JP7072984B2 - Switch life diagnostic device - Google Patents

Description

An embodiment of the present invention relates to a life diagnosis device that provides data for life diagnosis of a switch provided in a power line that supplies an electric current to an AC arc furnace.

In switches such as disconnectors and circuit breakers, abnormalities occur on the contact surface of the conductive part due to the surrounding environment, usage conditions, deterioration over time, etc., and contact resistance increases. If energization is continued with the contact resistance increased, the contact surface may be overheated, resulting in burning at worst. Therefore, conventionally, the contact resistance on the conductor contact surface is measured and the temperature is monitored in the maintenance and inspection of switches such as disconnectors and circuit breakers.

Japanese Unexamined Patent Publication No. 8-83544

Conventionally, there is a four-terminal measurement method as a method for measuring contact resistance on the conductor contact surface of a switch, but the main circuit to which the switch is connected must be stopped for measurement. On the other hand, as a technique for monitoring the deterioration status of the switch while keeping the main circuit alive, there are a method using a temperature indicator tape and a temperature measurement using an infrared radiation temperature measuring device. However, the former can be judged only when an abnormality occurs, and the latter has the complexity that the judgment value must always be corrected in consideration of the temperature change due to the surrounding environment.

In plant equipment such as an AC arc furnace, it is desirable to avoid frequent outages or prolonged outages. Therefore, there is a strong demand for predicting the life of the switch used in such equipment and performing repair or replacement work during the scheduled maintenance period or operation suspension period.

Switches used for power lines that handle high-voltage and large currents, such as AC arc furnaces, have extremely low contact resistance, so some ingenuity is required during measurement.

The embodiment of the present invention has been made to solve the above-mentioned problems, and the estimated value of contact resistance calculated by measuring the voltage and current across the switch using a simple measurement system is obtained. Provided is a switch life diagnosis device for diagnosing the life of a switch by monitoring.

The switch life diagnostic device according to the embodiment diagnoses the life of the switch provided in the supply line that supplies current to the electrodes of the AC arc furnace. This life diagnostic device acquires a set of voltage difference data across the switch and current flowing through the switch a plurality of times at different times, and each time the set of data is acquired, the said The current data is compared with a predetermined current threshold value, and when the current data is equal to or higher than the current threshold value, the voltage difference data and the current data obtained at the same time are used. A calculation unit is provided that calculates and stores the resistance value of the switch and generates an alarm signal when the resistance value is equal to or higher than a predetermined first resistance threshold value. The calculation unit calculates the resistance component calculated based on the phase difference between the voltage difference and the current as the resistance value.

In the present embodiment, when a current exceeding the threshold value flows, the voltage difference across the switch and the current data are acquired, the resistance value is calculated, and whether or not the resistance value is equal to or higher than the predetermined threshold value. Since the degree of deterioration is determined by, the estimated value of contact resistance can be easily obtained with a small error.

It is a block diagram which illustrates the life diagnosis apparatus of the switch which concerns on 1st Embodiment. It is an example of the flowchart for demonstrating the operation of the life diagnosis apparatus of the switch of 1st Embodiment. It is an example of the flowchart for demonstrating the operation of the life diagnosis apparatus of the switch of 1st Embodiment. It is a schematic graph which shows the time-dependent change of the contact resistance for diagnosing the life of a switch. It is a block diagram which illustrates the life diagnosis apparatus of the switch which concerns on 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
It should be noted that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio of the sizes between the parts, and the like are not necessarily the same as the actual ones. Further, even when the same part is represented, the dimensions and ratios may be different from each other depending on the drawing.
In addition, in the present specification and each figure, the same elements as those described above with respect to the above-mentioned figures are designated by the same reference numerals, and detailed description thereof will be omitted as appropriate.

(First Embodiment)
FIG. 1 is a block diagram illustrating the life diagnosis device of the switch according to the first embodiment.
As shown in FIG. 1, in the life diagnosis device 10 of the present embodiment, the switch 1 is provided in series with the power line 20 so as to open and close the current flowing through the power line 20. The power line 20 supplies a current to the electrodes of the AC arc furnace. In the AC arc furnace, electrodes are provided in each phase of the three-phase alternating current. There are three conductor contact portions 1a of the switch 1 according to the three-phase alternating current, and one is provided for each phase. The three conductor contact portions 1a open and close at the same time according to the opening and closing of the switch 1. The life diagnosis device 10 collects data regarding the conductor contact portion 1a of each phase, and provides data for life diagnosis and the like for each phase of the switch. In the following, unless otherwise specified, the life diagnosis of the switch in one phase during three-phase alternating current will be described.

The switch 1 includes terminals 1b and 1c. Inside the switch 1, both ends of the conductor contact portion 1a are electrically connected to the terminals 1b and 1c. The switch 1 is connected to the power line 20 via the terminals 1b and 1c. The conductor contact portion 1a is electrically or manually opened and closed between the terminals 1b and 1c by an opening / closing mechanism (not shown). The terminals 1b and 1c are electrically connected to the inner conductor contact portion 1a so as to have the shortest distance.

High-voltage side (primary side) wiring of the voltage measuring instruments 2a and 2b is connected to both ends of the switch 1. The primary side wirings of the voltage measuring instruments 2a and 2b are connected from both ends of the conductor contact portion 1a so as to be the shortest. Preferably, the primary side wiring of the voltage measuring instruments 2a and 2b is connected to the terminals 1b and 1c of the switch 1. By connecting in the shortest time in this way, the inductance due to the wiring between the switch 1 and the power line 20 can be reduced, and it is possible to suppress the occurrence of a phase shift when acquiring the voltage difference across the switch 1. ..

The low voltage side (secondary side) wiring of the voltage measuring instruments 2a and 2b is connected to the input of the differential amplifier 3. In the voltage measuring instruments 2a and 2b, the step-down rate is appropriately set according to the voltage across the switch 1 and the input voltage range of the differential amplifier 3. Depending on the required step-down rate, voltage measuring instruments may be connected in series and used.

Here, when the high voltage side (primary side) of the voltage measuring instruments 2a and 2b is measuring the first phase voltage, for example, the low voltage side (secondary side) wiring of the voltage measuring instrument 2a is on the first phase side. The voltage is input to the first terminal of the differential amplifier 3, and the low voltage side (secondary side) wiring of the voltage measuring instrument 2b is input to the second terminal of the differential amplifier on the first phase side. Further, the neutral point side wiring of the voltage measuring instrument 2a and the voltage measuring instrument 2b are both connected to the common potential (for example, the ground potential) of the differential amplifier 3.

The differential amplifier 3 amplifies the voltage difference between both ends of the switch 1 acquired by the voltage measuring instruments 2a and 2b with a preset amplification factor G and outputs the voltage. The output of the differential amplifier 3 is connected to the life diagnostic device 10 via the voltage converter 4. The voltage converter 4 is, for example, an analog-digital converter, and converts the voltage difference data of the analog values acquired by the voltage measuring instruments 2a and 2b into digital values and supplies the data to the life diagnosis device 10.

The power line 20 is provided with a current measuring device 5. The current measuring device 5 is connected to the life diagnostic device 10 via the current converter 6. The current measuring device 5 measures the current flowing through the power line 20, that is, the current flowing through the switch 1, and supplies the current data to the life diagnosis device 10. The current converter 6 is, for example, an analog-digital converter, and converts the current data of the analog value acquired by the current measuring device 5 into a digital value and supplies the current data to the life diagnosis device 10.

The life diagnosis device 10 calculates the contact resistance of the switch 1 based on the voltage difference and current data at both ends of the switch 1 supplied via the voltage converter 4 and the current converter 6. As will be described in detail later, the calculated contact resistance data is compared with a predetermined threshold value as an estimated value of the contact resistance of the switch 1. When the estimated value of contact resistance is equal to or greater than a predetermined threshold value, the life diagnostic device 10 generates an alarm signal for outputting an alarm indicating that the life of the switch 1 is near.

The calculation of contact resistance is calculated based on the data acquired in a predetermined period. Therefore, even if the estimated value of contact resistance is smaller than the predetermined threshold value, if the degree of change in the estimated value of contact resistance becomes greater than or equal to the predetermined threshold value over time, an alarm is given. Generate a signal.

The life diagnosis device 10 obtains an estimated value of the contact resistance of the switch 1 that opens and closes the current flowing through the power line that supplies the current to the electrodes of the AC arc furnace. Since the current flowing through the switch 1 is very large, the contact resistance of the switch 1 is also designed to be very small. Therefore, in the life diagnosis device 10 of the present embodiment, the contact resistance is estimated when a large current is flowing through the switch 1, such as when an arc discharge is generated. Therefore, the contact resistance can be estimated more accurately than when the estimated value at the time of a small current is obtained.

The life diagnosis device 10 includes a calculation unit 12. The life diagnosis device 10 inputs the above-mentioned data and calculates an estimated value of contact resistance by the calculation unit 12. The life diagnosis device 10 may include a storage unit 14. The storage unit 14 stores the supplied data and the calculated result. The measurement of the data is executed, for example, at a fixed cycle, and the acquired data is associated with the acquisition time and stored in the storage unit 14.

For example, the acquired data and contact resistance estimates are grouped according to the acquisition time. The group is, for example, data regarding the acquisition time within the same day. The estimated value of the contact resistance acquired within the same day is obtained by obtaining the average value of the day and compared with the latest acquired estimated value data as the past data of the contact resistance. Instead of taking a simple mean, the group's data may be statistically processed, the variance may be determined, the data exceeding a predetermined variance may be removed, and then the mean of the remaining data may be taken. By appropriately performing arbitrary data operations in this way, it is possible to reduce the data acquisition error.

The life diagnosis device 10 may include, for example, a storage unit such as a CPU (Central Processing Unit) or a device that sequentially reads steps of a program stored in the storage device and executes processing in response to a command, instruction, or the like of each step. good. The calculation unit 12 is a CPU, and executes and processes a part or all of each step of the flowchart described below.

The life diagnostic device 10 may include, for example, a CPU of a programmable controller (PLC). In this case, the differential amplifier 3, the voltage converter 4, and the current converter 6 may be realized as an IO module of PLC. The PLC may be further connected to a computer terminal via a communication network, and the computer terminal may execute processing based on the data collected by the PLC.

The operation of the life diagnosis device 10 of the present embodiment will be described with reference to a flowchart.
2 and 3 are examples of a flowchart for explaining the operation of the life diagnosis device of the present embodiment.
As shown in FIG. 2, in step S1, the calculation unit 12 inputs data and stores the input data in the storage unit 14 together with the acquisition time. The data in this case are the digital data ΔV of the voltage difference between both ends of the switch 1 output from the voltage converter 4 and the digital data I of the current flowing through the switch 1 output from the current converter 6. be. At this time, the threshold value It of the current data I, the threshold value S of the estimated value Za of the contact resistance, and the threshold value αt of the change α of the contact resistance may be input and set at the same time. These data are stored in the storage unit 14 in advance.

In step S2, the calculation unit 12 determines whether or not the current data I is equal to or higher than the preset threshold value It. The threshold value It is set to a value sufficiently large enough to detect the voltage difference between both ends of the switch 1 with sufficient accuracy. The threshold value It is set based on, for example, the value of the current that flows when an arc discharge occurs. When the current data I is equal to or greater than the threshold value It, the arithmetic unit 12 shifts the process to the next step S3. When the current data I is smaller than the threshold value It, the arithmetic unit 12 returns to step S1 and waits until the input of the next data.

In step S3, the calculation unit 12 calculates the estimated value Za of the contact resistance. The contact resistance estimate Za is calculated based on the differential voltage data and the current data. Assuming that the primary voltage of the voltage measuring instrument 2a is Vx and the primary voltage of the voltage measuring instrument 2b is Vy, the estimated value Za of the contact resistance can be expressed by the following equation (1).

Za = (Vx-Vy) / I (1)

In this example, equation (1) is obtained by the configuration of FIG. That is, the voltage difference actually acquired is the voltage Vx1 and Vy1 appearing on the secondary side of the voltage measuring instruments 2a and 2b. The step-down ratio k of the voltage measuring instruments 2a and 2b is the same. Therefore, Vx = k · Vx1 and Vy = k · Vy1.

The value of the voltage difference actually input to the voltage converter 4 is ΔV = G · (Vx1-Vy1). In the life diagnostic apparatus 10, based on the value of the voltage difference thus obtained, the estimated value Za of the contact resistance of the switch 1 is obtained as shown in the following equation (2).

Za = (k / I) · (ΔV / G) (2)

In step S4, the calculation unit 12 determines whether or not the estimated value Za of the contact resistance is equal to or greater than the preset contact resistance threshold value S. When the estimated value Za of the contact resistance is equal to or higher than the threshold value S, the calculation unit 12 shifts the process to the next step. If the estimated value Za of the contact resistance is smaller than the threshold value S, the next step S5 is skipped and the process is shifted to step S6.

In step S5, the arithmetic unit 12 generates an alarm signal. The alarm signal is supplied to a display, a speaker, or the like (not shown) to indicate that the switch 1 is nearing the end of its life. After generating the alarm signal, the calculation unit 12 stores the estimated value Za of the contact resistance in the storage unit 14 in step S6.

In step S6, the calculation unit 12 stores the calculated estimated value Za of the contact resistance in the storage unit 14.

In step S7, the calculation unit 12 determines whether or not the set period has elapsed. The set period represents a group of data for reducing the error of the estimated value. For example, the set period is set to one day. The calculation unit 12 groups the data for each acquisition date according to the time data associated with the acquired data. When the date is changed, the calculation unit 12 assumes that the set period has elapsed and shifts the process to the next step S8. In the case of the same date, the calculation unit 12 repeats the process in step S1 until the date changes.

In step S8, the calculation unit 12 calculates the average value of the estimated value Za within the set period.

In step S9, the calculation unit 12 calculates the change (difference) α of the estimated value Za of the contact resistance stored in the storage unit 14 from the past data.

In step S10, the calculation unit 12 calculates, for example, the difference α between the average value of the current day and the average value of the previous day, and compares the calculation result with the preset threshold value αt.

When the difference α of the estimated daily contact resistance value Za of the estimated contact resistance value is equal to or greater than the threshold value αt, the calculation unit 12 shifts the process to the next step S11. In step S11, the arithmetic unit 12 generates an alarm signal. After that, the calculation unit 12 returns the process to step S1 and repeats the above operation.

If the difference α is smaller than the threshold value αt in step S10, the arithmetic unit 12 shifts the process to the subprogram.

The subprogram estimates the contact resistance of the switch for each phase of the AC arc furnace, and if a deterioration tendency of the contact resistance of the switch of any phase is recognized, not limited to a specific phase, an alarm signal is sent. To generate. In this case, the arithmetic unit 12 acquires the above-mentioned data regarding the switch 1 corresponding to all the phases, the estimated value Zar of the contact resistance of the first phase, the estimated value Zar of the contact resistance of the second phase, and the estimated value Zar of the contact resistance of the second phase. The estimated value Zat of the contact resistance of the third phase is calculated.

As shown in FIG. 3, in step SB1, the arithmetic unit 12 inputs estimated values of contact resistance for three phases, Zar, Zas, and Zat.

In step SB2, the calculation unit 12 calculates the average value Aave2 of the estimated values Zar, Zas, and Zat of the contact resistance for the three phases.

In step SB3, the calculation unit 12 calculates ΔZar, ΔZas, ΔZat which is the difference between the estimated value Zar, Zas, Zat of the contact resistance of each phase and the average value Zave2.

In step SB4, the calculation unit 12 presets the difference between the estimated value of the contact resistance of each phase and the average value thereof, that is, the difference ΔZar, ΔZas, ΔZat with the average value of the contact resistance of each phase. It is determined whether or not the threshold value is ΔAt or more. When at least one of the differences ΔZar, ΔZas, and ΔZat from the average value of the contact resistance of each phase is equal to or greater than the threshold value ΔAt, the arithmetic unit 12 shifts the process to the next step SB5, and in SB5. , Generate an alarm signal.

If any of the differences ΔZar, ΔZas, and ΔZat from the average value of the contact resistance of each phase in step SB4 is smaller than the threshold value ΔAt, the arithmetic unit 12 returns the process to step S1.

The above-mentioned determination criteria can be appropriately and arbitrarily set according to the operating conditions of the AC arc furnace and the like. For example, it is not limited to at least one of the three phases, and it may be determined whether or not the threshold value has been exceeded in a plurality of phases.

The effect of the life diagnosis device 10 of the embodiment will be described.
In the present embodiment, the voltage across the switch 1 is detected and amplified by the differential amplifier 3, so that a small voltage difference can be acquired more accurately.

Further, as described in the section of operation description, in the present embodiment, when a current larger than a predetermined threshold current flows, the current value and the difference voltage are acquired. In an AC arc furnace, a large current intermittently flows through the power line 20, and the voltage drop generated at both ends of the switch 1 tends to be large. Therefore, it is possible to estimate the contact resistance of the switch 1, which normally has a very small value, with a smaller error.

Further, in the embodiment, in order to absorb the error due to the acquisition of the minute voltage, the estimated value of the contact resistance acquired at different times is calculated and stored in a plurality of units, and the average value is calculated and stored. Get the change. In this example, the estimated values acquired a plurality of times in a day are stored, and the average value in a daily unit is calculated and the calculation result is stored. Generates an alarm signal based on the degree of change in contact resistance increments by calculating the difference between the currently acquired estimate and the stored past data mean and comparing it to the threshold. be able to.

By adding the IO module of PLC by devising as described above, the measurement system can be easily configured, and the life of the switch 1 can be grasped without stopping the operation of the AC arc furnace. ..

FIG. 4 is a schematic graph showing the change over time in contact resistance for diagnosing the life of a switch.
As shown by the solid line in FIG. 4, the contact resistance gradually increases with the passage of time, and by reaching the set threshold value S, the life can be estimated and the deterioration time requiring replacement or the like can be diagnosed. .. An example is shown in which when the contact resistance reaches S0, replacement or the like is required depending on the life. In the case of a switch having deterioration characteristics of a solid line, the life of the switch is estimated by setting the contact resistance corresponding to the appropriate time T before the time T0 when the contact resistance reaches S0 as the threshold value S. At the same time, the switch can be replaced or maintained before a problem occurs.

As shown by the broken line in FIG. 4, the tendency of the contact resistance of the switch to deteriorate rapidly increases at a certain time, and may show a tendency to lead to a failure. In such a case, after reaching the set threshold value S, the life is reached at a stage T1 earlier than T0. In the present embodiment, the past estimated data is compared with the current estimated data, and if the increment is equal to or greater than a predetermined threshold value, the life diagnostic apparatus 10 can generate an alarm signal. , The life can be predicted more reliably. When predicting the life, the time value is not a simple time, but the integrated time only while the switch is closed or the integrated time only when there is an energizing current of a predetermined value or more is used for life estimation. It may be an effective time to be used.

(Second embodiment)
FIG. 5 is a block diagram illustrating the life diagnosis device of the switch according to the second embodiment.
This embodiment is a modification of the first embodiment, in which the circuits from the low voltage side (secondary side) wiring of the voltage measuring instruments 2a and 2b to the differential amplifier 3 are different, and the others are the first embodiment. Is similar to.

As shown in FIG. 5, the low voltage side (secondary side) wiring of the voltage measuring instrument 2a and the low voltage side (secondary side) wiring of the voltage measuring instrument 2a are connected in series with opposite polarities. That is, when the high voltage side (primary side) wirings of the voltage measuring instruments 2a and 2b each measure the phase voltage of the first phase, the inside of the low voltage side (secondary side) wiring of the voltage measuring instrument 2a. The sex point side is connected to the wiring on the neutral point side of the low voltage side (secondary side) wiring of the voltage measuring instrument 2b. Further, the low voltage side (secondary side) wiring of the voltage measuring instrument 2a is connected to the first terminal of the resistor 7 on the first phase side. The second terminal of the resistor 7 is connected to the first input terminal of the differential amplifier 3A.

The first phase side of the low voltage side (secondary side) of the voltage measuring instrument 2b is connected to the common potential (for example, ground potential) of the differential amplifier 3A together with the second input terminal of the differential amplifier 3A. Further, an overvoltage protection element 8 is connected between the first input terminal and the second input terminal of the differential amplifier 3A. The differential amplifier 3A may be configured by, for example, an operational amplifier. The overvoltage protection element 8 may be composed of, for example, a varistor or a bidirectional Zener diode. Here, it is assumed that the input impedance of the differential amplifier 3A is sufficiently larger than the impedance of the resistor 7.

In such a configuration, the low voltage side wiring of the voltage measuring instrument 2a and the low voltage side wiring of the voltage measuring instrument 2b are connected in opposite polarities. A voltage corresponding to the voltage difference between both ends of the switch 1 (corresponding to the step-down ratio of the voltage measuring instruments 2a and 2b) is directly output between them. Therefore, a voltage corresponding to the voltage difference between both ends of the switch 1 is also applied to the first input terminal of the differential amplifier 3A. Since the second terminal of the differential amplifier 3A is connected to a common potential, the differential amplifier 3A has a voltage difference between both ends of the switch 1 at a preset amplification factor G as in the second embodiment. It can be voltage amplified and output. In the first embodiment, the output amplitudes of the voltage measuring instruments 2a and 2b are applied to the input terminals of the differential amplifier as they are, whereas in the second embodiment, the voltage measuring instruments 2a are applied. , 2b voltage difference will be input, and it will be possible to configure with an amplifier with a small input dynamic range.

The resistor 7 and the overvoltage protection element 8 form a protection circuit. When the switch 1 is in the open circuit state and there is no protection circuit, the voltage on the low voltage side of the voltage measuring instrument 2a is applied as it is between the first input terminal and the second input terminal of the differential amplifier 3A. , The input voltage can be limited by the protection circuit.

Further, in the description of the equations (1) and (2) for obtaining the contact resistance in the first embodiment described above, the inductance between the terminals 1b and 1c of the switch 1 is calculated as negligible. The phase difference of the voltage difference Vx-Vy between the current data I measured by the current measuring device 5 and the terminal of the switch 1 is obtained, and these values are used to calculate the inductance component and the contact resistance component separately. The contact resistance component may be discriminated.

Further, since the number of times of opening and closing is an important factor for the deterioration of the contacts of the switch 1 in addition to the energization time, steps S7 and S8 may include the number of times of opening and closing as a condition other than the time element of the switch 1.

According to the embodiment described above, the switch is operated by measuring the voltage and current at the contact portion of the switch using a simpler measurement system, calculating the contact resistance, and monitoring the tendency of the calculated data. It is possible to realize a life diagnosis device for a switch that can diagnose the life of a switch.

Although some embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention and its equivalents described in the claims. In addition, each of the above-described embodiments can be implemented in combination with each other.

1 switch, 2a, 2b voltage measuring instrument, 3,3A differential amplifier, 4 voltage measuring instrument, 5 current measuring instrument, 6 current converter, 7 resistor, 8 overvoltage protection element, 10 life diagnostic device, 12 arithmetic unit , 14 Memory

Claims (4)

A life diagnostic device that diagnoses the life of a switch installed in a supply line that supplies current to the electrodes of an AC arc furnace.
A set of voltage difference data across the switch and current flowing through the switch is acquired multiple times at different times.
Each time a set of these data is acquired, the current data is compared with a predetermined current threshold value.
When the current data is equal to or higher than the current threshold value, the resistance value of the switch is calculated and stored based on the voltage difference data and the current data acquired at the same time.
A calculation unit that generates an alarm signal when the resistance value is equal to or higher than a predetermined first resistance threshold value is provided .
The calculation unit is a switch life diagnosis device that calculates a resistance component calculated based on the phase difference between the voltage difference and the current as the resistance value . In the calculation unit, when the resistance value is smaller than the first resistance threshold value, and the magnitude of the resistance change calculated from the stored time-series data of the resistance value is determined by the predetermined resistance change. The switch life diagnostic device according to claim 1, which generates an alarm signal when the value is equal to or higher than the value. The life diagnosis device for a switch according to claim 1 or 2 , wherein the calculation unit uses data of the voltage difference measured by a voltage measuring device connected to a connection terminal of the switch. The first switch provided in the first supply line that supplies current to the first electrode connected to the first phase of the three-phase power supply connected to the AC arc furnace, the second of the three-phase power supplies. A current is supplied to the second switch provided in the second supply line that supplies current to the second electrode connected to the phase, and the third electrode connected to the third phase of the three-phase power supply. It is a life diagnosis device for diagnosing the life of the third switch provided in the third supply line.
The first set of the data of the first voltage difference which is the voltage difference between both ends of the first switch and the data of the first current flowing through the first switch are acquired a plurality of times at different times, and the first is said. Each time a set of 1 is acquired, the data of the first current is compared with a predetermined current threshold value, and when the data of the first current is equal to or higher than the current threshold value, the first current acquired at the same time. The first resistance value of the first switch is calculated and stored based on the data of one voltage difference and the data of the first current.
The second set of the data of the second voltage difference, which is the voltage difference between both ends of the second switch, and the data of the second current flowing through the second switch are acquired a plurality of times at different times. Each time two sets are acquired, the data of the second current and the current threshold value are compared, and when the data of the second current is equal to or higher than the current threshold value, the second current is acquired at the same time. The second resistance value of the second switch is calculated and stored based on the voltage difference data and the second current data.
The third set of the data of the third voltage difference which is the voltage difference between both ends of the third switch and the data of the third current flowing through the third switch are acquired a plurality of times at different times, and the first is said. Each time a set of 3 is acquired, the data of the third current and the current threshold value are compared, and when the data of the third current is equal to or higher than the current threshold value, the third current is acquired at the same time. A calculation unit that calculates and stores the third resistance value of the third switch based on the voltage difference data and the third current data is provided.
The arithmetic unit
The resistance component calculated based on the phase difference between the first voltage difference and the first current is calculated as the first resistance value.
The resistance component calculated based on the phase difference between the second voltage difference and the second current is calculated as the second resistance value.
The resistance component calculated based on the phase difference between the third voltage difference and the third current is calculated as the third resistance value.
The arithmetic unit
When the first resistance value is smaller than the predetermined first resistance threshold value, and the magnitude of the resistance change calculated from the stored time-series data of the first resistance value is the predetermined resistance change threshold. If it is less than the value,
The average value of the first resistance value, the second resistance value and the third resistance value was calculated, and the average value was calculated.
The first difference between the first resistance value and the average value, the second difference between the second resistance value and the average value, and the third difference between the third resistance value and the average value are calculated, respectively. ,
The first difference is equal to or greater than a predetermined second resistance threshold, the second difference is equal to or greater than the second resistance threshold, or the third difference is greater than or equal to the second resistance threshold. In some cases, a switch life diagnostic device that generates a second alarm signal.

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