) is reached, the apparent permeability decreases and the self-inductance also decreases, so the excitation current almost instantaneously reaches a value determined by the winding resistance and the power supply voltage. In other words, the exciting current is monitored, and when the value increases rapidly, it can be determined that the iron core is saturated.

  In the case of the same transformer, the difference in residual magnetic flux density before and after applying the external magnetic field increases as the energy applied when the external magnetic field (H) is applied in a state where magnetic saturation is not performed increases. Become. Therefore, for example, when the energy added from the positive saturation state to the negative saturation state is obtained and half of the energy is applied in the reverse direction (positive direction), the residual magnetic flux becomes zero. In other words, if the absolute value of energy required to change from the positive maximum magnetic flux density Bm to the negative maximum magnetic flux density −Bm is E, an external magnetic field is applied in the positive direction by the energy (E), When the external magnetic field is set to 0, the maximum positive magnetic flux density Bm is obtained again. Therefore, when the external magnetic field is reduced to 0 after half (50%) energy (0.5E) is applied, “magnetic flux density = 0”, which is an intermediate point between “−Bm” and “Bm”, and demagnetization is completed. To do.

  Specifically, the control of the residual magnetic flux density based on the energy applied to the iron core is performed by the calculation unit (CPU) 2 in the control unit 8 executing the following algorithm shown in FIG. First, the calculating part 2 makes the iron core of a transformer a positive saturation state (S1). Specifically, the iron core is saturated by applying the voltage (positive DC voltage) output from the power supply unit 6 as it is to the transformer for a certain period of time. That is, FIG. 6 shows an example of the hysteresis curve (BH characteristic) of the iron core. And the residual magnetic flux at the time of applying such a positive direct current voltage has the magnitude | size and direction of a magnetic field as above-mentioned vary. Therefore, the calculation unit 2 applies a DC voltage for a sufficient time (for example, 1 second) to reliably saturate (see (1) in FIG. 6), and then shuts off the power supply. As a result, the magnetic field H applied to the iron core is also zero, and the maximum residual magnetic flux Bm is obtained. In this way, once saturated in the positive direction, the variation in the magnitude of the residual magnetic flux and the direction of the magnetic field based on the immediately preceding use state is eliminated, and the same initial state can be obtained.

  For example, when a short circuit occurs, a large current flows with the application of the DC voltage, and it is not preferable that the state continues even for one second. Therefore, when this process is executed, the excitation current is monitored, and if a preset stop condition such as a current value increases rapidly or exceeds a predetermined reference value is satisfied, it is cut off. Good.

  In this embodiment, a positive DC voltage is applied to achieve a positive saturation state. However, a negative DC voltage may be first applied to obtain a negative saturation state. In that case, the direction of the DC voltage applied in each processing step in the following description may be reversed. The function of executing this processing step S1 corresponds to the initial processing means.

  Next, the calculating part 2 applies a negative DC voltage to a transformer, and makes an iron core into a negative saturation state. Here, instead of applying a fixed time as in processing step S1, the excitation current is monitored and a predetermined DC voltage is applied until saturation occurs. The computing unit 2 resets the first integrated voltage value V1, which is an integrated value of the DC voltage applied to the transformer via the probe 1, and starts applying a negative DC voltage (S2). Since this first integrated voltage value V1 is stored in the buffer memory 3, the value of the buffer memory 3 is set to zero.

  The calculation unit 2 acquires the current voltage value Vi at each sampling time, reads the first integrated voltage value V1 stored in the buffer memory 3, adds the current voltage value Vi, and obtains a new first integrated voltage. The value V1 is obtained and overwritten on the buffer memory 3 (S3). That is, an external magnetic field is applied by applying a negative DC voltage, and the energy applied to the transformer (iron core) at that time can be obtained by time-integrating the product of the voltage value and the current value. In the present embodiment, the current value of the voltage value is acquired at regular intervals at the same sampling time both when applying a negative DC voltage and when applying a positive DC voltage described later. Acquisition was omitted. Of course, if the current value of the voltage value acquired this time is not captured at regular intervals, it is added to the period by multiplying the current value of the voltage value acquired this time by the time from acquisition of the current value of the previous time to acquisition of the current value of the current time. A value corresponding to energy is obtained. The voltage value Vi is an absolute value.

  Further, in order to obtain more accurately applied energy, it is preferable to integrate the current value of the excitation current consumed for magnetization, but as shown in FIG. In the region where the current value becomes almost zero and the current value increases due to saturation, the amount of power consumed by the winding has a greater influence than the power required for magnetization that saturates the iron core. Therefore, if the current value is integrated, the accurate energy required for magnetic saturation can no longer be obtained. Therefore, in this embodiment, the current value is not integrated. If the voltage is integrated, the energy required for saturation of the iron core can be calculated without significantly affecting the rise of the current. In the present embodiment, since a battery is used for the power supply unit 6, the voltage value gradually decreases. The function of executing the processing step S3 for integrating the voltages corresponds to the saturation energy calculating means.

  Next, the calculation unit 2 determines whether or not the excitation current has increased abruptly (S4). The function of executing the processing step for making such a determination corresponds to the saturation detection means. In the section where the excitation current is slightly increased in the almost zero state (section A in FIG. 4), it is in an unsaturated state. While the DC voltage is continuously applied, the excitation current is continuously monitored and the voltage value is integrated every sampling time.

  If the exciting current increases rapidly ("X" in FIG. 4), the branch determination in processing step S4 becomes Yes, and it can be estimated that the iron core is in a negative saturation state (see (3) in FIG. 6). For this determination, for example, a threshold value (for example, 5 [A]) is set in advance, and if the current value of the excitation current exceeds the threshold value, the branch determination in S4 can be Yes. Further, the value of the previous excitation current is stored, and when the difference from the current excitation current becomes a certain threshold value or more, it can be determined that it has increased rapidly.

  If the excitation current increases rapidly, the calculation unit 2 shuts off the power supply (S5). The interruption of the power supply is not required if no negative DC voltage is finally applied to the transformer and no exciting current flows through the winding. When the application of the DC voltage is interrupted when the excitation current increases rapidly in this way, a counter electromotive force is generated, and then the voltage gradually decreases and returns to 0 (see (4) in FIG. 6). When the counter electromotive force becomes zero, a negative constant residual magnetic flux (negative maximum magnetic flux density -Bm) is generated in the iron core as shown in FIG. The arithmetic unit 2 waits for the electromotive force to become 0 in this way (S6).

  Next, the computing unit 2 resets the second integrated voltage value V2, which is an integrated value of the voltage value of the positive DC voltage applied to the transformer via the probe 1, and starts applying a positive DC voltage ( S7). Since the second integrated voltage value V2 is stored in the buffer memory 3, the value of the buffer memory 3 is set to zero.

  The calculation unit 2 acquires the current voltage value Vi at each sampling time, reads the second integrated voltage value V2 stored in the buffer memory 3, adds the current voltage value Vi, and obtains a new second integrated voltage. The value V2 is obtained and overwritten on the buffer memory 3 (S8). And the calculating part 2 judges whether the calculated | required 2nd integrated voltage value V2 is a half of the 1st integrated voltage value V1 corresponding to the energy required when making it into a negative saturation state (S9). .

  If it becomes Yes in S9 (see (5) in FIG. 6), the calculation unit 2 shuts off the power supply (S10). The interruption of the power supply is not required if no negative DC voltage is finally applied to the transformer and no exciting current flows through the winding. A counter electromotive force is generated by this voltage cutoff, and then the voltage gradually decreases and returns to 0 (see (6) in FIG. 6). Since the energy applied to the iron core of the transformer before the voltage is cut off in the processing step S10 is half of the energy required to change from the positive saturation state to the negative saturation state, the counter electromotive force becomes zero. The residual magnetic flux density at this time becomes 0, and the degaussing process is completed.

  As in the present embodiment, demagnetization is performed first, and then the frequency-excitation current characteristics are measured. As shown in FIG. 7, even if a plurality of measurements are performed on the same transformer, almost the same value ( Characteristic). On the other hand, as described above, when the measurement is performed without demagnetization, the measurement results are different for each measurement as shown in FIG. The effect of degaussing can be confirmed by comparing FIG. 2 and FIG. As a result, high-performance detection / determination can be performed when a failure determination is made on the presence / absence of a short circuit between windings based on the frequency-excitation current characteristics after degaussing with this apparatus.

  In the embodiment described above, the residual magnetic flux density is controlled to be zero and the demagnetization is performed. However, the present invention is not limited to this, and the residual magnetic flux density can be set to an arbitrary value. As an example, an external magnetic field is applied in a positive direction from a negative saturation state, and 75% energy (0.75E, V2 = 0.75V1) is applied, so that half the maximum positive magnetic flux density (Bm / 2) (see FIG. 8A), and by adding 25% energy (0.25E, V2 = 0.25V1), half of the negative maximum magnetic flux density (-Bm / 2) (See FIG. 8B).

That is, by changing the coefficient to be multiplied by V1 in the branch determination in the processing step S9, the value of V2 that satisfies the branch determination condition of the step changes, and the final residual magnetic flux density can be controlled accordingly. That is, when the energy applied when the positive DC voltage is applied in processing step S7 is X% of the energy (first integrated voltage value) added when the positive saturation state is changed to the negative saturation state. Processing step S9
V2 = (X / 100) V1
It becomes.
And the residual magnetic flux density in that case is
When X is 50% or more,
Bm / [100 / {2 (X-50)}]
= 2 (X-50) Bm / 100
If X is less than 50%,
-Bm / {100 / (2X)}
= (2X) Bm / 100
Become

DESCRIPTION OF SYMBOLS 1 Probe 2 Calculation part 3 Buffer memory 4 Input part 5 Notification part 6 Power supply part 7 Measurement circuit 8 Control part

Claims (8)

Initial processing means for applying a DC voltage to the transformer to bring it into a positive or negative saturation state;
DC voltage application means for applying a DC voltage to the saturated transformer in a reverse direction to the saturated state,
Saturation detecting means for detecting that the iron core of the transformer is saturated;
A DC voltage opposite to that of the initial processing means is applied to the transformer saturated by the initial processing means until saturation is detected by the saturation detection means, and the iron core is saturated. Saturation energy calculation means for immediately cutting off and obtaining the energy required for saturation from the start of application of the DC voltage to the cutoff.
Apply a DC voltage in the same direction as the initial processing means, monitor the energy applied to the transformer at the time of application, and the energy is a value set for the saturation energy obtained by the saturation energy calculation means Control means for cutting off the application of the DC voltage in the same direction when
A residual magnetic flux density control device for a transformer core, comprising:   2. The residual magnetic flux density control device for a transformer core according to claim 1, wherein the saturation energy calculation means calculates an integral value of a voltage value of the DC voltage.   3. The transformer core according to claim 1, wherein the control unit performs the shut-off when the monitored energy is half of the saturation energy obtained by the saturation energy calculation unit. 4. Residual magnetic flux density control device.   2. The saturation detection unit is configured to determine the presence or absence of saturation based on a current value of an exciting current that flows when a DC voltage is applied to the transformer by the DC voltage application unit. The residual magnetic flux density control apparatus of the transformer core using the direct current | flow in any one of 3.   The residual magnetic flux density control device for a transformer core according to any one of claims 1 to 4, wherein the DC voltage power source is a battery. Initial treatment to apply DC voltage to the transformer to make it positive or negative saturation,
Applying a DC voltage in the opposite direction to the initial process to the transformer that has been saturated by executing the initial process, and then saturating, then applying the DC voltage is interrupted and applying the DC voltage Saturation energy calculation processing for obtaining energy to be saturated from the start until the shutoff,
A process of applying a DC voltage in the same direction as the DC voltage applied in the initial process by an amount of energy set in relation to the energy obtained in the saturation energy calculation process,
A method for controlling residual magnetic flux density of a transformer core.   The method of controlling residual magnetic flux density of a transformer core according to claim 6, wherein the energy to be saturated is obtained by integrating voltage values of the DC voltage.   The said ratio is 50%, The residual magnetic flux density control method of the transformer core of Claim 6 or 7 characterized by the above-mentioned.

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