JP5560432B2 - Transformer failure judgment device - Google Patents

Description

  The present invention relates to a transformer failure determination device, for example, a failure determination device that detects the presence or absence of a short-circuit between windings in a distribution transformer such as a pole transformer, and other failure detection.

  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. When such a pole transformer fails, an abnormal voltage or current is generated, and the power supply is cut off by the protection circuit.

  Therefore, after narrowing down the scope of the accident as a step to identify the point of failure when a distribution line accident occurs, the fault judgment of each transformer is performed using a transformer fault judgment device (trans checker). It is common to check the soundness one by one and identify the accident point.

  The principle of operation of this type of conventional transformer failure determiner is as follows. First, a transformer that is disconnected internally has an infinite or very close electrical resistance at the terminals. In order to detect the failure of the transformer in such a state, it is possible to apply a DC voltage and measure the winding resistance.

  In addition, among the failures in the above-mentioned pole transformer, a short circuit between the windings that occurred inside the transformer (rare short: layer short, turn short: turn short) is a closed circuit inside the transformer. . When an AC voltage is applied to the transformer in such a state, a large current flows even in a no-load state. Using this principle, it is possible to detect a short-circuit between windings such as a rare short. As an example, there is a technique in which an AC voltage in a frequency range of 200 to 600 Hz is applied to the secondary side of a transformer, and the excitation current is compared with a predetermined fixed threshold value to determine the presence or absence of a short circuit between windings. Known (for example, Patent Document 1). This utilizes the characteristic that the excitation current increases when a short circuit occurs between the windings. In particular, a transformer having a smaller excitation current than the threshold value in the frequency range of 200 to 600 Hz, This is a technique for determining a larger transformer as a transformer in which windings are short-circuited.

  Most of the pole transformer failures that blow the high-voltage cutout fuses in power distribution facilities are accompanied by shorts between the windings. Therefore, in the initial judgment, if an abnormal transformer is judged to be normal or a normal transformer is mistakenly judged to be abnormal, it will affect the identification of the later failure point, causing problems in safety and efficiency in field work. End up. Therefore, the initial determination by the transformer failure determination device as described above plays a very important role.

  Also, when reusing a removed transformer, it is necessary to determine its soundness easily and accurately. Therefore, the quality determination of the removed product by the transformer failure determination device is also as important as the determination at the time of the accident.

  The conventional transformer failure determination device disclosed in Patent Document 1 and the like is based on the principle of detecting a disconnection of a transformer and a short circuit between windings with a preset current magnitude. In the case of a transformer having a characteristic deviating from the above, there is a possibility that it is determined as a failure. One example is shown in FIG. Even if the transformer with a large capacity is healthy, the excitation current is large, and the current value may be the same as the excitation current when a transformer with a small capacity is rarely short-circuited. Up to this point, until now, the characteristics of the targeted distribution transformers were mostly within a certain range, regardless of the manufacturer or generation, so there were few problems.

  However, in recent years, transformers with various characteristics have emerged as a result of increasing the efficiency of distribution transformers and increasing the number of items by manufacturer. For example, in recent years, high efficiency transformers such as top runner transformers are becoming popular. In addition, three-phase three-wire type and three-phase four-wire type transformers are being developed as needed to improve power distribution efficiency. Furthermore, transformers are manufactured that have greatly different levels of excitation current than conventional products. When a conventional transformer failure determination device is applied to such a transformer, an erroneous determination may be made.

  Therefore, in order to solve such a problem, Patent Document 2 discloses a short-circuit determination device that can quickly and surely determine a short-circuit between windings of a transformer by a simple determination process instead of the above-described fixed threshold determination. Proposed inventions have been proposed. The transformer failure determination device (short-circuit determination device) disclosed in Patent Document 2 includes an AC power source that sequentially applies AC voltages having different frequencies to the windings of the transformer, and an excitation current of the transformer for AC voltages having different frequencies. A current measurement unit that measures current, a first-order derivative calculation unit that first-derivatizes an approximate curve of the excitation current value measured by the current measurement unit, and a differential value obtained by the first-order derivative calculation unit is positive if there is no short circuit, negative In this case, a short circuit determination unit that determines that there is a short circuit and a determination notification unit that notifies the determination result of the short circuit determination unit are provided.

  The transformer failure determination device disclosed in Patent Document 2 is excited when an AC voltage is applied by sweeping the frequency between a transformer in which windings are short-circuited and a normal transformer that is not short-circuited. It utilizes the fact that the current trajectories are different. In other words, a sound transformer has an L component due to the winding, a C component due to the insulating layer portion of the winding, and an R component due to the winding resistance, and an impedance value obtained by synthesizing these depends on the frequency. That is, the L component is dominant in the low frequency region, and the C component is dominant in the high frequency region. As a result, in the case of a normal healthy product, the current value of the excitation current tends to increase when the frequency is gradually increased. On the other hand, a transformer in a rare short state acts in a direction that eliminates the L component by a short circuit formed therein, so that the L component becomes smaller when compared with a healthy product. For this reason, C is dominant in the impedance of the entire transformer regardless of the frequency. As a result, in the case of a faulty product, the current value tends to decrease when the frequency is gradually increased.

  FIG. 2A shows the relationship between the excitation current and the frequency in each of these healthy transformers and rare-short transformers. The accident product (1) and the accident product (2) in FIG. 2 (a) are the results of measurements on the transformers shown in FIG. The accident product (1) has a rare short circuit at point (1) on the primary side, and the accident product (2) has a rare short circuit at point (2) on the secondary side.

  Therefore, the approximate curve of a plurality of excitation current values with respect to the AC voltage at the plurality of frequencies is regarded as a locus of the excitation current, and the approximate curve is first-order differentiated to determine whether the curve tends to increase or decrease. It is possible to make a determination, and it is possible to quickly and reliably determine a short circuit between windings by an easy process such as a first-order differential process.

Japanese Patent No. 117509 JP-A-7-94341

  As described above, the transformer failure determination device disclosed in Patent Document 2 can determine a short circuit between windings of the transformer by a simple process. However, when frequency-excitation current characteristics were measured for transformers simulating various patterns of accidents, the excitation current-frequency characteristics of many transformers showed healthy products as shown in FIG. As the frequency increased, the excitation current also increased and the accident product showed a tendency to decrease, but as shown in FIG. 3B, the same tendency as the healthy product (primary 1) in a specific accident pattern of a specific transformer. The case where the turn short circuit shows the tendency that the excitation current increases with the increase of the frequency in the same way as the healthy product was confirmed. When such characteristics are shown, the accident product is determined as a healthy product. Although there are only a few exception cases, there is a problem of improving the detection accuracy in order to be put to practical use.

To solve the problems described above, the transformer failure determination device according to the present invention is a transformer failure determination unit determines the presence or absence of the transformers failure, an AC voltage application means for outputting an AC voltage, wherein A fault determination unit for applying an AC voltage to the transformer by an AC voltage application means, and determining the presence or absence of a short circuit between windings of the transformer based on a phase difference between the exciting current and the AC voltage at that time; and the fault determination It is premised on a thing provided with the judgment alerting part which alert | reports the judgment result of a part .

  When power is applied without connecting a load to the healthy transformer, current flows only in the input coil. Therefore, the transformer exhibits inductivity due to the self-inductance (L component) of the coil. In practice, however, there is active power (R component) for supplying iron loss in addition to the self-inductance, so the phase difference between the input voltage and the excitation current is not 90 °. As a result of actual measurement, the phase difference is about 40 to 70 °.

  Since the transformer coil is wound in close contact with a winding coated with an insulator such as formal, it can be considered that a very small capacitive load (C component) is continuously connected in parallel. When the power supply frequency applied to the input coil is small, the influence of the C component can be ignored, but the influence increases as the frequency increases. Since the capacitive load has the effect of eliminating the inductive load, the power factor changes from inductive to capacitive when the frequency of the power supply applied to the healthy transformer increases. For this reason, the phase of the excitation current with respect to the alternating voltage applied with the increase in frequency changes from delay to advance.

  On the other hand, in a transformer short-circuited, a short-circuit winding composed of a short-circuit is present inside, so that a magnetic field is generated in a direction that erases the magnetic field of the input coil. For this reason, there is almost no L component in the transformer in the rare short state, and the phase angle difference between the applied voltage and the excitation current is almost zero. However, in the transformer in such a state, since the short-circuit winding exists in a part of the iron core, not all of the magnetic field generated by the input side coil is transmitted to the short-circuit winding (leakage magnetic flux exists). Actual measurement in a commercial frequency region such as 50 Hz shows that the current is delayed by 0 ° to 30 ° compared to the voltage. Further, this magnetic flux leakage tends to increase as the frequency increases, and the generated secondary magnetic field becomes weaker as the frequency increases. As a result, the L component of the primary coil tends to increase as the frequency increases. When the frequency is further increased, the influence of C due to the insulation of the winding becomes obvious as in the case of the healthy transformer, and therefore the degree of the delay of the excitation current with respect to the AC voltage increases. As a result of the actual measurement, an inflection point of the voltage-current phase difference was confirmed around 2 kHz in many transformers.

  In addition, depending on the type of transformer, the above-mentioned influence is small, and even when a rare short failure occurs, the degree of the phase delay of the excitation current decreases as the frequency increases in the same way as a healthy product that does not fail. Although there are things that change to advance, even in that case, there is an influence of the above-mentioned rare short compared with a healthy product, and the amount of change when the phase difference delay is reduced and advanced is reduced.

  Thus, the phase difference between the AC voltage and the excitation current differs between a healthy product that has not failed and a faulty product that has caused a winding short-circuit, so failure determination can be performed based on the phase difference. it can. And as a concrete determination algorithm, the following can be taken.

(1) Based on the above assumption, the failure determination unit determines whether or not there is a failure depending on whether the phase difference obtained when applying AC voltages having a plurality of different frequencies is increasing or decreasing. It was supposed to be.

(2) In the above premise, the failure determination unit determines the presence or absence of a failure based on the magnitude of the change in the phase difference obtained when a plurality of alternating voltages having different frequencies are applied. Can do. The plurality of different frequencies may be at least two points, but may be three or more points to be sampled.

(3) In the above premise, the failure determination unit determines the presence / absence of a failure by comparing the phase difference when an AC voltage in a commercial frequency region is applied and a set threshold value, A plurality of threshold values may be provided, and the determination result of the failure determination unit may include “unknown” that cannot be specified in addition to “failure present” and “no failure”. As a result, the probability of erroneous determination is reduced.

(4) In the above premise, the apparatus includes a degaussing unit that demagnetizes the iron core of the transformer, and an AC voltage is applied to the transformer in which the iron core is demagnetized by the demagnetizing unit, and the failure determination It is good to make a judgment in the section. The transformer core used has residual magnetic flux, and the magnitude and direction of the magnetic field are not constant. When the residual magnetic flux is large, the iron core permeability decreases and the winding inductance decreases, so that the excitation current increases. On the other hand, when the residual magnetic flux is small, the iron core permeability increases and the winding inductance increases, so the excitation current becomes small. Since the level of the residual magnetic flux in the iron core varies depending on individual transformers depending on various conditions such as the timing at which the applied voltage is turned off, the subsequent standing time, and the iron core size, the residual magnetic flux in the transformer core to be measured is unknown. Therefore, the transformer (iron core) is demagnetized by the demagnetizer, and the residual current of the iron core is set to the same condition (demagnetization). Can be determined with high accuracy.

(5) The degaussing section includes an initial processing means for applying a DC voltage to the transformer to make it a positive or negative saturation state, and a direct current for making the saturation transformer in a reverse saturation state. DC voltage application means for applying voltage, saturation detection means for detecting that the iron core of the transformer is saturated, and saturation with the saturation detection means for the transformer saturated with the initial processing means. Until the detection is detected, a DC voltage opposite to that of the initial processing means is applied, and immediately after the iron core reaches a saturated state, it is shut off, and the energy required for saturation from the start of application of the DC voltage is cut off. A saturation energy calculation means for obtaining a DC voltage in the same direction as the initial processing means is applied, and the energy applied to the transformer at the time of application is monitored, and the energy is obtained by the saturation energy calculation means. May and a control means for interrupting the application of the DC voltage having the same direction when it becomes half the value of the energy to the saturation.

  In this case, the saturation energy calculation means can obtain an integral value of the voltage value of the DC voltage. Further, the saturation detecting means may 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 applying means. Further, the DC voltage power source may be a battery. 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 and consumed unnecessarily, 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 0 and demagnetization can be performed.

  In the present invention, the iron core of the transformer can be demagnetized with a simple configuration.

It is a figure explaining the subject of this invention. It is a figure explaining the subject of this invention. It is a figure explaining the subject of this invention. It is a figure which shows suitable one Embodiment of the transformer failure determination device in which the degaussing device which concerns on this invention is integrated. 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 figure which shows the function and operation | movement principle of a demagnetizing part. It is a figure explaining the function of a demagnetizing part. It is a figure explaining the effect of this invention. It is a figure explaining the effect of this invention. It is a figure explaining the effect of this invention. It is a top view which shows the specific structure of the transformer failure determination device based on this invention.

  FIG. 4 shows a schematic configuration of the transformer failure determination device according to the present invention. As shown in FIG. 4, a probe 1 which is a measurement terminal connected to a terminal of each phase of a transformer is provided, and a demagnetizing unit 2 and a failure determination unit 3 are linked to the probe 1 via a changeover switch SW. . A demagnetizing unit 2 and a failure determining unit 3 are connected to the probe 1 in a switching manner, and are linked to terminals of each phase of a transformer that is an inspection object. Furthermore, the transformer failure determination device includes an input unit 4 as a man-machine interface and a notification unit 5. Furthermore, a power supply unit 6 for operating each unit and a measurement circuit 7 for measuring voltage and current are provided.

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

  The power supply unit 6 uses a battery in this embodiment. That is, the power supply unit 6 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 when degaussing 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 5 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 failure determination unit 3 applies an AC voltage between predetermined terminals of the transformer, determines the presence or absence of a failure according to the algorithm shown below, and outputs the determination result via the notification unit 5. In addition, a sine wave generation unit (a circuit that can be realized by a one-chip microcomputer or the like and that is amplified by an operational amplifier or the like as necessary) for applying the AC voltage is provided. Specific functions of the failure determination unit 3 will be described later.

  The demagnetizing unit 2 is for demagnetizing the transformer (iron core) prior to the measurement in the failure determination unit 3. 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. 3, the measurement result changes every time measurement is performed. . Therefore, in the present embodiment, the demagnetization unit 2 is used to demagnetize the initial state in order to avoid the influence of the residual magnetic flux.

  In general, demagnetization uses AC demagnetization in which an alternating magnetic flux (alternating voltage) is applied to the transformer once until it becomes slightly overexcited, and the magnitude of the magnetic flux (voltage) is gradually reduced. Demagnetization by this method can surely reduce the residual magnetic flux, but a voltage higher than the rated voltage is required and the device itself becomes large. Of course, such a configuration may be adopted, but in the present embodiment, the DC demagnetization is performed using the DC voltage of the power supply unit 6. In consideration of the winding resistance and the number of turns, many of the 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, demagnetization can be performed with a small voltage, so that the transformer failure determination device is also compact and portable.

  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 demagnetization unit 2 and the failure determination unit 3 to control operation in each unit. Used for determination and the like.

  Next, the function of the demagnetizing unit 2 will be described while explaining the principle of demagnetization. As is well known, the magnetization curve (BH curve) of a ferromagnetic material used for an iron core has a characteristic like a hysteresis curve as shown in FIG. 5 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 it, and as shown in FIG. 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, so that 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) in the degaussing unit 2 executing the following algorithm shown in FIG. First, the demagnetizing unit 2 puts the iron core of the transformer into 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, an example of the hysteresis curve (BH characteristic) of the iron core is as shown in FIG. 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 ensure saturation (see (1) in FIG. 8), 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 degaussing unit 2 applies a negative DC voltage to the transformer to bring the 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 degaussing unit 2 resets the first integrated voltage value V1, which is an integrated value of the voltage 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 demagnetizer 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 creates 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 magnetizing, 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. 6), it is in an unsaturated state, and in that section, the branch determination in processing step S4 remains No, so negative While the DC voltage is continuously applied, the excitation current is continuously monitored and the voltage value is integrated every sampling time.

  If the excitation current increases rapidly ("X" in FIG. 6), 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. 8). 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 degaussing 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. 8). When the counter electromotive force becomes 0, a constant negative 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 degaussing 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 the 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 demagnetizing 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 creates a new second integrated voltage. The value V2 is obtained and overwritten on the buffer memory 3 (S8). Then, the demagnetizing unit 2 determines whether or not the obtained second integrated voltage value V2 is half of the first integrated voltage value V1 corresponding to the energy required for the negative saturation state (S9). .

  If the answer is Yes in S9 (see (5) in FIG. 8), the demagnetizer 2 shuts off the power (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. The counter electromotive force is generated by this voltage interruption, and then the voltage gradually decreases and returns to 0 (see (6) in FIG. 8). 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. The specific demagnetization processing algorithm is not limited to the above, and can be realized by various types.

  Next, specific functions of the failure determination unit 3 will be described. The failure determination unit 3 of the present embodiment applies an AC voltage between the terminals of a predetermined phase of the transformer via the probe 1, and based on the phase difference between the excitation current flowing at that time and the voltage between the terminals, The presence or absence of a short circuit between the generated windings is determined. That is, a predetermined phase difference is generated between the AC voltage when the AC voltage is applied to the transformer and the excitation current according to the state of the transformer. The phase difference of the excitation current with respect to the AC voltage (excitation current phase difference) is that the phase of the excitation current lags behind the AC voltage (phase difference is +), advances (phase difference is-), or is almost equal (phase difference is 0).

<Determination based on excitation current phase difference when AC voltage is applied in the commercial frequency range>
As shown in FIG. 9, in the case of a healthy product that has not failed, the excitation current phase difference when an AC voltage of 50 Hz (first) or 100 Hz (second), which is a commercial frequency region, is applied is 40-50. The excitation current is delayed with respect to the voltage. FIG. 9A shows the characteristics of a certain lightning-proof pole transformer (10 kWA), and FIG. 9B shows the characteristics of a certain three-phase three-wire transformer (10 kVA). The applied voltage was 3 [V] in all cases. As a result of actual measurement of various transformers, when an AC voltage of 50 Hz is applied, a phase difference of about 40 to 70 ° is obtained.

  On the other hand, a transformer that is short-circuited is close to 0 with little delay in excitation current when an AC voltage is applied between the terminals that are short-circuited. In the two transformers shown in FIG. 9, the phase difference is within a range of ± 10 °, and in many cases, the phase difference is about 0 to 30 ° as a result of mounting various other transformers.

Therefore, for example, an AC voltage in the commercial frequency region such as 50 Hz is applied, and the excitation current phase difference at that time is obtained and compared with a predetermined threshold (for example, 35 ° or 40 °). If there is, it is determined as a healthy product, and if it is less than the threshold value, it can be determined as a failure (short circuit). Moreover, instead of distinguishing into two like the healthy product (OK) and the short circuit (NG), for example,
0-20 ° delay: short circuit 20-50 ° delay: unknown (gray zone)
Delay of 50 ° or more: It may be divided into three or more judgment categories such as soundness.

  In particular, as in this embodiment, demagnetization as a pre-process reduces the variation between transformers, and in many cases, in the case of a delay of less than 20 degrees, a short circuit is surely generated. Can be determined. Moreover, the occurrence of misjudgment can be prevented by providing unknown. In addition, even if it is not clear from the determination by measuring one point in the commercial frequency region, there is no problem because it can be determined accurately according to another determination rule described below.

<Determination based on the state of change in the current phase difference with increasing frequency (part 1)>
Moreover, when the frequency is gradually increased, the excitation current phase difference of the healthy product tends to decrease in any case. That is, in the initial commercial frequency region, the excitation current is delayed, but in the region where the frequency is high, the excitation current proceeds conversely.

  On the other hand, in the case of FIG. 9A, when a short circuit occurs, the excitation current phase difference tends to increase when an AC voltage is applied between the terminals causing the short circuit. That is, in the commercial frequency region, no excitation current delay is observed, but the excitation current gradually delays. However, as shown in FIG. 9B, there is a case where the excitation current phase difference changes in a decreasing tendency even when a short circuit occurs.

  Therefore, at least when the change in excitation current phase difference tends to increase when the frequency is increased, a failure (short circuit) can be determined. Such a determination can determine the excitation current phase difference at two different frequencies (for example, 100 Hz and 1 kHz), respectively, and determine whether there is a failure from the magnitude relationship. Specifically, if the phase angle of 1 kHz is larger, it is determined that there is a failure. By making simple determinations with two points in this way, the memory capacity to be used can be reduced and determination can be made in a short time, but in order to make more accurate determinations, measurements are made at three or more points. However, it may be determined based on many measurement results. Moreover, although the low frequency was set to 100 Hz, when the determination based on one point of the commercial frequency region described above is performed, it is preferable that the low frequency and the frequency used for the determination based on the one point are the same.

<Determination based on the state of change in the current phase difference with increasing frequency (part 2)>
As shown in FIG. 9B, there is a transformer that shows a tendency that the excitation current phase difference decreases as the frequency increases even when a short circuit occurs. However, the frequency characteristic of the excitation current phase difference in such a transformer tends to decrease more sharply for healthy products. Therefore, the slope of the decrease in excitation current phase difference with increasing frequency is obtained. If the slope is larger than the set threshold value, it is judged as a healthy product. It can be determined that there is a (short circuit).

  For such determination, the excitation current phase difference at two different arbitrary frequencies (for example, 100 Hz and 1 kHz) is obtained, the difference between the obtained two excitation current phase differences is obtained, and the difference exceeds the threshold value. If the difference is less than the threshold value, it can be determined that there is a failure. That is, if the two frequencies are always the same, the difference between the excitation current phase differences is proportional to the slope of the frequency characteristics. In the above example, since the two frequencies to be sampled are the same as the frequencies used in the first determination above, the excitation current phase difference measured for each determination is also shared. Processing can be simplified. In the example shown in FIG. 9B, the rate of change and the frequency of decrease of the excitation current phase difference are rapidly changed to about 500 Hz, and thereafter gradually become gentle. Therefore, for example, if the two frequencies are 1.5 kHz and 3.0 kHz, the healthy product is already saturated and the change is smaller than that of the failed product. In this case, the determination based on the excitation current phase difference at 100 Hz and 500 Hz rather than 100 Hz and 1 kHz makes the difference between a healthy product and a faulty product more prominent. It can be carried out. Therefore, in order to perform more accurate determination, it is preferable to set two frequencies at which the difference in change appears more prominently.

  Of course, if the excitation current phase difference for a larger number of frequencies is obtained, and the slope (rate of change) of the excitation current phase difference that changes as the frequency is increased based on these, more accurate judgment can be made. It is preferable in terms.

  The failure determination unit 3 performs all of the above-described three determinations, or any one or any two of them, and performs a failure determination. When a plurality of determination algorithms are executed, it is determined that there is a failure when a failure is detected by at least one determination algorithm. When a plurality of determination algorithms are executed, they may be executed in parallel or sequentially in an appropriate order. In the case of sequential execution, for example, first, an AC voltage of one frequency (for example, 100 Hz (50 Hz)) in the commercial frequency region that can be most easily determined is applied, the excitation current phase difference at that time is obtained, and a healthy product is obtained from that value. It is also possible to determine any one of / unknown (gray) / failed product and perform determination (part 1 or part 2) based on excitation current phase differences of the next plurality of frequencies only for those with gray determination. In this way, in many cases, failure determination can be performed by obtaining a single excitation current phase difference, and even in the case of gray determination, the lower frequency (100 Hz (50 Hz)) of the two frequencies. Since the excitation current phase difference is obtained, the excitation current phase difference at the other higher frequency (for example, 1 kHz) is obtained, and the excitation current phase difference at 100 Hz obtained previously is used. Since the final determination can be made, it is efficient.

  In addition, although the explanation is mixed, the excitation current phase difference is obtained, for example, by the voltage value (instantaneous value) of the AC voltage applied from the measurement circuit 7 at a constant sampling time and the excitation current value (instantaneous value) flowing at that time. Each is stored in a ring buffer memory or the like in time series. Each value is stored together with time information (time stamp). As a result, the AC voltage zero crossing point and the excitation current are calculated from the voltage value (instantaneous value) and current value (instantaneous value) history stored in the ring buffer memory for AC voltage and the ring buffer memory for excitation current. A zero-cross point can be extracted, a time difference can be obtained from time information associated with each value, and a phase difference can be obtained. Further, since the sampling time is constant, the phase difference may be obtained based on the difference between the memory area in which one zero cross point is stored and the memory area in which the other zero cross point is stored. Of course, other methods can be used.

  10 and 11 are graphs (excitation current phase difference frequency characteristics) showing the excitation current phase difference obtained when the frequency of the AC voltage to be applied is changed for a representative type of transformer. FIG. 10 shows characteristics for healthy products, and FIG. 11 shows characteristics for short-circuited products. Further, as in the present embodiment, demagnetization is performed as preprocessing.

  As shown in FIG. 10, in each of the transformers of each sample, the excitation current phase difference at 50 Hz in the commercial frequency region is within a range of 40 ° to 65 °, and the first based on the commercial frequency region. All can be determined to be healthy under the determination conditions. In all samples, it can be confirmed that as the frequency increases, the current advances with respect to the voltage and is in a relatively steep decreasing tendency.

  On the other hand, as shown in FIG. 11, all the transformers that have caused the short circuit have the excitation current phase difference at 50 Hz in the commercial frequency region within the range of 0 ° to 20 °. It can be determined that a failure has occurred in the first determination condition based on the region. It can be confirmed that the frequency characteristics of the excitation current phase difference of the transformer causing the short circuit tend to be delayed (increase tendency) in the current up to around 2 kHz in many transformers. It can also be seen that even if the frequency characteristics of the excitation current phase difference tend to advance (decrease) as the frequency increases, the change is relatively gentle.

  FIG. 12 shows an example of the hardware configuration of this embodiment. Members corresponding to those of the schematic configuration shown in FIG. Further, the demagnetizing unit 2 and the failure determination unit 3 are realized by the same member in the hardware configuration.

  As shown in the figure, the power supply unit 6 is driven by a direct current such as a dry battery having a voltage of 4.8 to 6 [V] and an output of 4 to 5 [W]. Considering versatility and running cost, the battery 6a such as an AA alkaline manganese battery or a nickel metal hydride battery can be used. The outputs of these batteries 6a are given to the stabilization circuit 6b, where a DC voltage of 3 [V] is generated.

  The output of the stabilization circuit 6 b is given to the probe via the cutoff switch 27, the positive / negative switch 24, and the direct current / alternative selection switch 28. In addition, a measurement circuit 7 that measures applied voltage, excitation current, and the like is also provided, and the output of the measurement circuit 7 is given to the one-chip microcomputer 22. Switching control of each switch is performed based on a control signal from the one-chip microcomputer 22. Since the cut-off switch 27 has a function to open and close, the switch element such as an FET can be used at high speed.

  When the cutoff switch 27 is closed, the output of the stabilization circuit 6 b is given to the positive / negative switch 24. The one-chip microcomputer 22 controls the shut-off switch 27 to be closed when a DC voltage is applied to the iron core for demagnetization, and to open the shut-off switch 27 when the iron core is saturated and shuts off the power supply. .

  The positive / negative selector switch 24 switches the direction (positive / negative) of the voltage applied to the transformer, and is a switch circuit that inverts the positive / negative side by switching the switch. By this switching, a positive DC voltage is applied to the transformer to be in a positive saturation state, or a negative DC voltage in the opposite direction is applied to be in a negative saturation state.

  The DC / AC switch 28 switches the type of power supply when applied to the probe. In the state shown in the figure, a DC voltage is applied for demagnetization, and in the state connected to the operational amplifier 25 side, An AC voltage is applied to detect a short circuit between windings.

  The one-chip microcomputer (one-chip CPU) 22 has a function of generating and outputting a sine wave (sine wave generating unit 22a) and controls the entire apparatus. The demagnetizing unit 2 shown in FIG. The function of the failure determination unit 3 is provided. The output of the sine wave generator 22a is amplified by the operational amplifier 25 (power supply voltage is ± 12 [V]) and then applied to the transformer via the measurement circuit 26.

  The one-chip microcomputer 22 receives an input signal from a switch / operation button as an input unit provided on the upper surface of a case (not shown), executes a predetermined process, and uses the execution result as an output signal as an indicator serving as a notification unit. , Buzzer, etc., and a predetermined notification (determination result, etc.)

DESCRIPTION OF SYMBOLS 1 Probe 2 Demagnetizing part 3 Failure determination part 4 Input part 5 Notification part 6 Power supply part

Claims (5)

A transformer failure determination device for determining the presence or absence of a transformer failure,
AC voltage application means for outputting an AC voltage;
Applying an alternating voltage to the transformer with the alternating voltage application means, a failure determination unit for determining the presence or absence of a short circuit between windings of the transformer based on the phase difference between the exciting current and the alternating voltage at that time,
A determination notification unit that notifies the determination result of the failure determination unit;
With
The failure determination unit is configured to determine whether or not there is a failure depending on whether the phase difference obtained when applying AC voltages having a plurality of different frequencies is increasing or decreasing. Transformer failure determiner. A transformer failure determination device for determining the presence or absence of a transformer failure,
AC voltage application means for outputting an AC voltage;
Applying an alternating voltage to the transformer with the alternating voltage application means, a failure determination unit for determining the presence or absence of a short circuit between windings of the transformer based on the phase difference between the exciting current and the alternating voltage at that time,
A determination notification unit that notifies the determination result of the failure determination unit;
With
The failure determination unit is configured to determine the presence or absence of a failure based on the magnitude of change in the phase difference obtained when a plurality of alternating voltages having different frequencies are applied. vessel. A transformer failure determination device for determining the presence or absence of a transformer failure,
AC voltage application means for outputting an AC voltage;
Applying an alternating voltage to the transformer with the alternating voltage application means, a failure determination unit for determining the presence or absence of a short circuit between windings of the transformer based on the phase difference between the exciting current and the alternating voltage at that time,
A determination notification unit that notifies the determination result of the failure determination unit;
With
The failure determination unit is configured to determine the presence or absence of a failure by comparing the phase difference and a set threshold when an alternating voltage in a commercial frequency region is applied,
A plurality of the threshold values are provided, and the determination result of the failure determination unit includes “unknown” in addition to “failure present” and “no failure”. A transformer failure determination device for determining the presence or absence of a transformer failure,
AC voltage application means for outputting an AC voltage;
Applying an alternating voltage to the transformer with the alternating voltage application means, a failure determination unit for determining the presence or absence of a short circuit between windings of the transformer based on the phase difference between the exciting current and the alternating voltage at that time,
A determination notification unit that notifies the determination result of the failure determination unit;
With
Comprising a degaussing part for demagnetizing the iron core of the transformer,
A transformer failure determiner, wherein an AC voltage is applied by the AC voltage applying means to the transformer whose core has been demagnetized by the demagnetizer, and the failure determiner determines. The demagnetizing part is
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.
A DC voltage in the same direction as the initial processing means is applied, and the energy applied to the transformer at the time of application is monitored, and the energy becomes half of the energy to be saturated obtained by the saturation energy calculating means. Control means for interrupting the application of the direct-current voltage in the same direction,
The transformer failure determination device according to claim 4, comprising:

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