Power distribution transformer high-voltage side disconnection fault positioning method and system

Abstract

The application provides a power distribution transformer high-voltage side disconnection fault positioning method and system, and belongs to the technical field of power distribution. The method comprises the following steps: obtaining a disconnection detection enabling identifier; if the disconnection detection enabling identifier is in an enabling state, performing the steps of transformer high-voltage side disconnection fault positioning detection: obtaining high-voltage side monitoring data and low-voltage side monitoring data of the transformer at multiple time points; determining the amplitude of high-voltage side three-phase voltage, the amplitude of high-voltage side three-phase current and the state monitoring result of the drop-out fuse based on the high-voltage side monitoring data and the low-voltage side monitoring data at the multiple time points; determining the amplitude and phase of low-voltage side three-phase voltage and the amplitude of low-voltage side three-phase current based on the low-voltage side monitoring data at the multiple time points; if the drop-out fuse is in a closed state and the first preset condition is met, positioning the disconnection fault of the transformer high-voltage side based on the amplitude and phase of low-voltage side three-phase voltage. The application can improve the operation and maintenance efficiency of the power distribution network.

Description

Technical Field

[0001] This application belongs to the field of power distribution technology, and more specifically, relates to a method and system for locating faults on the high-voltage side of a power distribution transformer. Background Technology

[0002] Transformers are key equipment in the operation of power distribution networks. A break in the high-voltage side of a transformer (i.e., a break in the line between the distribution line's disconnection point and the transformer's high-voltage terminal) will cause a severe imbalance in the three-phase voltage on the low-voltage side, burning out downstream electrical equipment. At the same time, a break in the high-voltage side of a transformer will cause abnormal magnetic flux, increased vibration and temperature rise, and long-term operation will cause damage to the winding insulation and burnout of the transformer itself.

[0003] When the high-voltage side of a transformer is disconnected, the electromagnetic coupling is broken, and the electrical characteristics of the low-voltage side are distorted. For example, the voltage amplitude of the fault phase drops, and the three-phase voltage phases deviate from the standard 120° arrangement. Moreover, the voltage drop amplitude and phase shift on the low-voltage side differ depending on the phase and location of the disconnection. Based on this, a detection method for high-voltage side disconnection fault identification based on the electrical characteristics of the low-voltage side of the transformer has been proposed in related research. This method poses no risk of high-voltage electric shock and is simple to install and maintain.

[0004] In practical use, it has been found that the method of judging high-voltage side open circuit faults based on the electrical characteristics of the low-voltage side of the transformer has the problem of false alarms, which affects the operation and maintenance efficiency of the distribution network. Summary of the Invention

[0005] The purpose of this application is to provide a method and system for locating faults on the high-voltage side of a distribution transformer, so as to solve the technical problem of false alarms in the existing methods for judging faults on the high-voltage side of a transformer, and improve the operation and maintenance efficiency of the distribution network.

[0006] A first aspect of this application provides a method for locating a high-voltage side open-circuit fault in a distribution transformer, comprising: Obtain the disconnection detection enable flag; If the disconnection detection enable flag is enabled, then high-voltage side monitoring data and low-voltage side monitoring data of the transformer at multiple times are acquired; the multiple times include the current time and multiple times within the first monitoring period before the current time; the high-voltage side monitoring data includes the high-voltage side three-phase instantaneous voltage, the high-voltage side three-phase instantaneous current and the on / off state of the drop-out fuse; the low-voltage side monitoring data includes the low-voltage side three-phase instantaneous voltage and the low-voltage side three-phase instantaneous current. The amplitude of the three-phase voltage on the high-voltage side is determined based on the instantaneous three-phase voltage on the high-voltage side at multiple times; the amplitude of the three-phase current on the high-voltage side is determined based on the instantaneous three-phase current on the high-voltage side at multiple times; and the status monitoring results of the drop-out fuse are determined based on the closing / opening status of the drop-out fuse at multiple times. The amplitude and phase of the three-phase voltage on the low-voltage side are determined based on the instantaneous three-phase voltage on the low-voltage side at multiple moments, and the amplitude of the three-phase current on the low-voltage side is determined based on the instantaneous three-phase current on the low-voltage side at multiple moments. If the status monitoring result of the drop-out fuse shows that the drop-out fuse is in the closed state and meets the first preset condition, then the fault location of the high-voltage side of the transformer is performed based on the amplitude and phase of the three-phase voltage on the low-voltage side. Wherein, if the amplitude of the three-phase current on the high-voltage side is greater than a preset current threshold, the first preset condition includes: the amplitude of the three-phase voltage on the high-voltage side is greater than a preset voltage threshold, and the error between the amplitude of the converted current of each phase and the amplitude of the low-voltage side current of the corresponding phase is within a preset error range; the amplitude of the converted current of each phase is obtained by converting the amplitude of the high-voltage side current of the corresponding phase to the low-voltage side based on a preset current ratio.

[0007] A second aspect of this application provides a fault location system for a high-voltage side open circuit of a distribution transformer, comprising: A drop-out fuse monitoring unit is installed on the high-voltage side of the transformer and is configured to collect high-voltage side monitoring data of the transformer at multiple times. The multiple times include the current time and multiple times within a first monitoring period before the current time. The high-voltage side monitoring data includes the high-voltage side three-phase instantaneous voltage, the high-voltage side three-phase instantaneous current, and the on / off status of the drop-out fuse. The terminal equipment, located on the low-voltage side of the transformer, is configured to collect low-voltage side monitoring data of the transformer at multiple times; the low-voltage side monitoring data includes the three-phase instantaneous voltage and the three-phase instantaneous current on the low-voltage side. The controller is communicatively connected to the drop-out fuse monitoring unit and the terminal device, respectively, and is configured to perform the steps of the above-described method for locating faults on the high-voltage side of the distribution transformer.

[0008] The beneficial effects of the high-voltage side open-circuit fault location method and system for distribution transformers provided in this application are as follows: This embodiment addresses a major reason for false alarms caused by high-voltage side open-circuit faults in transformers: when a high-voltage side open-circuit fault occurs, the electrical characteristics of the low-voltage side are similar to those corresponding to low-voltage side short-circuit faults and low-voltage side single-phase ground faults. Therefore, low-voltage side short-circuit faults and low-voltage side single-phase ground faults can cause false triggering of high-voltage side open-circuit faults. To avoid this problem, this embodiment sets an open-circuit detection enable flag. During transformer operation, the open-circuit detection enable flag is continuously updated based on the specific circumstances of low-voltage side short-circuit faults and low-voltage side single-phase ground faults. The high-voltage side open-circuit fault location detection step is only executed when the open-circuit detection enable flag is enabled, thereby preventing false triggering of high-voltage side open-circuit faults caused by low-voltage side short-circuit faults and low-voltage side single-phase ground faults.

[0009] Furthermore, in the step of performing high-voltage side open circuit fault location detection in the embodiments of this application, it is first determined whether the drop-out fuse is in the closed position and whether there is any winding or disconnection inside the transformer. When it is ensured that the drop-out fuse is in the closed position and there is no winding or disconnection inside the transformer, the high-voltage side open circuit fault location detection is then performed, which can further avoid the false triggering of high-voltage side open circuit faults.

[0010] Therefore, this application embodiment uses a dual verification mechanism of disconnection detection enable flag and preconditions to eliminate interference factors such as low-voltage side short-circuit faults, low-voltage side single-phase grounding faults, the status of drop-out fuses, and transformer body disconnection, which can effectively avoid false triggering of high-voltage side disconnection faults and improve the operation and maintenance efficiency of the distribution network. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 A flowchart illustrating a method for locating a high-voltage side open circuit fault in a distribution transformer, as provided in an embodiment of this application. Figure 2 A schematic diagram of the power supply circuit of a drop-out fuse monitoring unit provided in an embodiment of this application. Detailed Implementation

[0013] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0014] To make the objectives, technical solutions, and advantages of this application clearer, the following description will be provided in conjunction with the accompanying drawings and specific embodiments.

[0015] Please refer to Figure 1 , Figure 1 This is a flowchart illustrating a method for locating a high-voltage side open-circuit fault in a distribution transformer according to an embodiment of this application. The method can be executed by a controller and includes: S101: Obtain the disconnection detection enable flag.

[0016] In this embodiment, considering that when a high-voltage side open circuit fault occurs, the electrical characteristics of the low-voltage side are similar to those of a low-voltage side short circuit fault and a low-voltage side single-phase ground fault, for example, both will cause abnormal amplitude / phase of the three-phase voltage on the low-voltage side. Therefore, in order to avoid the low-voltage side short circuit fault and low-voltage side single-phase ground fault being misjudged as a high-voltage side open circuit fault, this embodiment sets an open circuit detection enable flag. The open circuit detection enable flag adopts a binary assignment form and is continuously updated during the operation of the transformer. For example, 1 indicates the enabled state and 0 indicates the disabled state.

[0017] Specifically, when a short circuit or single-phase grounding fault is detected on the low-voltage side of the transformer, the open circuit detection enable flag is set to the disabled state, blocking the open circuit fault detection process; after the low-voltage side short circuit fault or low-voltage side single-phase grounding fault is eliminated, the open circuit detection enable flag is restored to the enabled state, and the open circuit fault detection process is restarted.

[0018] S102: If the disconnection detection enable flag is enabled, then acquire the high-voltage side monitoring data and low-voltage side monitoring data of the transformer at multiple times; multiple times include the current time and multiple times within the first monitoring duration before the current time. The high-voltage side monitoring data includes the high-voltage side three-phase instantaneous voltage, the high-voltage side three-phase instantaneous current and the on / off state of the drop-out fuse. The low-voltage side monitoring data includes the low-voltage side three-phase instantaneous voltage and the low-voltage side three-phase instantaneous current.

[0019] In this embodiment, a drop-out fuse is typically installed between the power distribution line's disconnection point and the transformer's high-voltage terminal to provide overload and short-circuit protection for the transformer, creating a clear break point for convenient power outage maintenance. Correspondingly, a drop-out fuse monitoring unit is configured on the high-voltage side of the transformer to collect the open / closed state of the drop-out fuse according to a preset acquisition cycle (e.g., 1 second). Furthermore, the drop-out fuse monitoring unit can also monitor the instantaneous three-phase voltage and current on the high-voltage side. The drop-out fuse is a three-phase fuse. At any given moment, if all three phase fuses are in the closed state, the drop-out fuse's open / closed state is determined to be closed; otherwise, if even one phase fuse is in the open state, the drop-out fuse's open / closed state is determined to be open.

[0020] Meanwhile, a distribution terminal is installed on the low-voltage side of the transformer. Based on the distribution terminal, the three-phase instantaneous voltage and current of the low-voltage side can be collected according to a preset acquisition cycle. The acquisition cycle of the distribution terminal and the acquisition cycle of the drop-out fuse monitoring unit are synchronized to achieve time alignment of the high-voltage side monitoring data and the low-voltage side monitoring data.

[0021] S103: Determine the amplitude of the three-phase voltage on the high-voltage side based on the instantaneous three-phase voltage on the high-voltage side at multiple times; determine the amplitude of the three-phase current on the high-voltage side based on the instantaneous three-phase current on the high-voltage side at multiple times; and determine the status monitoring result of the drop-out fuse based on the closing / opening status of the drop-out fuse at multiple times.

[0022] In this embodiment, multiple moments need to cover at least one complete power frequency cycle. The instantaneous three-phase voltage on the high-voltage side is the instantaneous value of the three-phase voltage on the high-voltage side. By performing root mean square calculation on the instantaneous values ​​of each phase voltage on the high-voltage side at multiple moments, the effective value of that phase voltage can be obtained. Multiplying the effective value by... The amplitude of the phase voltage can be obtained; similarly, the instantaneous current of the three phases on the high-voltage side is also the instantaneous value of the three-phase current on the high-voltage side. By performing root mean square calculation on the instantaneous values ​​of each phase current on the high-voltage side at multiple times, the effective value of the phase current can be obtained. Multiplying the effective value by... The amplitude of the phase current can be obtained.

[0023] Furthermore, the condition monitoring results of the drop-out fuse can be determined based on the closed / open state of the drop-out fuse at multiple times, specifically including: Select the most recent N times from the closed / open states of the drop-out fuse at multiple times; If the closed / open state of the drop-out fuse is closed for the most recent N times, then the state monitoring result of the drop-out fuse is determined to be closed. Otherwise, the status monitoring result of the drop-out fuse is determined to be in the vacancy state.

[0024] In this embodiment, considering that the status data at a single moment may contain momentary false alarms, the status data of the most recent N moments (e.g., 5 moments) are selected as the basis for judgment to determine the status monitoring result of the drop-out fuse. Specifically, the status monitoring result of the drop-out fuse is determined to be in the closed state only if the closed / open state of the drop-out fuse is closed for the most recent N moments; otherwise, the status monitoring result of the drop-out fuse is determined to be in the open state as long as the closed / open state of the drop-out fuse is open at any moment.

[0025] S104: Determine the amplitude and phase of the three-phase voltage on the low-voltage side based on the three-phase instantaneous voltage at multiple moments, and determine the amplitude of the three-phase current on the low-voltage side based on the three-phase instantaneous current at multiple moments.

[0026] In this embodiment, the instantaneous voltage of the three phases on the low-voltage side, that is, the instantaneous value of the three phase voltage on the low-voltage side, can be obtained by performing a discrete Fourier transform on the instantaneous value of each phase voltage on the low-voltage side at multiple moments within a power frequency cycle, extracting the power frequency fundamental component, and obtaining the amplitude and phase of the fundamental wave as the amplitude and phase of the phase voltage.

[0027] Meanwhile, the instantaneous three-phase current on the low-voltage side, which is also the instantaneous value of the three-phase current on the low-voltage side, can be obtained by performing root mean square calculation on the instantaneous values ​​of each phase current at multiple times. The effective value of that phase current can then be multiplied by... The amplitude of the phase current can be obtained.

[0028] S105: If the status monitoring result of the drop-out fuse shows that the drop-out fuse is in the closed position and meets the first preset condition, then the fault location of the high-voltage side of the transformer is performed based on the amplitude and phase of the three-phase voltage on the low-voltage side.

[0029] If the amplitude of the three-phase current on the high-voltage side is greater than the preset current threshold, the first preset condition includes: the amplitude of the three-phase voltage on the high-voltage side is greater than the preset voltage threshold, and the error between the amplitude of the converted current of each phase and the amplitude of the low-voltage side current of the corresponding phase is within the preset error range; the amplitude of the converted current of each phase is obtained by converting the amplitude of the high-voltage side current of the corresponding phase to the low-voltage side based on the preset current ratio.

[0030] In this embodiment, considering that a break in the high-voltage side of the transformer will cause voltage and phase distortion on the low-voltage side, and that the voltage drop and phase shift on the low-voltage side are different for different phases and locations of the break, the fault location of the break in the high-voltage side of the transformer can be determined based on the amplitude and phase of the three-phase voltage on the low-voltage side.

[0031] Furthermore, considering that when a drop-out fuse is in the open position, it creates a break between the power distribution line's disconnection point and the transformer's high-voltage terminal, causing voltage and phase distortion on the low-voltage side; and that the transformer contains windings and connectors, if these windings or connectors break, it will also cause voltage and phase distortion on the low-voltage side, both of these situations could lead to misdiagnosis of a high-voltage side open circuit fault.

[0032] To avoid the above problems, this embodiment first determines whether the drop-out fuse is in the closed position and whether there are any windings or joints inside the transformer that are disconnected before locating the open circuit fault on the high-voltage side of the transformer based on the amplitude and phase of the three-phase voltage on the low-voltage side. Only when it is ensured that the drop-out fuse is in the closed position and that there are no windings or joints disconnected inside the transformer can the open circuit fault on the high-voltage side be located.

[0033] Specifically, when determining whether a drop-out fuse is in the closed position, the status monitoring results of the drop-out fuse obtained in the above steps can be used to determine this. When determining whether there is a winding or joint disconnection inside the transformer, the load condition of the transformer can be determined first based on the magnitude of the three-phase current on the high-voltage side. There are different judgment methods for the two different load conditions of on-load and no-load.

[0034] For example, a current threshold can be preset (e.g., 1.5 times the rated no-load current). If the amplitude of the three-phase current on the high-voltage side is greater than the current threshold, it indicates that the transformer is in a loaded condition. Under the loaded condition, the conditions that need to be met (i.e., the first preset condition) are: the amplitude of the three-phase voltage on the high-voltage side is greater than the preset voltage threshold (e.g., 85% of the rated phase voltage on the high-voltage side), and after converting the amplitude of the three-phase current on the high-voltage side to the low-voltage side, the amplitude of the converted current of each phase is equal to the amplitude of the corresponding phase's low-voltage side current, that is, the error between the two is within a preset error range (e.g., ±5% of the amplitude of the low-voltage side current).

[0035] If the amplitude of the three-phase current on the high-voltage side is less than or equal to the current threshold, it indicates that the transformer is in no-load condition. Under no-load condition, the conditions that need to be met (i.e. the first preset condition) are: the amplitude of the three-phase voltage on the high-voltage side is greater than the preset voltage threshold, and the three-phase voltage on the low-voltage side is balanced, that is, the amplitude of the three-phase voltage on the low-voltage side is equal and the phase difference is 120°.

[0036] As can be seen from the above, this embodiment considers a major reason for false alarms caused by high-voltage side open circuit faults in transformers: when a high-voltage side open circuit fault occurs, the electrical characteristics of the low-voltage side are similar to those corresponding to low-voltage side short circuit faults and low-voltage side single-phase ground faults. Therefore, low-voltage side short circuit faults and low-voltage side single-phase ground faults are mistakenly identified as high-voltage side open circuit faults, resulting in false triggering of high-voltage side open circuit faults. To avoid the above problem, this embodiment sets an open circuit detection enable flag, and during transformer operation, the open circuit detection enable flag is continuously updated according to the specific circumstances of low-voltage side short circuit faults and low-voltage side single-phase ground faults. The high-voltage side open circuit fault location detection step is only executed when the open circuit detection enable flag is enabled, thereby avoiding false triggering of high-voltage side open circuit faults caused by low-voltage side short circuit faults and low-voltage side single-phase ground faults.

[0037] Furthermore, in the step of performing the fault location detection of the high-voltage side of the transformer, this embodiment first determines whether the drop-out fuse is in the closed position and whether there is a winding or joint disconnection inside the transformer. Only when it is ensured that the drop-out fuse is in the closed position and there is no winding or joint disconnection inside the transformer is the fault location detection of the high-voltage side is performed, which can further avoid the false triggering of the high-voltage side fault.

[0038] Therefore, this embodiment uses a dual verification mechanism of disconnection detection enable flag and preconditions to eliminate interference factors such as low-voltage side short-circuit faults, low-voltage side single-phase grounding faults, the status of drop-out fuses, and transformer body disconnection, which can effectively avoid false triggering of high-voltage side disconnection faults and improve the operation and maintenance efficiency of the distribution network.

[0039] In one embodiment of this application, when locating a broken wire fault on the high-voltage side of a transformer based on the amplitude and phase of the three-phase voltage on the low-voltage side, the following steps can be taken: The amplitude coefficient of each phase voltage is calculated based on the amplitude of each phase voltage and the preset rated voltage amplitude. Calculate the phase difference between each pair of adjacent phase voltages to obtain three phase differences between phases; Based on the amplitude coefficient of each phase voltage and the phase difference between the three phases, a preset feature library is searched to obtain the fault location information of the high-voltage side of the transformer. The preset feature library includes the correspondence between the amplitude coefficient of each phase voltage, the phase difference between the three phases and the fault location results. The fault location information includes the phase of the fault and the location of the fault. The location result of the open circuit fault on the high-voltage side of the transformer is determined based on the open circuit fault location information.

[0040] In this embodiment, the inventors have conducted extensive experimental research and found that each combination of the phase and location of the broken wire corresponds to a specific low-voltage side electrical characteristic, namely, the amplitude and phase relationship of the three-phase voltage on the low-voltage side. Therefore, a correspondence between the amplitude and phase relationship of the three-phase voltage on the low-voltage side and the fault location information (including the phase and location of the broken wire) can be pre-constructed based on historical fault data. On this basis, the fault location information can be obtained by finding the above correspondence based on the amplitude and phase of the three-phase voltage on the low-voltage side that are actually detected.

[0041] Specifically, historical fault data includes historical amplitude data of the three-phase voltage on the low-voltage side corresponding to different historical open circuit fault location information, as well as historical phase data of the three-phase voltage on the low-voltage side. When constructing the correspondence between the amplitude and phase relationship of the three-phase voltage on the low-voltage side and the open circuit fault location information (including the open circuit phase and the open circuit location) based on historical fault data, the ratio between the historical amplitude data of each phase voltage and the preset rated voltage amplitude (e.g., 311V) can be calculated first as the historical amplitude coefficient of each phase voltage. The historical amplitude coefficient of each phase voltage can be used to intuitively represent the historical amplitude of the three-phase voltage on the low-voltage side. Simultaneously, the difference between the historical phase data of each adjacent pair of phase voltages is calculated as the historical phase difference between each adjacent pair of phase voltages. Assuming the three-phase voltages on the low-voltage side are A / B / C, the historical phase differences between each adjacent pair of phase voltages are respectively the historical phase differences between phases AB, BC, and CA. The historical phase differences between each adjacent pair of phase voltages can intuitively represent the historical phase relationship of the three-phase voltages on the low-voltage side. Finally, the correspondence between the historical amplitude coefficient of each phase voltage, the historical phase differences between the three phases, and the historical open circuit fault location information is saved to the feature library. Table 1 below shows a specific example of the feature library: Table 1 - Example of Feature Library

[0042] In Table 1 above, an upstream disconnection refers to a fault point located near the downstream end of the distribution line, while a downstream disconnection refers to a fault point located near the high-voltage terminal of the transformer. When the faulty phase (e.g., phase A) experiences an upstream disconnection, the power supply for that phase cannot be connected to the high-voltage winding via the line. The high-voltage winding of that phase has almost no grid induced electromotive force, and only residual voltage is induced by the weak coupling of the magnetic fields of the other two phases. The voltage drop of the corresponding phase on the low-voltage side is deep, the voltage amplitude coefficient is small, and the three-phase phase distortion amplitude is large. When the faulty phase (e.g., phase B) experiences a downstream disconnection, the high-voltage incoming line is energized, the break point is at the front end of the winding, and the conductor near the line side of the break point has a power frequency floating potential, which is coupled to the winding through stray capacitance. The residual induced voltage of the corresponding phase on the low-voltage side is high, the voltage amplitude coefficient is large, and the three-phase phase offset amplitude is small.

[0043] Based on the feature library, the amplitude of each phase voltage is divided by the preset rated voltage amplitude to obtain the amplitude coefficient of each phase voltage. At the same time, the phase difference between each pair of adjacent phase voltages is calculated to obtain the three phase differences between phases. Finally, based on the amplitude coefficient of each phase voltage and the three phase differences between phases, the feature library is searched to obtain the fault location information of the high-voltage side of the transformer. Thus, the fault location result of the high-voltage side of the transformer is determined based on the fault location information.

[0044] In one embodiment of this application, the step of determining the location result of a broken wire fault on the high-voltage side of a transformer based on the broken wire fault location information includes: If the fault location information indicates that there is a fault on the high-voltage side of the transformer, then obtain the current amplitude of the faulty phase and the zero-sequence current on the low-voltage side. If the current amplitude of the disconnected phase is greater than the preset short-circuit current threshold, or the zero-sequence current on the low-voltage side is greater than the preset zero-sequence current threshold, then the fault location result on the high-voltage side of the transformer is determined to be no fault, and the fault detection enable flag is set to the disabled state. Otherwise, the fault location information will be determined as the fault location result on the high-voltage side of the transformer.

[0045] In this embodiment, if the fault location information indicates that there is a fault on the high-voltage side of the transformer, it is necessary to further verify whether the fault is a misjudgment caused by a short circuit fault on the low-voltage side or a single-phase grounding fault on the low-voltage side.

[0046] Specifically, when the high-voltage side is disconnected, the primary circuit is open, the current in the faulted phase is relatively small, and there is no significant zero-sequence current on the low-voltage side of the transformer. However, a short-circuit fault on the low-voltage side is accompanied by a surge in the current in the faulted phase, and a single-phase ground fault on the low-voltage side is accompanied by an excessive zero-sequence current. Therefore, when the fault location information indicates a fault on the high-voltage side of the transformer, it can be further verified by checking the current in the faulted phase and the zero-sequence current on the low-voltage side.

[0047] For example, if the current amplitude of the faulty phase is greater than a preset short-circuit current threshold (e.g., 6 times the rated phase current of the low voltage), it indicates that the distortion of the voltage amplitude and phase on the low voltage side is caused by a short-circuit fault on the low voltage side; if the zero-sequence current on the low voltage side is greater than a preset zero-sequence current threshold (e.g., 10% of the rated phase current of the low voltage), it indicates that the distortion of the voltage amplitude and phase on the low voltage side is caused by a ground fault on the low voltage side; both of the above situations indicate that the high-voltage side open circuit fault is misjudged. At this time, it can be determined that the open circuit fault location result on the high-voltage side of the transformer is no open circuit fault, and the open circuit detection enable flag is set to the disabled state, and the step of high-voltage side open circuit fault location detection is no longer performed.

[0048] Otherwise, if the current amplitude of the disconnected phase is less than or equal to the preset short-circuit current threshold, and the zero-sequence current on the low-voltage side is less than or equal to the preset zero-sequence current threshold, it indicates that there is a real high-voltage side disconnection fault, and the disconnection fault location information will be output as the result of the high-voltage side disconnection fault location of the transformer.

[0049] In one embodiment of this application, after the disconnection detection enable flag is set to the disabled state, if the amplitude of the three-phase current on the low-voltage side and the zero-sequence current on the low-voltage side meet the second preset condition within a preset second monitoring period (e.g., 5 minutes), it indicates that the low-voltage side short-circuit fault and the low-voltage side ground fault have been eliminated. At this time, the disconnection detection enable flag can be set to the enabled state.

[0050] The second preset condition is that the amplitude of the three-phase current on the low-voltage side is less than or equal to the preset short-circuit current threshold, and the zero-sequence current on the low-voltage side is less than or equal to the preset zero-sequence current threshold.

[0051] Corresponding to the high-voltage side open circuit fault location method of the distribution transformer in the above embodiments, an embodiment of this application provides a high-voltage side open circuit fault location system for a distribution transformer, the system comprising: The drop-out fuse monitoring unit is installed on the high-voltage side of the transformer and is configured to collect high-voltage side monitoring data of the transformer at multiple times. The multiple times include the current time and multiple times within the first monitoring period before the current time. The high-voltage side monitoring data includes the three-phase instantaneous voltage, the three-phase instantaneous current and the on / off status of the drop-out fuse on the high-voltage side. The terminal equipment, located on the low-voltage side of the transformer, is configured to collect low-voltage side monitoring data of the transformer at multiple times; the low-voltage side monitoring data includes the three-phase instantaneous voltage and the three-phase instantaneous current on the low-voltage side. The controller is communicatively connected to the drop-out fuse monitoring unit and the terminal equipment, and is configured to perform the steps of the above-described method for locating faults on the high-voltage side of the distribution transformer.

[0052] Please refer to Figure 2 In one embodiment of this application, the high-voltage side open circuit fault location system of the distribution transformer further includes a power supply circuit for the drop-out fuse monitoring unit. The power supply circuit includes: a CT power supply module, a rectifier module, an electrolytic capacitor C1, a DC-DC module, an LDO chip, a first switch, a battery, and a first voltage acquisition circuit. The CT power supply module is configured to draw power from the high-voltage side of the transformer. The output terminal of the CT power supply module is connected to the input terminal of the rectifier module, the output terminal of the rectifier module is connected to the input terminal of the DC-DC module, and an electrolytic capacitor C1 is connected in parallel to the output terminal of the rectifier module. The output of the DC-DC module is connected to the input of the LDO chip. The first voltage acquisition circuit is configured to detect the output voltage of the DC-DC module, and the output of the first voltage acquisition circuit is connected to the first signal input of the controller. The battery output is connected to the input of the LDO chip via a first switch. The control terminal of the first switch is connected to the first signal output of the controller. The output of the LDO chip is used to power the drop-out fuse monitoring unit.

[0053] In this embodiment, the power supply circuit of the drop-out fuse monitoring unit adopts a combination of CT power supply and battery power supply, which can save battery power and extend battery life. Specifically, the CT power supply module can draw power from the high-voltage side bus of the transformer, which is rectified by the rectifier module, filtered and regulated by capacitor C1, and then sent to the DC-DC module for voltage conversion. When the high-voltage side line is operating under normal load, the output voltage of the DC-DC module is relatively high; when the line is unloaded, under maintenance, or with extremely low load, the CT power supply will be low, resulting in a lower output voltage of the DC-DC module.

[0054] To ensure reliable power supply to the drop-out fuse monitoring unit, this embodiment includes a first voltage acquisition circuit for detecting the output voltage of the DC-DC module. When the output voltage of the DC-DC module exceeds a preset first power supply threshold (e.g., 3.3V), the controller outputs a low-level control signal G1 to the control terminal of the first switch (MOSFET Q1), opening the first switch and allowing the output voltage of the DC-DC module to power the LDO chip. The LDO chip then outputs a stable voltage to power the drop-out fuse monitoring unit. When the detected output voltage of the DC-DC module is less than a preset second power supply threshold (e.g., 2.5V), the controller outputs a high-level control signal G1 to the control terminal of the first switch, closing the first switch and allowing the battery B1 to power the LDO chip. The LDO chip then outputs a stable voltage to power the drop-out fuse monitoring unit. Simultaneously, the controller can also output an enable signal EN to the enable control terminal of the DC-DC module, disabling the DC-DC module from operation.

[0055] In this circuit, resistor R1 is the gate current-limiting resistor for MOSFET Q1. The first voltage acquisition circuit includes resistors R9 and R10. The first terminal of resistor R9 is connected to the output voltage of the DC-DC module, and the second terminal of resistor R9 is grounded through resistor R10. The voltage division of resistor R10 is proportional to the output voltage of the DC-DC module. The second terminal of resistor R9 is the output terminal of the first acquisition circuit. Connecting the second terminal of resistor R9 (labeled AD_V1) to the first signal input terminal of the controller allows the controller to obtain the output voltage of the DC-DC module by reading the voltage at the first signal input terminal. Furthermore, a diode D1 is provided at the output terminal of the DC-DC module to prevent current from battery B1 from flowing back into the DC-DC module when the first switch is turned on.

[0056] Please refer to Figure 2 In one embodiment of this application, the power supply circuit further includes a supercapacitor C2, a second switch, a third switch, a second voltage acquisition circuit, and a third voltage acquisition circuit; The output of the rectifier module is connected to the first terminal of the supercapacitor C2 via the second switch and the third switch in sequence, and the second terminal of the supercapacitor C2 is grounded; both ends of the second switch and the third switch are equipped with anti-parallel diodes, and the conduction directions of the two anti-parallel diodes are opposite. The second voltage acquisition circuit is configured to detect the voltage across the electrolytic capacitor C1, and the third voltage acquisition circuit is configured to detect the voltage across the supercapacitor C2. The output of the second voltage acquisition circuit is connected to the second signal input of the controller, and the output of the third voltage acquisition circuit is connected to the third signal input of the controller. The control terminal of the second switch is connected to the second signal output terminal of the controller, and the control terminal of the third switch is connected to the third signal output terminal of the controller.

[0057] In this embodiment, the second voltage acquisition circuit is used to detect the voltage across the electrolytic capacitor C1. When the voltage across the electrolytic capacitor C1 is greater than the preset first charging threshold voltage, it indicates that the CT has sufficient power. At this time, the controller can output a high-level control signal G2 to the control terminal of the second switch (MOSFET Q2) and a low-level control signal G3 to the control terminal of the third switch (MOSFET Q3). The second switch is turned on and the third switch is turned off. The voltage stored in the electrolytic capacitor C1 charges the supercapacitor C2 sequentially through the anti-parallel diodes of the second and third switches, storing excess energy in the supercapacitor C2. When the voltage across the electrolytic capacitor C1 is less than the preset second charging threshold voltage, it indicates that the CT has insufficient power. At this time, the controller can output a low-level control signal G2 to the control terminal of the second switch, turning off the second switch and stopping the charging of the supercapacitor C2. The second charging threshold voltage is less than the first charging threshold voltage; for example, the first charging threshold voltage can be 3.5V and the second charging threshold voltage can be 3.0V.

[0058] The third voltage acquisition circuit is used to detect the voltage across the supercapacitor C2. When the voltage across the electrolytic capacitor C1 is less than the third charging threshold voltage (e.g., 2.7V) and the voltage across the supercapacitor C2 is greater than the first discharge threshold voltage (e.g., 2.7V), it indicates that the power draw of the CT power module is insufficient, but the supercapacitor C2 has sufficient energy. At this time, the controller can output a low-level control signal G2 to the control terminal of the second switch (MOSFET Q2) and a high-level control signal G3 to the control terminal of the third switch (MOSFET Q3). The second switch is turned off and the third switch is turned on. The energy stored in the supercapacitor C2 charges the electrolytic capacitor C1 sequentially through the third switch and the anti-parallel diode of the second switch, ensuring that the electrolytic capacitor C1 can supply power to the drop-out fuse monitoring unit. When the voltage across the supercapacitor C2 is less than the second discharge threshold voltage (e.g., 2.5V), it indicates that the energy stored in the supercapacitor C2 is insufficient. At this time, the controller outputs a low-level control signal G3 to the control terminal of the third switch (MOSFET Q3). The third switch is turned off, stopping the discharge of the supercapacitor C2. Among them, resistors R2 and R3 are both current-limiting resistors.

[0059] Therefore, the supercapacitor C2 in this embodiment can store electrical energy when the high-voltage side load is high and the CT power supply module has surplus power, and when the high-voltage side load is low and the CT power supply module has insufficient power, the supercapacitor C2 can provide short-term buffer power supply, reducing the frequency of battery switching and further extending the battery life.

[0060] The second voltage acquisition circuit includes resistors R5 and R6. The first end of resistor R5 is connected to the first end of electrolytic capacitor C1, and the second end of resistor R5 is grounded through resistor R6. The voltage drop across resistor R6 is proportional to the voltage across electrolytic capacitor C1. The second end of resistor R5 is the output terminal of the second acquisition circuit. The second end of resistor R5 (labeled AD_V2) is connected to the second signal input terminal of the controller. The controller can obtain the voltage across electrolytic capacitor C1 by reading the voltage at the second signal input terminal.

[0061] The third voltage acquisition circuit includes resistors R7 and R8. The first end of resistor R7 is connected to the first end of supercapacitor C2, and the second end of resistor R7 is grounded through resistor R8. The voltage drop across resistor R8 is proportional to the voltage across supercapacitor C2. The second end of resistor R7 is the output terminal of the third acquisition circuit. The second end of resistor R7 (labeled AD_V3) is connected to the third signal input terminal of the controller. The controller can obtain the voltage across supercapacitor C2 by reading the voltage at the third signal input terminal.

[0062] Please refer to Figure 2 In one embodiment of this application, the high-voltage side open circuit fault location system of the distribution transformer further includes a fourth switch, which is connected in parallel to the output terminal of the CT power supply module, and the control terminal of the fourth switch is connected to the fourth signal output terminal of the controller.

[0063] In this embodiment, the second voltage acquisition circuit is used to detect the voltage across the electrolytic capacitor C1. When the voltage across the electrolytic capacitor C1 is less than 3.5V, it indicates that the CT power supply module is drawing power normally, and the controller can output a low-level control signal G4 to the control terminal of the fourth switch (MOSFET Q4), and the fourth switch is turned off. When the voltage across the electrolytic capacitor C1 is greater than the preset power supply voltage threshold (e.g., 3.7V), it indicates that the high-voltage side line is overloaded, causing the CT power supply to be too high. At this time, the controller can output a high-level control signal G4 to the control terminal of the fourth switch, and the fourth switch is turned on, short-circuiting the output side of the CT power supply module to discharge energy, clamping the voltage of the preceding stage, and preventing the subsequent stage devices from being damaged by overvoltage.

[0064] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for locating a high-voltage side open-circuit fault in a distribution transformer, characterized in that, include: Obtain the disconnection detection enable flag; If the disconnection detection enable flag is enabled, then high-voltage side monitoring data and low-voltage side monitoring data of the transformer at multiple times are acquired; the multiple times include the current time and multiple times within the first monitoring period before the current time; the high-voltage side monitoring data includes the high-voltage side three-phase instantaneous voltage, the high-voltage side three-phase instantaneous current and the on / off state of the drop-out fuse; the low-voltage side monitoring data includes the low-voltage side three-phase instantaneous voltage and the low-voltage side three-phase instantaneous current. The amplitude of the three-phase voltage on the high-voltage side is determined based on the instantaneous three-phase voltage on the high-voltage side at multiple times; the amplitude of the three-phase current on the high-voltage side is determined based on the instantaneous three-phase current on the high-voltage side at multiple times; and the status monitoring results of the drop-out fuse are determined based on the closing / opening status of the drop-out fuse at multiple times. The amplitude and phase of the three-phase voltage on the low-voltage side are determined based on the instantaneous three-phase voltage on the low-voltage side at multiple moments, and the amplitude of the three-phase current on the low-voltage side is determined based on the instantaneous three-phase current on the low-voltage side at multiple moments. If the status monitoring result of the drop-out fuse shows that the drop-out fuse is in the closed state and meets the first preset condition, then the fault location of the high-voltage side of the transformer is performed based on the amplitude and phase of the three-phase voltage on the low-voltage side. Wherein, if the amplitude of the three-phase current on the high-voltage side is greater than a preset current threshold, the first preset condition includes: the amplitude of the three-phase voltage on the high-voltage side is greater than a preset voltage threshold, and the error between the amplitude of the converted current of each phase and the amplitude of the low-voltage side current of the corresponding phase is within a preset error range; the amplitude of the converted current of each phase is obtained by converting the amplitude of the high-voltage side current of the corresponding phase to the low-voltage side based on a preset current ratio.

2. The method for locating a high-voltage side open-circuit fault in a distribution transformer as described in claim 1, characterized in that, If the amplitudes of the three-phase currents on the high-voltage side are all less than a preset current threshold, the first preset condition includes: The amplitudes of the three-phase voltages on the high-voltage side are all greater than the preset voltage threshold, and the amplitudes of the three-phase voltages on the low-voltage side are equal, with a phase difference of 120°.

3. The method for locating a high-voltage side open-circuit fault in a distribution transformer as described in claim 1, characterized in that, The determination of the status monitoring results of the drop-out fuse based on the closed / open state of the drop-out fuse at multiple times includes: From the multiple times the drop-out fuse's closed / open state, select the most recent N times the closed / open state of the drop-out fuse; If the closed / open state of the drop-out fuse is closed for the most recent N times, then the state monitoring result of the drop-out fuse is determined to be closed. Otherwise, the status monitoring result of the drop-out fuse is determined to be in the vacancy state.

4. The method for locating a high-voltage side open-circuit fault in a distribution transformer as described in claim 1, characterized in that, The method for locating open-circuit faults on the high-voltage side of a transformer based on the amplitude and phase of the three-phase voltage on the low-voltage side includes: The amplitude coefficient of each phase voltage is calculated based on the amplitude of each phase voltage and the preset rated voltage amplitude. Calculate the phase difference between each pair of adjacent phase voltages to obtain three phase differences between phases; Based on the amplitude coefficient of each phase voltage and the phase difference between the three phases, a preset feature library is searched to obtain the fault location information of the high-voltage side of the transformer. The preset feature library includes the correspondence between the amplitude coefficient of each phase voltage, the phase difference between the three phases and the fault location results. The fault location information includes the phase of the fault and the location of the fault. The fault location result on the high-voltage side of the transformer is determined based on the fault location information.

5. The method for locating a high-voltage side open-circuit fault in a distribution transformer as described in claim 4, characterized in that, The determination of the fault location result on the high-voltage side of the transformer based on the fault location information includes: If the fault location information indicates that there is a fault on the high-voltage side of the transformer, then the current amplitude of the faulty phase and the zero-sequence current on the low-voltage side are obtained. If the current amplitude of the disconnected phase is greater than the preset short-circuit current threshold, or the zero-sequence current on the low-voltage side is greater than the preset zero-sequence current threshold, then the fault location result of the high-voltage side of the transformer is determined to be no fault, and the fault detection enable flag is set to the disabled state. Otherwise, the fault location information is determined as the fault location result of the high-voltage side of the transformer.

6. The method for locating a high-voltage side open-circuit fault in a distribution transformer as described in claim 5, characterized in that, Also includes: If the disconnection detection enable flag is disabled, and within the preset second monitoring period, the amplitude of the three-phase current on the low-voltage side and the zero-sequence current on the low-voltage side meet the second preset condition, then the disconnection detection enable flag is set to enabled. The second preset condition is that the amplitude of the three-phase current on the low-voltage side is less than or equal to the preset short-circuit current threshold, and the zero-sequence current on the low-voltage side is less than or equal to the preset zero-sequence current threshold.

7. A fault location system for a high-voltage side open circuit of a distribution transformer, characterized in that, include: A drop-out fuse monitoring unit is installed on the high-voltage side of the transformer and is configured to collect high-voltage side monitoring data of the transformer at multiple times. The multiple times include the current time and multiple times within a first monitoring period before the current time. The high-voltage side monitoring data includes the high-voltage side three-phase instantaneous voltage, the high-voltage side three-phase instantaneous current, and the on / off status of the drop-out fuse. The terminal equipment, located on the low-voltage side of the transformer, is configured to collect low-voltage side monitoring data of the transformer at multiple times; the low-voltage side monitoring data includes the three-phase instantaneous voltage and the three-phase instantaneous current on the low-voltage side. A controller is communicatively connected to both the drop-out fuse monitoring unit and the terminal device, and the controller is configured to perform the steps of the method according to any one of claims 1 to 6.

8. The fault location system for high-voltage side open circuit of a distribution transformer as described in claim 7, characterized in that, It also includes the power supply circuit of the drop-out fuse monitoring unit, the power supply circuit including: CT power supply module, rectifier module, electrolytic capacitor C1, DC-DC module, LDO chip, first switch, battery and first voltage acquisition circuit; The CT power supply module is configured to draw power from the high-voltage side of the transformer. The output terminal of the CT power supply module is connected to the input terminal of the rectifier module. The output terminal of the rectifier module is connected to the input terminal of the DC-DC module. The electrolytic capacitor C1 is connected in parallel to the output terminal of the rectifier module. The output terminal of the DC-DC module is connected to the input terminal of the LDO chip, and the first voltage acquisition circuit is configured to detect the output voltage of the DC-DC module. The output terminal of the first voltage acquisition circuit is connected to the first signal input terminal of the controller. The output terminal of the battery is connected to the input terminal of the LDO chip via the first switch. The control terminal of the first switch is connected to the first signal output terminal of the controller. The output terminal of the LDO chip is used to power the drop-out fuse monitoring unit.

9. The high-voltage side open-circuit fault location system for distribution transformers as described in claim 8, characterized in that, The power supply circuit also includes a supercapacitor C2, a second switch, a third switch, a second voltage acquisition circuit, and a third voltage acquisition circuit; The output terminal of the rectifier module is connected to the first terminal of the supercapacitor C2 via the second switch and the third switch in sequence, and the second terminal of the supercapacitor C2 is grounded; both ends of the second switch and the third switch are provided with anti-parallel diodes, and the conduction directions of the two anti-parallel diodes are opposite. The second voltage acquisition circuit is configured to detect the voltage across the electrolytic capacitor C1, and the third voltage acquisition circuit is configured to detect the voltage across the supercapacitor C2. The output terminal of the second voltage acquisition circuit is connected to the second signal input terminal of the controller, and the output terminal of the third voltage acquisition circuit is connected to the third signal input terminal of the controller. The control terminal of the second switch is connected to the second signal output terminal of the controller, and the control terminal of the third switch is connected to the third signal output terminal of the controller.

10. The fault location system for high-voltage side open circuit of a distribution transformer as described in claim 8, characterized in that, It also includes a fourth switch and a second voltage acquisition circuit; The second voltage acquisition circuit is configured to detect the voltage across the electrolytic capacitor C1, and the output of the second voltage acquisition circuit is connected to the second signal input of the controller. The fourth switch is connected in parallel to the output terminal of the CT power supply module, and the control terminal of the fourth switch is connected to the fourth signal output terminal of the controller.

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