JP7532276B2 - Partial Discharge Detection Method - Google Patents

Description

An embodiment of the present invention relates to a partial discharge detection method.

Inverters that convert DC voltage into three-phase AC voltage are available. In such inverters, discharges (partial discharges) can occur between the three bus bars, along the surface of the insulator, or in the switching elements. Discharges occur at the rising edge of a pulse, for example. As a result, the period in which the discharge occurs matches the period of noise from switching, etc. Furthermore, the frequencies of the noise and partial discharges overlap. As a result, there is a problem in that it is difficult to detect discharges even when performing a fast Fourier transform or wavelet transform on the measurement results of the potential of the inverter panel, etc.

JP 2019-211447 A

To solve the above problem, we provide a partial discharge detection method that can effectively detect discharges that occur in the device.

According to an embodiment, the partial discharge detection method measures a parameter associated with a discharge occurring in an apparatus, sets a number of thresholds, counts pulses of the measured parameter, and outputs a warning indicating that a discharge is occurring in the apparatus based on the number of counted pulses, wherein counting the pulses means counting pulses whose wave height exceeds each of the thresholds .

FIG. 1 is a diagram illustrating an example of the configuration of a detection system according to an embodiment. FIG. 2 is a block diagram illustrating an example of the configuration of the information processing device according to the embodiment. FIG. 3 is a diagram showing the measurement results of the information processing device according to the embodiment. FIG. 4 is a graph showing the number of pulses counted by the information processing device according to the embodiment. FIG. 5 is a diagram showing the measurement results of the information processing device according to the embodiment. FIG. 6 is a graph showing the number of pulses counted by the information processing device according to the embodiment. FIG. 7 is a flowchart illustrating an example of the operation of the information processing device according to the embodiment.

The following describes the embodiment with reference to the drawings.

The detection system according to the embodiment mainly detects partial discharges that occur in a converter board that has an inverter or converter built in. The inverter may generate a surge voltage at the rising edge of a pulse due to impedance mismatch, etc. (inverter surge). When the surge voltage is superimposed on the pulse voltage, partial discharges may occur between the busbars. The detection system detects partial discharges that occur between the busbars of the inverter, etc.

Figure 1 shows an example of the configuration of a detection system 100 according to an embodiment. As shown in Figure 1, the detection system 100 includes an inverter 10, an information processing device 20, an A/D converter 30, and a sensor 40. The sensor 40 is connected to the A/D converter 30. The A/D converter 30 is connected to the information processing device 20.

The inverter 10 (power converter) converts DC voltage into AC voltage. The inverter 10 outputs three-phase (u-phase, v-phase, w-phase) AC voltage. The three-phase AC voltages are AC voltages that are 120° out of phase with each other. For example, the inverter 10 supplies three-phase AC voltage to a motor that drives an elevator or the like.

The inverter 10 includes bus bars 2 (bus bars 2a and 2b) that input a DC voltage. The positive pole of the DC voltage is connected to bus bar 2a. The negative pole of the DC voltage is connected to bus bar 2b.

The busbar 2 is connected to the inverter element 4. The inverter element 4 has three legs, each of which has a plurality of semiconductor switches that form an upper arm and a lower arm. Each leg switches the connection between the busbar 2 and the busbar 1 using a semiconductor switch. Each leg outputs AC voltages that are 120° out of phase with each other by controlling the on/off of the semiconductor switch. Each leg outputs AC voltages of the u-phase, v-phase, and w-phase, respectively.

Busbar 1 is connected to inverter element 4. Busbar 1 outputs an AC voltage. Busbar 1 is composed of busbars 1a, 1b, and 1c. Busbars 1a, 1b, and 1c output AC voltages of u-phase, v-phase, and w-phase, respectively. Busbars 1a, 1b, and 1c are connected to each leg of inverter element 4.

A surface insulating layer 4a is formed on the upper surface of busbar 1a and the lower surface of busbar 1c. In addition, an interlayer insulating layer 4b is formed between busbar 1a and busbar 1b, and between busbar 1b and busbar 1c.

A snubber unit 5 is attached to the inverter element 4. The snubber unit 5 is fixed to the inverter element 4 together with the busbar 1 and the busbar 2 by fixing screws 6.

The snubber unit 5 includes multiple snubber elements 5a. The snubber unit 5 suppresses surge voltages that occur when the legs of the inverter element 4 are switched.

The sensor 40 measures a parameter that is associated with the occurrence of a partial discharge. For example, the parameter increases (or decreases) when a partial discharge occurs.

Here, the sensor 40 is composed of a TEV (Transient Earth Voltage) sensor (transient earth potential sensor) that measures the potential of the panel surface (or the housing of the inverter 10) on which the inverter elements 4 and the like are formed as a parameter.

The sensor 40 may also be a sensor that measures, as a parameter, the current flowing through a ground wire (e.g., the ground wire of a CT) that is connected to a panel (or the housing of the inverter 10) on which the inverter elements 4 and the like are formed.

The sensor 40 may also be an antenna that measures electromagnetic waves from the inverter 10 or a partial discharge source as a parameter.
The configuration of sensors 40 and parameters is not limited to any particular configuration.

The sensor 40 transmits a voltage (analog signal) indicating the value of the measured parameter to the A/D converter 30.

The A/D converter 30 converts the analog signal from the sensor 40 into a digital signal. That is, the A/D converter 30 generates a digital signal indicating the value of the measured parameter. The A/D converter 30 transmits the generated digital signal to the information processing device 20. For example, the A/D converter 30 is an oscilloscope.

The information processing device detects partial discharge based on the digital signal from the A/D converter 30.

FIG. 2 is a block diagram showing an example of the configuration of the information processing device 20. As shown in FIG. 2, the information processing device 20 includes a processor 21, a ROM 22, a RAM 23, an NVM 24, a communication unit 25, an operation unit 26, and a display unit 27.

The processor 21, the ROM 22, the RAM 23, the NVM 24, the communication unit 25, the operation unit 26 and the display unit 27 are connected to each other via a data bus or the like.

In addition, the information processing device 20 may be provided with configurations other than those shown in FIG. 2 as necessary, or certain configurations may be excluded from the information processing device 20.

The processor 21 has the function of controlling the operation of the entire information processing device 20. The processor 21 may include an internal cache and various interfaces. The processor 21 realizes various processes by executing programs stored in advance in the internal memory, the ROM 22, or the NVM 24.

Note that some of the various functions realized by the processor 21 executing the program may be realized by a hardware circuit. In this case, the processor 21 controls the functions executed by the hardware circuit.

ROM 22 is a non-volatile memory in which control programs, control data, etc. are pre-stored. The control programs and control data stored in ROM 22 are pre-installed according to the specifications of information processing device 20. ROM 22 stores, for example, programs for controlling the circuit board of information processing device 20.

RAM 23 is a volatile memory. RAM 23 temporarily stores data being processed by processor 21. RAM 23 stores various application programs based on instructions from processor 21. RAM 23 may also store data necessary for executing application programs and execution results of application programs.

The NVM 24 is a non-volatile memory to which data can be written and rewritten. The NVM 24 is composed of, for example, a hard disk drive (HDD), a solid state drive (SSD), or a flash memory. The NVM 24 stores control programs, applications, various data, and the like according to the operational use of the information processing device 20.

The communication unit 25 is an interface for connecting to the A/D converter 30 or the like. That is, the communication unit 25 receives a digital signal from the A/D converter 30. For example, the communication unit 25 is an interface that supports a LAN (Local Area Network) connection or a USB (Universal Serial Bus) connection.

The operation unit 26 accepts various operation inputs from the user. The operation unit 26 transmits a signal indicating the accepted operation to the processor 21. For example, the operation unit 26 is composed of a keyboard, a numeric keypad, and a touch panel.

The display unit 27 displays various information under the control of the processor 21. For example, the display unit 27 is configured with a liquid crystal monitor. Note that, if the operation unit 26 is configured with a touch panel or the like, the display unit 27 may be formed integrally with the operation unit 26.

For example, the information processing device 20 may be a tablet PC, a desktop PC, or a notebook PC.

Next, the functions realized by the information processing device 20 will be described. The functions realized by the processor 21 are realized by the processor 21 executing a program stored in the internal memory, the ROM 22, the NVM 24, or the like.

First, the processor 21 has the function of measuring parameters using the sensor 40 for a predetermined period of time.

Here, the sensor 40 measures a parameter. The sensor 40 transmits an analog signal indicating the value of the measured parameter to the A/D converter 30. The A/D converter 30 converts the analog signal from the sensor 40 into a digital signal and transmits it to the information processing device 20.

The processor 21 receives a digital signal indicating the value of the parameter measured by the sensor 40 from the A/D converter 30 via the communication unit 25. The processor 21 receives the digital signal for a predetermined period (for example, about 1 ms to 1 s).

The processor 21 also has a function of counting pulses during a predetermined period.
Having measured the parameter over a given period of time, the processor 21 counts the pulses of the parameter over the given period of time, i.e. the processor 21 counts the pulses whose height exceeds a threshold value.

The processor 21 sets multiple thresholds and counts the pulses. For example, the processor 21 sets a predetermined threshold. When the predetermined threshold is set, the processor 21 counts the pulses whose wave height exceeds the threshold. When the pulses are counted, the processor 21 sets the next threshold. When the next threshold is set, the processor 21 similarly counts the pulses whose wave height exceeds the threshold. The processor 21 repeats the above operation to count the pulses at multiple thresholds.

Here, the processor 21 sets at least one threshold that is smaller than the pulse height of the background noise. That is, the processor 21 counts the pulses caused by the background noise.

The threshold values and the number of thresholds set by the processor 21 are not limited to a specific configuration.

The processor 21 stores in the RAM 23 or NVM 24 each threshold value and the number of pulses (the number of counted pulses) corresponding to the threshold value.

Next, an example of pulses counted by the processor 21 will be described.
First, an example of the number of pulses when no partial discharge occurs will be described.
Fig. 3 shows the values of parameters measured by the sensor 40 when no partial discharge is occurring. In Fig. 3, the horizontal axis shows time, and the vertical axis shows the value of the parameter (here, potential).

The processor 21 sets a predetermined threshold (e.g., 0.01) and counts the pulses. After counting the pulses, the processor 21 sets the next threshold (e.g., 0.02) and counts the pulses in the same manner. The processor 21 similarly sets thresholds up to a predetermined value (e.g., 0.16) and counts the pulses for each threshold.

Figure 4 shows the number of pulses at each threshold. In Figure 4, the horizontal axis shows the threshold and the vertical axis shows the number of pulses. In the example shown in Figure 4, the pulses are caused by background noise and inverter noise.

Inverter noise is noise generated by the inverter 10. For example, inverter noise is noise generated by the switching of each leg of the inverter element 4.

As shown in Figure 4, pulses counted with a relatively small threshold (e.g., on the order of 0.01 to 0.05) are caused by background noise. Also, the number of pulses due to background noise decreases linearly as the threshold increases.

Moreover, pulses counted with a relatively large threshold (for example, about 0.05 to 0.16) are caused by inverter noise, and the number of pulses due to inverter noise decreases at a gentle rate with respect to a relatively small threshold.
Therefore, the graph of the number of pulses when no partial discharge occurs is composed of two straight lines with different slopes.

Next, we will explain an example of the number of pulses when partial discharge occurs. For example, a sample simulating a busbar is inserted between busbars 1 to generate partial discharge.

Figure 5 shows the parameter values measured by the sensor 40 when partial discharge occurs. In Figure 5, the horizontal axis shows time, and the vertical axis shows the parameter value (here, potential).

As described above, the processor 21 sets a predetermined threshold (e.g., 0.01) and counts the pulses. After counting the pulses, the processor 21 sets the next threshold (e.g., 0.02) and counts the pulses in the same manner. The processor 21 similarly sets thresholds up to a predetermined value (e.g., 0.16) and counts the pulses for each threshold.

Figure 6 shows the number of pulses at each threshold. In Figure 6, the horizontal axis shows the threshold and the vertical axis shows the number of pulses. In the example shown in Figure 6, the pulses are caused by partial discharge, background noise, and inverter noise.

Pulses caused by partial discharges are counted with a medium threshold (0.03 to 0.1).

As shown in Figure 6, the graph shows the number of pulses due to partial discharge superimposed on the number of pulses due to background noise and inverter noise.

As a result, the graph of the number of pulses when partial discharges are occurring will have a higher middle part than the graph of the number of pulses when partial discharges are not occurring.

The processor 21 also has the function of determining whether a partial discharge has occurred based on the number of counted pulses.

The processor 21 determines whether a pulse due to partial discharge is superimposed on the counted pulses.

For example, the processor 21 calculates the correlation coefficient between the threshold and the number of pulses according to the following formula:

Here, xi represents the threshold value, and yi represents the number of pulses.

After calculating the correlation coefficient, the processor 21 determines whether partial discharge is occurring based on the correlation coefficient.

As mentioned above, when no partial discharge is occurring, the pulse count graph consists of two straight lines. As a result, when the threshold and pulse count are linearly approximated, the correlation coefficient becomes a relatively small value.

On the other hand, when partial discharges are occurring, the graph of the number of pulses has a higher middle part than the graph of the number of pulses. As a result, a linear approximation of the threshold and the number of pulses is closer to a straight line than when partial discharges are not occurring. Therefore, the correlation coefficient is higher than when partial discharges are not occurring.

Therefore, when the correlation coefficient is greater than a predetermined threshold, the processor 21 determines that a partial discharge is occurring. Note that the threshold is not limited to a specific value.

The processor 21 may also normalize each pulse number by the maximum number of pulse numbers corresponding to each threshold value before calculating the correlation coefficient.

The processor 21 may also determine whether a partial discharge is occurring based on the change in the correlation coefficient over time. For example, the processor 21 determines that a partial discharge is occurring when the correlation coefficient increases (for example, when the increase in a specified period of time is equal to or greater than a specified threshold value).

Processor 21 may also determine whether partial discharge is occurring based on the sum of the number of pulses at each threshold. For example, processor 21 determines that partial discharge is occurring when the sum exceeds a predetermined threshold. Processor 21 may also determine that partial discharge is occurring when the sum increases (for example, when the increase in the sum over a predetermined period is equal to or greater than a predetermined threshold).

The method by which the processor 21 determines the occurrence of partial discharge is not limited to any particular method.

When it is determined that a partial discharge has occurred, the processor 21 outputs a warning indicating that a partial discharge has occurred. For example, the processor 21 displays a warning on the display unit 27. The processor 21 may also transmit information indicating that a partial discharge has occurred to an external device via the communication unit 25 or the like.

Next, an example of the operation of the information processing device 20 will be described.
FIG. 7 is a flowchart for explaining an example of the operation of the information processing device 20. As shown in FIG.

First, the processor 21 of the information processing device 20 measures a parameter for a predetermined period of time using the sensor 40 (S11). After measuring the parameter, the processor 21 counts pulses using multiple thresholds (S12).

After counting the pulses using multiple thresholds, the processor 21 calculates a correlation coefficient between the thresholds and the number of pulses (S13). After calculating the correlation coefficient, the processor 21 determines whether a partial discharge is occurring based on the calculated correlation coefficient (S14).

If it is determined that partial discharge has occurred (S14, YES), the processor 21 outputs a warning (S15).

If it is determined that no partial discharge has occurred (S14, NO), or if a warning has been output (S15), the processor 21 returns to S11.

The processor 21 may also determine whether partial discharge has occurred based on parameter values previously measured by another device.

The detection system 100 may also detect partial discharges occurring in devices other than the inverter 10. The objects for which the detection system 100 detects partial discharges are not limited to a specific configuration.

The processor 21 may also set the period for measuring the parameters according to the operation input to the operation unit 26.

The detection system configured as described above sets multiple thresholds and counts pulses whose wave height exceeds each threshold. The detection system detects partial discharges based on the correlation coefficient between the thresholds and the number of pulses. Therefore, the detection system can detect partial discharges even when the period of inverter noise and the period in which partial discharges occur match. As a result, the detection system can effectively detect partial discharges.

Although some embodiments of the present invention have been described, 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 forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims.
[Appendix 1]
Measure the parameters related to the discharge generated in the device,
Counting pulses of said measured parameter;
The partial discharge detection method includes outputting a warning indicating that a discharge is occurring in the device based on the number of pulses counted.
[Appendix 2]
Set multiple thresholds,
2. The partial discharge detection method according to claim 1, wherein counting the pulses comprises counting pulses whose heights exceed the respective threshold values.
[Appendix 3]
Calculating a correlation coefficient between the threshold value and the number of pulses counted;
3. The partial discharge detection method according to claim 2, wherein outputting the warning is based on the correlation coefficient.
[Appendix 4]
4. The partial discharge detection method according to claim 3, wherein outputting the warning is performed when the correlation coefficient is greater than a predetermined threshold.
[Appendix 5]
4. The partial discharge detection method according to claim 3, wherein outputting the warning is based on a change in the correlation coefficient over time.
[Appendix 6]
5. The partial discharge detection method according to claim 1, wherein the device is a power converter.
[Appendix 7]
7. The partial discharge detection method according to claim 1, wherein the parameter is the potential of a panel surface of the device.
[Appendix 8]
7. The partial discharge detection method according to claim 1, wherein the parameter is a current flowing through a ground wire connected to the device.
[Appendix 9]
7. The partial discharge detection method according to claim 1, wherein the parameter is an electromagnetic wave generated by the device.
[Appendix 10]
10. The partial discharge detection method according to any one of claims 1 to 9, wherein outputting the warning is based on an increase in the number of pulses.

1 (1a to 1c)...busbar, 2 (2a and 2b)...busbar, 4...inverter element, 4a...surface insulating layer, 4b...interlayer insulating layer, 5...snubber unit, 5a...snubber element, 6...fixing screw, 10...inverter, 20...information processing device, 21...processor, 22...ROM, 23...RAM, 24...NVM, 25...communication unit, 26...operation unit, 27...display unit, 30...A/D converter, 40...sensor, 100...detection system.

Claims (9)

Measure the parameters related to the discharge generated in the device,
Set multiple thresholds,
Counting pulses of said measured parameter;
A method for outputting a warning indicating that a discharge is occurring in the device based on the number of pulses counted, comprising:
The method for detecting partial discharge , wherein counting the pulses comprises counting pulses whose heights exceed the respective threshold values. Calculating a correlation coefficient between the threshold value and the number of pulses counted;
The partial discharge detection method according to claim 1 , wherein outputting the warning comprises outputting the warning based on the correlation coefficient. The partial discharge detection method according to claim 2 , wherein outputting the warning comprises outputting the warning when the correlation coefficient is greater than a predetermined threshold value. The partial discharge detection method according to claim 2 , wherein outputting the warning comprises outputting the warning based on a change over time in the correlation coefficient. The partial discharge detection method according to claim 1 , wherein the device is a power converter. 6. The partial discharge detection method according to claim 1, wherein the parameter is a potential of a surface of the device. 6. The method of claim 1, wherein the parameter is a current flowing through a ground conductor connected to the device. The partial discharge detection method according to claim 1 , wherein the parameter is an electromagnetic wave generated by the device. 9. The partial discharge detection method according to claim 1, wherein outputting the warning comprises outputting the warning based on an increase in the number of the pulses.