JP7844845B2 - Wire break detection device, wire break detection method, and program - Google Patents

Description

This invention relates to a wire break detection device, a wire break detection method, and a program.

Power transformers used in substations are generally equipped with on-load tap changers to adjust the voltage during operation (under load conditions) (see, for example, Patent Document 1). An on-load tap changer is a device that switches between transformer winding taps with different generated electromotive forces while the transformer is operating. The on-load tap changer must switch without interruption (no power outage), and bridging occurs between different taps at the moment of switching. When bridging occurs, an excessive bridging current (crosscurrent) flows through the transformer windings and the tap changer, leading to excessive wear or damage to the switching contacts, and stress on the windings due to excessive stress.

To avoid this, on-load tap changers employ a resistance switching method in which a current-reducing resistor is temporarily inserted at the timing of tap bridging to suppress bridging current. The current-reducing resistor is installed near the movable contact of the on-load tap changer, which is the only mechanically moving part in the static transformer. Because it is susceptible to mechanical vibration and shock, repeated operation of the tap changer or aging can potentially cause the resistance element to break.

Under normal transformer operation, no current flows through this current-limiting resistor. Even if a break occurs, it is difficult for commonly used transformer internal fault detection protection relay devices, such as ratio-operated relays, to detect the break. The current-reducing resistor is housed, for example, inside the transformer tank, and its condition cannot be visually checked during operation, nor can it be checked using electrical measuring instruments. Furthermore, even if the resistance value is measured externally during inspection, it is difficult to estimate the state of deterioration unless a break occurs. Regarding standard specifications for transformer internal fault detection protection relay devices, there is the standard described in Non-Patent Document 1.

If a current-reducing resistor breaks, a momentary interruption in the supply voltage may occur when tap switching is performed under load to adjust the voltage. However, this often does not immediately lead to an internal transformer failure resulting in a power outage. Nevertheless, because the tap switching contacts switch currents far exceeding their intended operating capacity, problems such as significant wear and damage to the contacts and the formation of sludge in the oil can accumulate, potentially leading to a serious internal transformer failure and a power outage. If a current-reducing resistor breaks, it is necessary to immediately stop the operation of the transformer, and a means of detecting the current-reducing resistor break is required.
The presence or absence of open circuits in the current-reducing resistor of the under-load tap changer is checked by a low-voltage test with the transformer shut down. In this test method, the transformer is shut down, a low voltage is applied to the primary side of the transformer, and the tap changer is performed. The presence or absence of momentary interruptions in the secondary side voltage of the transformer is visually checked using a needle-type voltmeter or similar device.

Japanese Patent Publication No. 2017-221040

"Ratio Differential Relay for Power Equipment Protection, JEC-2515-2005," Standard Specification of the Electrical Standards Committee of the Institute of Electrical Engineers of Japan, IEEJ, 2005.

However, conventional technology could not detect a break in the current-reducing resistor of the on-load tap changer during transformer operation. Furthermore, continuing transformer operation with a broken current-reducing resistor would lead to a serious transformer accident.

This invention has been made in view of the above-mentioned problems, and aims to provide a wire break detection device, a wire break detection method, and a program that enable detection of a wire break in a current reducing resistor during transformer operation.

A wire break detection device according to one aspect of the present invention comprises: a first detection unit that detects at least one of the primary current of a transformer, the second harmonic component of the primary current of the transformer, the secondary voltage of the transformer, and an acoustic signal near the transformer body; a second detection unit that detects at least one of the switching command for the switch and the current or voltage flowing to the motor for switching the switch; a detection processing unit that compares the first detection result detected by the first detection unit with a threshold value to make a determination or detection; a detection processing unit that outputs a tap switching operation signal based on the second detection result detected by the second detection unit; and a processing unit that determines and displays whether the current reducing resistor connected to the transformer is normal or abnormal based on the determination or detection result output by the detection processing unit and the tap switching operation signal.

Furthermore, in a wire break detection device according to one aspect of the present invention, the detection processing unit may calculate the moving average of the primary current before the tap switching operation, calculate the minimum value of the primary current during the tap switching operation, and determine that a momentary interruption has occurred in the primary current when the moving average value of the primary current is greater than the load current detection level and the minimum value of the primary current is less than the first threshold, thereby issuing an abnormality alert indicating that the current reducing resistor is abnormal.

Furthermore, in a wire break detection device according to one aspect of the present invention, the detection processing unit may calculate the moving average of the secondary voltage before the tap switching operation, calculate the minimum value of the secondary voltage during the tap switching operation, and if the difference between the moving average of the secondary voltage and the minimum value of the secondary voltage is greater than a second threshold, the processing unit may determine that the secondary voltage is momentarily interrupted and issue an abnormality notification indicating that the current reducing resistor is abnormal.

Furthermore, in a wire break detection device according to one aspect of the present invention, the detection processing unit may calculate a moving average of the magnitude of the acoustic signal before the tap switching operation, detect the maximum value of the magnitude of the acoustic signal after the tap switching operation, and determine that an acoustic abnormality exists when the difference between the level of the acoustic signal and the moving average of the level of the acoustic signal is greater than a third threshold, thereby issuing an abnormality notification indicating that the current reducing resistor is abnormal.

Furthermore, in a wire break detection device according to one aspect of the present invention, the detection processing unit may calculate the maximum value of the second harmonic of the primary current, and if the maximum value of the second harmonic is greater than the fourth threshold during or after the tap switching operation, the processing unit may determine that the second harmonic is abnormal and issue an abnormality notification indicating that the current reducing resistor is abnormal.

Furthermore, in a wire break detection device according to one aspect of the present invention, the processing unit may count the number of occurrences of the determined determination result a predetermined number of times, and if the count value is equal to or greater than a fifth threshold, it may determine whether the current reducing resistance is normal or abnormal and issue a notification.

Furthermore, in a wire break detection device according to one aspect of the present invention, the processing unit may acquire the switching command output by the second detection unit for a period equivalent to the switching time.

A wire break detection method according to one aspect of the present invention involves a first detection unit detecting at least one of the following: the primary current of the transformer, the second harmonic component of the primary current of the transformer, the secondary voltage of the transformer, and an acoustic signal near the transformer body; a second detection unit detecting at least one of the following: a switching command for the switch and the current or voltage flowing to the motor for switching the switch; a detection processing unit comparing the first detection result detected by the first detection unit with a threshold value to make a determination or detection; a second detection unit outputting a tap switching operation signal based on the second detection result detected by the second detection unit; and a processing unit determining and displaying whether the current reducing resistor connected to the transformer is normal or abnormal based on the determination or detection result output by the detection processing unit and the tap switching operation signal.

A program according to one aspect of the present invention causes a computer to detect at least one of the following as a first detection result: the primary current of a transformer, the second harmonic component of the primary current of the transformer, the secondary voltage of the transformer, and an acoustic signal near the transformer body; to detect at least one of the following as a second detection result: a switching command for the switch and the current or voltage flowing to the motor for switching the switch; to compare the first detection result with a threshold value to make a determination or detection; to output a tap switching operation signal based on the second detection result; and to determine and indicate whether the current reducing resistor connected to the transformer is normal or abnormal based on the determination or detection result output by the detection processing unit and the tap switching operation signal.

According to embodiments of the present invention, if a break occurs in the current-reducing resistor, it can be detected during transformer operation.

This figure shows an example configuration of a wire break detection system according to an embodiment. This figure shows an example configuration of a wire break detection device according to an embodiment. This is an example of the configuration of a three-phase transformer for power distribution. This figure shows examples of the operation of each contact under normal conditions and examples of the operation of each contact when the current reducing resistor is disconnected. This is a timing chart for tap switching during normal operation. This is a timing chart for tap switching when the current reducing resistor RA of phase C is broken, the contacts interrupt the current, and the load has impedance characteristics. This is a timing chart for tap switching when the current reducing resistor RA of phase C is broken, the contacts interrupt the current, and the load has a large voltage source. This figure shows an example of the events that occur and detection methods when tap switching is performed while the current reducing resistor is disconnected according to the embodiment. This is a flowchart of the processing procedure performed by the wire break detection device according to the embodiment. This figure shows an example of the external appearance of a wire break detection device according to an embodiment.

The embodiments of the present invention will be described below with reference to the drawings. Note that in the drawings used in the following description, the scale of each component has been appropriately adjusted to ensure that each component is recognizable.

[Configuration of the wire break detection system]
Figure 1 shows an example of the configuration of the wire break detection system according to this embodiment. The wire break detection system 1 comprises a power supply busbar 11, a load-side tap-changing transformer 12, a load-side busbar 13, a voltage detection unit 14, an acoustic detection unit 15, a content detection unit 16, a current detection unit 17, a motor current-voltage detection unit 18, a tap-changing motor-operated mechanism 19, a command detection unit 22, a processing unit 29, and an operation information output unit 24. The tap-changing motor-operated mechanism 19 comprises a drive motor 20 and a motor power supply 21. Note that the processing unit 29 in Figure 1 corresponds to the example of the detection processing unit 23 and processing unit 25 in Figure 2.

The load-operated tap-changing transformer 12 has one end connected to the power supply busbar 11 and the other end connected to the load-side busbar 13.

The voltage detection unit 14 is a sensor that detects voltage and is connected, for example, to the load-side busbar 13.

The acoustic detection unit 15 is a sensor that detects vibrations or acoustic signals, and includes, for example, a vibration sensor or an acoustic microphone.

The content detection unit 16 is a sensor that, for example, detects the second harmonic component of the current flowing on the secondary side of the primary-side current transformer 121 of the transformer 12 connected to the power supply busbar 11, using a well-known method.

The current detection unit 17 is a sensor that detects the current value flowing on the secondary side of the primary-side current transformer 121 of the transformer 12, which is connected to the power supply bus 11, for example.

The motor current/voltage detection unit 18 is a sensor that detects whether the motor power supply 21 for motor drive is supplying current or voltage to the drive motor 20. While the motor power supply 21 is supplying current or voltage to the drive motor 20, it outputs an LTC operation signal indicating that tap switching is in progress.

The command detection unit 22 is a sensor that detects and outputs an operation command when an operation command is issued from the control device (not shown) to the tap changer electric operation mechanism 19.

The processing unit 29 determines whether the current-reducing resistor built into the load-operated tap changer is open based on the detection results output by each detection unit, and outputs the determination result to the operation information output unit 24. The determination method will be described later. The processing unit is, for example, a CPU (Central Processing Unit).

The operation information output unit 24 includes, for example, a wired communication circuit, a wireless communication circuit, or an interface circuit. The operation information output unit 24 outputs the determination result to an external device via wired or wireless connection. The external device may be, for example, a tablet terminal, smartphone, personal computer, or dedicated terminal.

[Example of a wire break detection device configuration]
Next, we will describe an example of the configuration of the wire break detection device 2.
Figure 2 shows an example of the configuration of a wire break detection device according to this embodiment. As shown in Figure 2, the wire break detection device 2 includes, for example, a detection unit 100, a detection processing unit 23, a processing unit 25, a storage unit 26, a display unit 27, and an operation unit 28.

The detection unit 100 includes, for example, a first detection unit 110 and a second detection unit 120.
The first detection unit 110 includes, for example, a content detection unit 16, a current detection unit 17, a voltage detection unit 14, and an acoustic detection unit 15.
The second detection unit 120 includes, for example, a motor current voltage detection unit 18 and a command detection unit 22.

The detection processing unit 23 includes, for example, a content determination unit 231, a current interruption detection unit 232, an instantaneous voltage drop detection unit 233, an acoustic increase detection unit 234, a one-shot circuit 235, and an OR circuit 236.

The processing unit 25 includes, for example, an OR circuit 251 and a frequency determination unit 252. Note that the detection processing unit 23 and the processing unit 25 may be, for example, a single CPU (Central Processing Unit).

The content determination unit 231 detects and outputs a value if, during or after tap switching operation, the second harmonic current content of the transformer power supply side current exceeds the second harmonic content setting value of 2fd (%).

The current interruption detection unit 232 detects and outputs a signal when the current value during the tap switching operation drops to or below the set value I1s (A), while the average current value before the tap switching operation is equal to or greater than the set value I1a (A).

The instantaneous voltage drop detection unit 233 detects and outputs a voltage drop if the current voltage continuously drops by a set voltage drop amount of △V (V) or more for a period of duration set to △T1 (ms) or more, relative to the voltage moving average value before the tap switching operation.

The sound level increase detection unit 234 detects and outputs a signal when the sound level obtained by filtering the vibration sensor or acoustic microphone output through a low-pass filter exceeds the sound level increase amount dSL (dB) after the tap switching operation, relative to the moving average sound level before the tap switching operation.

The one-shot circuit 235 outputs a high-level signal, for example, to the OR circuit 236 for a period equivalent to the switching time of the command signal, in response to the detection result of the command detection unit 22. That is, when an operation command is issued to the tap changer, the one-shot circuit 235 outputs an LTC operation signal for a certain period (one shot) equivalent to the time the tap changer is operating.

The OR circuit 236 outputs one of the detection results from the motor current/voltage detection unit 18 and one of the outputs from the one-shot circuit 235 to the frequency determination unit 252. The OR circuit 236 then outputs the detection results from the motor current/voltage detection unit 18 and one of the outputs from the one-shot circuit 235 as an LTC operation signal to the content determination unit 231, the current interruption detection unit 232, the instantaneous voltage drop detection unit 233, and the sound increase detection unit 234.

The OR circuit 251 selects one or more elements from the results of the content determination unit 231, the current interruption detection unit 232, the instantaneous voltage drop detection unit 233, and the sound increase detection unit 234, and outputs them to the frequency determination unit 252.

The frequency determination unit 252 determines whether the detection frequency is normal or abnormal based on the output of the OR circuit 251 and the output of the OR circuit 236. The frequency determination unit 252 outputs the determination result to an external device.

The detection processing unit 23 stores the operation time in the storage unit 26. The detection processing unit 23 also stores each judgment result in the storage unit 26. The detection processing unit 23 also stores the current value, voltage value, and sound level in the storage unit 26. The operation time and each judgment will be described later.

The memory unit 26 stores the operation time. The memory unit 26 also stores each judgment result.

The display unit 27 is, for example, a liquid crystal display device, an organic EL (electroluminescence) display, a lamp, etc. The display unit 27 displays, for example, the operating status of the wire break detection device 2, the current time, etc.

The operation unit 28 is, for example, a mechanical button switch, such as a judgment start button, judgment end button, or setting button for the wire break detection device 2.

Note that the configuration example shown in Figure 2 is just one example and is not limited to this. The wire break detection device 2 does not need to have all of the detection units described above; it may have some of them. Furthermore, the wire break detection device 2 may also include an operation information output unit 24 (Figure 1).

[Example of tap switching operation]
Here, we will explain an example of tap switching operation in normal and abnormal conditions.
Figure 3 shows an example configuration of a three-phase transformer for power distribution. In the example in Figure 3, the voltage on the power supply side 302 of the three-phase transformer 301 is, for example, 66 kV, and the voltage on the load side 303 is, for example, 6 kV. The load 304 can be, for example, an inductive component L, a resistive component R, a capacitive component C, a rotating machine, an inverter, etc.

Furthermore, the tap changer 311 enclosed by the dashed circle 311 in the three-phase transformer 301 has a configuration as shown by the dashed circle 312 when magnified. For example, tap N in the tap changer 311 is connected to one end of contact HA and one end of contact WA. Tap M is connected to one end of contact WB and one end of contact HB. The other end of contact WA is connected to one end of current-reducing resistor RA. The other end of contact WB is connected to one end of current-reducing resistor RB. The other end of contact HA is connected to the other end of current-reducing resistor RA, the other end of current-reducing resistor RB, the other end of contact HB, and the tap changer electric operating mechanism 19 (Figure 1).

Figure 4 shows examples of the operation of each contact under normal conditions and examples of the operation of each contact when the current reducing resistor is open. The area g351 enclosed by the dashed line represents the conduction movement of the contacts when switching from tap N to tap M under normal conditions. The horizontal axis represents time. In this case, since at least one contact is in contact at any given time, no momentary interruption of current occurs.

The area g352 enclosed by the dashed line represents the conduction movement of the contacts during the switch from tap N to tap M when the current-reducing resistor RA is disconnected and contact HA interrupts the current. The horizontal axis represents time. In this case, as shown in the dashed rectangle g353, the current-reducing resistor RA, which is connected in series with contact WA, is disconnected. Therefore, a conduction path is not formed through contact WA, and there is a period of time when no contacts are in contact, resulting in a momentary interruption of current.

The area g354 enclosed by the dashed line represents the conduction of the contacts during the switch from tap N to tap M when the current-reducing resistor RA is disconnected and contact HA is bridged. The horizontal axis represents time. In this case, as shown in the dashed rectangle g355, the current-reducing resistor RA, which is connected in series with contact WA, is disconnected, so a conduction path through contact WA is not formed. However, because contact HA is bridged during the period when current should be flowing through contact WA, no momentary interruption of current occurs.

This explains the difference between cases where a tap switching contact interrupts the current when a current reducing resistor breaks, and cases where it fails to interrupt the current and causes a contact bridging.
In power distribution transformers, the current switching capacity of the tap switching contacts is equivalent to the rated current (above the normal load current). However, the voltage that can be interrupted (recovery voltage) is only a few percent of the main circuit's rated voltage. Under these conditions, high-frequency switching on the order of 200,000 times is possible. Furthermore, for a small number of switching cycles, the switching capacity exceeds the operating duty. Also, since the contacts are oil-immersed contacts, the recovery voltage that can be interrupted increases as the load current decreases.

If the transformer load were a purely resistive load, the recovery voltage would be approximately 86% of the main circuit voltage. However, actual loads include rotating machinery such as induction motors and distributed power sources such as solar inverters. Even if the circuit is momentarily interrupted, an electromotive force exists on the load side, effectively reducing the recovery voltage further. Furthermore, while induction motors are generally considered to not generate electromotive force, even after a power outage (excitation current interruption), the rotating magnetic field remains, causing electromotive force to be generated for several cycles. It should be noted that this load-side electromotive force varies significantly depending on regional conditions and time of day, making it impossible to calculate a precise figure.

In a case like the region g352 enclosed by the dashed line in Figure 4, when the current-reducing resistor is broken, if it is a resistive load, the recovery voltage of the contact will be about 86% of the main circuit's rated voltage, which far exceeds the operating duty. However, if the electromotive force on the load side is taken into consideration, the recovery voltage will decrease significantly.
Furthermore, because the load current is smaller under light load conditions due to the load curve, the likelihood of current interruption increases. A load curve is a curve that represents the change in the amount of electricity used over a period of time, such as a day or a year.
Furthermore, in cases like the region g354 enclosed by the dashed line in Figure 4, if the current cannot be interrupted and the contacts become arc-bridged, no momentary interruption will occur in the main circuit. The excitation current will also not be interrupted.

The parameters related to current interruption are the load current, load characteristics, and tap changer contact operation timing (relationship with current phase).

[Example of a timing chart for tap switching]
Next, we will explain an example of a timing chart for tap switching.
Figure 5 is a timing chart for tap switching under normal conditions. In Figure 5, the horizontal axis represents time. From top to bottom, the chart shows the tap switching command (g401), tap state (g402), drive motor current (g403), contact operation state (g404), noise level (g405), transformer primary current A phase (g406), transformer primary current B phase (g407), transformer primary current C phase (g408), second harmonic content of the transformer primary current (g409), and transformer secondary voltage (g410). Note that even if the current reducing resistor is broken and a bridge occurs, the situation is the same as in Figure 5, except for the contact operation state.

The example in Figure 5 shows the case where a lift/lower command, which is a tap switching command, is input from an external device at time t11. In this case, no current flows to the drive motor 20 until time t11 (g403), and the acoustic components detected by the acoustic detection unit 15 include the excitation sound, which is a characteristic sound emitted by the transformer during excitation (g405).

During the period approximately t11 to t13, current flows through the drive motor 20 (g403), the tap state switches from tap N to tap M (g402), and the contact operation state switches to contacts HA, WA, WB, and HB (g404).

During the period from time t11 to t12, the acoustic components detected by the acoustic detection unit 15 include motor noise. During the period from time t12 to t13, the acoustic components detected by the acoustic detection unit 15 include a switching sound, which is a distinctive sound similar to the sound of metal striking during switching.

Furthermore, under normal conditions and in the case of a bridge due to a break in the current reducing resistor, the second harmonic content (g409) of the primary current of the transformer is almost zero, and there are no significant changes in the primary current A phase (g406), primary current B phase (g407), primary current C phase (g408), and secondary voltage (g410) of the transformer. Also, from time t13 onward, the acoustic component detected by the acoustic detection unit 15 is the excitation sound.

Figure 6 is a timing chart for tap switching when the current reducing resistor RA of phase C is broken, the contacts interrupt the current, and the load has impedance characteristics. In Figure 6, the horizontal axis represents time. From top to bottom, the graphs show the tap switching command (g451), tap state (g452), drive motor current (g453), contact operation state (g454), noise level (g455), transformer primary current phase A (g456), transformer primary current phase B (g457), transformer primary current phase C (g458), second harmonic content of the transformer primary current (g459), and transformer secondary voltage (g460).

In this case as well, until the lifting/lowering command is input from the external device at time t21, no current flows to the drive motor 20 (g453), and the acoustic component detected by the acoustic detection unit 15 includes the excitation sound (g455).

During the period from approximately time t21 to t26, current flows through the drive motor 20 (g453), the tap state switches from tap N to tap M (g452), and the contact operation state switches to contacts HA, WA, WB, and HB (g454).

During the period from time t21 to t25, the acoustic components detected by the acoustic detection unit 15 include motor noise. During the period from time t22 to t25, the acoustic components detected by the acoustic detection unit 15 include switching noise. Furthermore, from time t24 onward, the acoustic components detected by the acoustic detection unit 15 include inrush noise, a characteristic sound that occurs during inrush excitation.

Then, during the period from time t23 to t24, a momentary interruption occurs in the C phase of the transformer's primary current (g458). During the period from time t23 to t24, a momentary voltage drop occurs in the transformer's secondary voltage (g460). Furthermore, from time t24 onward, an inrush current is superimposed on the transformer's primary current A phase (g456), B phase (g457), and C phase (g458). In addition, in response to the generation of the inrush current, a second harmonic is introduced into the transformer's primary current (g459).

Figure 7 is a timing chart for tap switching when the current reducing resistor RA of phase C is broken, the contacts interrupt the current, and the load has a large voltage source. In Figure 7, the horizontal axis represents time. From top to bottom, the graphs show the tap switching command (g501), tap state (g502), drive motor current (g503), contact operation state (g504), noise level (g505), transformer primary current phase A (g506), transformer primary current phase B (g507), transformer primary current phase C (g508), second harmonic content of the transformer primary current (g509), and transformer secondary voltage (g510).

In this case as well, until the lifting/lowering command is input from the external device at time t31, no current flows to the drive motor 20 (g503), and the acoustic component detected by the acoustic detection unit 15 includes the excitation sound (g505).

During the period from approximately time t31 to t37, current flows through the drive motor 20 (g503), the tap state switches from tap N to tap M (g502), and the contact operation state switches to contacts HA, WA, WB, and HB (g504).

During the period from time t31 to t35, the sound components detected by the sound detection unit 15 include motor noise. During the period from time t32 to t35, the sound components detected by the sound detection unit 15 include switching noise. From time t35 onward, the sound components detected by the sound detection unit 15 include excitation noise.

Then, during the period from time t33 to t34, a momentary interruption occurs in the C phase of the transformer's primary current (g458). During the period from time t33 to t34, fluctuations appear in the A phase (g506) and B phase (g507) of the transformer's primary current. During the period from time t33 to t35, voltage fluctuations occur in the transformer's secondary voltage (g460). Note that the second harmonic content of the transformer's primary current (g459) is almost zero.

Note that the timings, currents, voltages, noise levels, etc., shown in Figures 5 to 7 are examples only and are not limited to these.

[Detection Method]
If a current-reducing resistor is disconnected and tap switching is performed under load, there are cases where the tap switching contact will interrupt the current and cases where it will not.
Figure 8 shows an example of the events that occur and detection methods when tap switching is performed in the current-reducing resistor open state according to this embodiment.

When the phenomenon is "a momentary voltage drop occurs on the transformer load side due to a momentary interruption of the transformer current," the detection method is as follows: "The voltage monitoring circuit on the transformer load side is equipped with a voltage detection unit 14 and a momentary voltage drop detection unit 233, and the voltage drop width ΔV (V) and duration ΔT1 (ms) are set as thresholds."

When the phenomenon occurs where "the excitation current is momentarily interrupted, causing the iron core to become biased and magnetic flux saturation to occur, resulting in the flow of an excitation inrush current containing a second harmonic current," the detection method is as follows: "A content detection unit 16 and a content determination unit 231 are provided on the transformer power supply side to detect the second harmonic and determine its content, and a second harmonic content setting value of 2fd (%) is set as the threshold value."

When the phenomenon is "a loud excitation noise (inrush noise) is generated due to the excitation inrush current," the detection method is to "install an acoustic detection unit 15 using a vibration sensor or acoustic microphone near the transformer tank." Furthermore, the detection method involves "equipping the acoustic increase detection unit 234 with a low-pass filter to increase its sensitivity to excitation noise, and setting the threshold value as the increase in the sound level after switching relative to the moving average of the sound level before switching, dSL (dB)."

When the phenomenon is "a momentary interruption of the transformer current," the detection method is as follows: "A current detection unit 17 and a current interruption detection unit 232 are provided on the transformer power supply side, and when the moving average value of the current before switching is I1a (A) or higher, the minimum value of the current during switching, I1s (A), is set as the threshold."

If one or more of the above-described phenomena are detected, there is a possibility of a current-reducing resistor being disconnected. However, these phenomena can also occur during substation operation or during system faults. Therefore, in this embodiment, unnecessary operation is prevented by determining that a current-reducing resistor is disconnected only when one or more of these phenomena occur during or immediately after tap switching.

Furthermore, load-operated tap changers generally operate several to several dozen times a day. Therefore, in this embodiment, an operation counter for these phenomena is added, and if the number of detected tap change operations exceeds a set detection limit (for example, two or more out of ten), a disconnection is detected, thereby preventing unnecessary operation (frequency monitoring).

[Processing Procedure]
Next, an example of the processing procedure performed by the wire break detection device 2 will be explained.
Figure 9 is a flowchart of the processing procedure performed by the wire break detection device according to this embodiment.

(Step S1) The current interruption detection unit 232 calculates the moving average of the three-phase primary currents (Ia, Ib, Ic) detected by the current detection unit 17. The instantaneous voltage drop detection unit 233 calculates the moving average of the three-phase load-side voltages (Vab, Vbc, Vca) detected by the voltage detection unit 14. The sound increase detection unit 234 calculates the moving average SDb of the sound level detected by the sound detection unit 15.

(Step S2) The motor current/voltage detection unit 18 determines whether or not motor current has been detected based on the detection result. The motor current/voltage detection unit 18 determines that motor current has been detected if the motor current is equal to or greater than a predetermined value, and determines that motor current has not been detected if the motor current is less than the predetermined value. If the motor current/voltage detection unit 18 determines that motor current has been detected (Step S2; YES), it proceeds to the process in Step S3. If the motor current/voltage detection unit 18 determines that motor current has not been detected (Step S2; NO), it returns to the process in Step S1.

(Step S3) The detection processing unit 23 stores the operation time in the storage unit 26. The detection processing unit 23 obtains the operation time, for example, via a network.

(Step S4) The current interruption detection unit 232 calculates the minimum values (Ia0, Ib0, Ic0) of the three-phase primary current during the tap switching operation when the moving average value of the current before the tap switching operation is equal to or greater than the set value I1a (A), and detects and outputs when the current value during the tap switching operation drops to or less than the set value I1s (A). The instantaneous voltage drop detection unit 233 calculates the minimum values (Vab0, Vbc0, Vca0) of the three-phase load-side voltage. The instantaneous voltage drop detection unit 233 detects and outputs when the current voltage drops by a set value △V (V) or more for a period of duration set value △T1 (ms) or more relative to the moving average value of the voltage before the tap switching operation. The content determination unit 231 calculates the maximum values (2fa0, 2fb0, 2fc0) of the second harmonic components of the three-phase current. The content determination unit 231 detects and outputs a value if, during tap switching operation, the second harmonic current content of the calculated transformer power supply side current exceeds the second harmonic content setting value of 2fd (%).

(Step S5) The motor current/voltage detection unit 18 determines whether or not motor current has been detected based on the detection result. If the motor current/voltage detection unit 18 determines that motor current has been detected (Step S5; YES), it returns to the process of Step S1. If the motor current/voltage detection unit 18 determines that motor current has not been detected (Step S5; NO), it proceeds to the process of Step S6.

(Step S6) The sound increase detection unit 234 waits for the confirmation time TW. During tap switching, the sound of tap switching (hereinafter referred to as "tap switching sound") is superimposed on the transformer's excitation sound, increasing the sound level. Therefore, in this embodiment, the confirmation time TW is defined as the period from the completion of the tap switching operation until the tap switching sound falls below a predetermined level. In this embodiment, processing is stopped and the unit waits during this confirmation time, and the sound level SDa is calculated at the timing when only the transformer's excitation sound remains. The confirmation time TW is, for example, a few seconds after the drive motor stops.

(Step S7) The sound increase detection unit 234 calculates the sound level SDa, which is the moving average of the sound levels before switching, after the confirmation time TW, and after switching.

(Step S8) The frequency determination unit 252 performs a primary current interruption determination. The frequency determination unit 252 determines that the primary current is interrupted if the following conditions are met.
Conditions: Moving average value of the three-phase primary currents (Ia, Ib, Ic) > Load current detection level AND Minimum value of the three-phase primary currents (Ia0, Ib0, Ic0) < First threshold. In addition, the frequency determination unit 252 performs a voltage interruption determination on the load side. The frequency determination unit 252 determines that the voltage on the load side is interrupted if the following conditions are met.
Condition: Moving average value of the three-phase voltages - minimum value (Vab - Vab0, Vbc - Vbc0, Vca - Vca0) > second threshold. In addition, the frequency determination unit 252 performs sound level determination. The frequency determination unit 252 determines that there is an abnormality if the following conditions are met.
Condition: Sound level SDa - Moving average value of sound level SDb > Third threshold. In addition, the frequency determination unit 252 performs a second harmonic detection determination of the current. The frequency determination unit 252 determines that there is an abnormality if the following conditions are met.
Condition: Maximum value of the second harmonic (2fa0, 2fb0, 2fc0) > fourth threshold. The frequency determination unit 252 uses at least one of these determination results, as explained with reference to Figure 2.

(Step S9) The frequency determination unit 252 stores the following information in the storage unit 26: the operation date and time information, the primary current interruption determination result and three-phase current value (before and during the switching operation), the load-side voltage interruption determination result and three-phase voltage value (before and during the switching operation), the sound level determination result and detected value (before and after the switching operation), and the second harmonic detection determination result and detected value (during the switching operation).

(Step S10) The frequency determination unit 252 reads from the storage unit 26 the most recent N data entries for the operation date and time, the primary current interruption judgment result and three-phase current value (before and during switching operation), the load-side voltage interruption judgment result and three-phase voltage value (before and during switching operation), the sound level judgment result and detected value (before and after switching operation), and the second harmonic detection judgment result and detected value (during switching operation).

(Step S11) The frequency determination unit 252 analyzes the read data to determine the detection count M (where M is the set number of detections).

(Step S12) The frequency determination unit 252 determines whether or not detection operations occurred M (fifth threshold) or more times in the most recent N times. If the frequency determination unit 252 determines that detection operations occurred M or more times in the most recent N times (Step S12; YES), the process proceeds to Step S13. If the frequency determination unit 252 determines that detection operations did not occur M or more times in the most recent N times (Step S12; NO), the process returns to Step S1.

(Step S13) The frequency determination unit 252 notifies an abnormality by, for example, displaying an operation alarm or outputting an operation warning to an external device.

(Step S14) The frequency determination unit 252 outputs an operation lock signal for the tap changer.

(Step S15) The frequency determination unit 252 receives the corresponding command. After processing, the frequency determination unit 252 returns to the processing of step S1.

Furthermore, the processing flow also includes other processing functions in separate routines, such as recording data retrieval, setting value configuration, external operation information output processing, and watchdog functionality.

[Verification Results]
Next, an example of the verification results will be explained with reference to Figure 2.
Here, instantaneous voltage drop detection has been successfully implemented in numerous applications using protective relays, etc. Second harmonic detection has been successfully implemented in numerous applications using protective relays, etc. Current detection has been successfully implemented in numerous applications using protective relays, etc. Command value detection can be achieved with general-purpose auxiliary relays. Sound level detection can be achieved, for example, by sound collectors or vibration sensors, etc. Motor drive detection can be achieved, for example, by motor current or motor voltage detection circuits (non-contact detection).

Figure 10 shows an example of the external appearance of a wire break detection device according to this embodiment. In the example in Figure 10, for example, the wire break detection device 2 includes a display unit 27, an operation unit 28, and an operation information output unit 24. The wire break detection device 2 receives detection results from each detection unit and is supplied with the power necessary for the operation of each unit (110). The operation information output unit 24 is, for example, an LED (light-emitting diode). If an abnormality is detected, the operation information output unit 24 lights up to notify the abnormality. Such a wire break detection device 2 can be installed, for example, near power equipment having a transformer, to detect abnormalities such as wire breaks or bridging in current-reducing resistors connected to the transformer.

It should be noted that the wire break detection device 2 does not need to have all detection units connected to it; it may have just one of the first detection units 110 (voltage detection unit 14, acoustic detection unit 15, content detection unit 16, current detection unit 17), or it may have just one of the second detection units 120 (motor current voltage detection unit 18, command detection unit 22).
For example, even when the wire break detection device 2 consists of an acoustic detection unit 15 and a motor current voltage detection unit 18, verification showed that it was possible to detect an abnormality.

[Application Examples]
The following describes an example of an application of the embodiment described above.
(1) Advanced functionality of transformer protection relays Power transformers are generally equipped with ratio-actuated relays for detecting internal faults, and digital relays are now the mainstream.
Ratio-actuated relays take in the primary and secondary currents of the transformer, and because a second harmonic suppression method is generally used to prevent malfunctions caused by the inrush current when the transformer is switched on, they are equipped with a second harmonic detection circuit.
In this ratio-operated relay, by adding a primary current interruption determination element using transformer primary current information, reusing the existing second harmonic detection element, and incorporating load-operated tap changer operation information, the current-reducing resistor disconnection detection function of the aforementioned disconnection detection device 2 can be easily configured and added as an additional function.

(2) Acquisition of transformer maintenance information The transformer primary current element and on-load tap changer operation information, which are taken into the break detection device 2 of this embodiment and used, can be utilized as maintenance information for the on-load tap changer by adding operation time information in the break detection device 2.
In other words, by using switching current information and operation count information as an additional function of the wire break detection device 2, or by transmitting the information to the host and managing the responsibilities of the tap changer, it can be used to set the optimal inspection timing for the tap changer and its auxiliary equipment (live-line oil purifier, etc.) under load, and to determine when to replace the equipment.

Furthermore, a program to implement all or part of the functions of the wire break detection device 2 in this invention may be recorded on a computer-readable recording medium, and all or part of the processing performed by the wire break detection device 2 may be performed by loading the program recorded on this recording medium into a computer system and executing it. Here, "computer system" includes hardware such as the OS and peripheral devices. "Computer system" also includes a WWW system equipped with a homepage provisioning environment (or display environment). "Computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, and storage devices such as hard disks built into computer systems. Furthermore, "computer-readable recording medium" also includes volatile memory (RAM) within a computer system that acts as a server or client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line, which retains the program for a certain period of time.

Furthermore, the above program may be transmitted from a computer system storing this program in a memory device or the like to another computer system via a transmission medium, or by transmission waves within the transmission medium. Here, the "transmission medium" for transmitting the program refers to a medium that has the function of transmitting information, such as a network (communication network) like the Internet or a communication line (communication line) like a telephone line. Also, the above program may be intended to implement only a part of the aforementioned functions. Furthermore, it may be a program that can implement the aforementioned functions in combination with a program already recorded in the computer system, a so-called differential file (differential program).

Although embodiments for carrying out the present invention have been described above using examples, the present invention is not limited in any way to these embodiments, and various modifications and substitutions can be made without departing from the spirit of the invention.

1...Disconnection detection system, 2...Disconnection detection device, 11...Power supply busbar, 12...Load tap changer transformer, 13...Load side busbar, 14...Voltage detection unit, 15...Acoustic detection unit, 16...Concentration detection unit, 17...Current detection unit, 18...Motor current voltage detection unit, 19...Tap changer electric operation mechanism, 20...Drive motor, 21...Motor power supply, 22...Command detection unit, 23...Detection processing unit, 24...Operation information 25...Information output unit, 26...Processing unit, 27...Storage unit, 28...Operation unit, 100...Detection unit, 110...First detection unit, 120...Second detection unit, 121...Primary current transformer, 231...Concentration determination unit, 232...Current interruption detection unit, 233...Instantaneous voltage drop detection unit, 234...Acoustic increase detection unit, 235...One-shot circuit, 236...OR circuit, 251...OR circuit, 252...Frequency determination unit

Claims (8)

A first detection unit that detects at least one of the following: the primary current of the transformer, the second harmonic component of the primary current of the transformer, the secondary voltage of the transformer, and an acoustic signal near the transformer body.
A second detection unit that detects at least one of a switching command for a tap changer and the current or voltage flowing to a motor for switching the tap changer,
A detection processing unit compares the first detection result detected by the first detection unit with a threshold value to make a determination or detection, and outputs a tap switching operation signal based on the second detection result detected by the second detection unit.
A processing unit that determines and displays whether the current reducing resistor built into the tap changer and connected to the transformer is normal or abnormal, based on the determination or detected result output by the detection processing unit and the tap switching operation signal,
Equipped with ,
The detection processing unit calculates the moving average value of the primary current before the tap switching operation of the tap changer, and calculates the minimum value of the primary current during the tap switching operation.
The processing unit determines that a momentary interruption has occurred in the primary current when the moving average value of the primary current is greater than the load current detection level and the minimum value of the primary current is less than the first threshold, and issues an abnormality notification indicating that the current reducing resistor is abnormal.
Wire break detection device. A first detection unit that detects at least one of the following: the primary current of the transformer, the second harmonic component of the primary current of the transformer, the secondary voltage of the transformer, and an acoustic signal near the transformer body.
A second detection unit that detects at least one of a switching command for a tap changer and the current or voltage flowing to a motor for switching the tap changer,
A detection processing unit compares the first detection result detected by the first detection unit with a threshold value to make a determination or detection, and outputs a tap switching operation signal based on the second detection result detected by the second detection unit.
A processing unit that determines and displays whether the current reducing resistor built into the tap changer and connected to the transformer is normal or abnormal, based on the determination or detected result output by the detection processing unit and the tap switching operation signal,
Equipped with,
The detection processing unit calculates the moving average value of the secondary voltage before the tap switching operation of the tap changer, and calculates the minimum value of the secondary voltage during the tap switching operation.
The processing unit determines that the secondary voltage is momentarily interrupted when the difference between the moving average value of the secondary voltage and the minimum value of the secondary voltage is greater than the second threshold, and issues an abnormality notification indicating that the current reducing resistor is abnormal.
Wire break detection device. A first detection unit that detects at least one of the following: the primary current of the transformer, the second harmonic component of the primary current of the transformer, the secondary voltage of the transformer, and an acoustic signal near the transformer body.
A second detection unit that detects at least one of a switching command for a tap changer and the current or voltage flowing to a motor for switching the tap changer,
A detection processing unit compares the first detection result detected by the first detection unit with a threshold value to make a determination or detection, and outputs a tap switching operation signal based on the second detection result detected by the second detection unit.
A processing unit that determines and displays whether the current reducing resistor built into the tap changer and connected to the transformer is normal or abnormal, based on the determination or detected result output by the detection processing unit and the tap switching operation signal,
Equipped with,
The detection processing unit calculates a moving average of the magnitude of the acoustic signal before the tap switching operation of the tap switcher, and detects the magnitude of the acoustic signal after the tap switching operation.
The processing unit determines that there is an acoustic abnormality when the difference between the magnitude of the acoustic signal after the tap switching operation and the moving average value of the magnitude of the acoustic signal before the tap switching operation is greater than a third threshold, and issues an abnormality notification indicating that the current reducing resistor is abnormal.
Wire break detection device. A first detection unit that detects at least one of the following: the primary current of the transformer, the second harmonic component of the primary current of the transformer, the secondary voltage of the transformer, and an acoustic signal near the transformer body.
A second detection unit that detects at least one of a switching command for a tap changer and the current or voltage flowing to a motor for switching the tap changer,
A detection processing unit compares the first detection result detected by the first detection unit with a threshold value to make a determination or detection, and outputs a tap switching operation signal based on the second detection result detected by the second detection unit.
A processing unit that determines and displays whether the current reducing resistor built into the tap changer and connected to the transformer is normal or abnormal, based on the determination or detected result output by the detection processing unit and the tap switching operation signal,
Equipped with,
The detection processing unit calculates the maximum value of the second harmonic of the primary current,
The processing unit determines that the second harmonic is abnormal if the maximum value of the second harmonic is greater than the fourth threshold during or after the tap switching operation of the tap switcher, and issues an abnormality notification indicating that the current reducing resistor is abnormal.
Wire break detection device. The processing unit counts the number of occurrences of the determined determination result a predetermined number of times, and if the count value is equal to or greater than the fifth threshold, it determines that the current reducing resistor is abnormal and issues a notification.
A wire break detection device according to any one of claims 1 to 4 . The detection processing unit acquires the switching command output by the second detection unit for a period equivalent to the switching time.
A wire break detection device according to any one of claims 1 to 4 . The first detection unit detects at least one of the following: the primary current of the transformer, the second harmonic component of the primary current of the transformer, the secondary voltage of the transformer, and an acoustic signal near the transformer body.
The second detection unit detects at least one of the following: a switching command for the tap changer, and the current or voltage flowing to the motor for switching the tap changer.
The detection processing unit compares the first detection result detected by the first detection unit with a threshold value to make a determination or detection, and outputs a tap switching operation signal based on the second detection result detected by the second detection unit.
A wire break detection method comprising: a processing unit determining and displaying whether a current reducing resistor built into the tap changer and connected to the transformer is normal or abnormal, based on the determination or detection result output by the detection processing unit and the tap switching operation signal;
The detection processing unit calculates the moving average value of the primary current before the tap switching operation of the tap changer, and calculates the minimum value of the primary current during the tap switching operation.
The processing unit determines that a momentary interruption has occurred in the primary current when the moving average value of the primary current is greater than the load current detection level and the minimum value of the primary current is less than the first threshold, and issues an abnormality notification indicating that the current reducing resistor is abnormal.
Method for detecting wire breakage. On the computer,
The system detects at least one of the following as a first detection result: the primary current of the transformer, the second harmonic component of the primary current of the transformer, the secondary voltage of the transformer, and an acoustic signal near the transformer body.
The system detects at least one of the following as a second detection result: a switching command for the tap changer, and the current or voltage flowing to the motor for switching the tap changer.
The first detection result is compared with a threshold value to make a determination or detection, and a tap switching operation signal is output based on the second detection result.
A program that determines and displays whether the current reducing resistor built into the tap changer and connected to the transformer is normal or abnormal, based on the first detection result and the threshold value, and the tap switching operation signal,
The moving average value of the primary current before the tap switching operation of the tap changer is calculated, and the minimum value of the primary current during the tap switching operation is calculated.
If the moving average value of the primary current is greater than the load current detection level and the minimum value of the primary current is less than the first threshold, it is determined that a momentary interruption has occurred in the primary current, and an abnormality notification is issued indicating that the current reducing resistor is abnormal.
program.