Internal broken line grounding fault identification method of Dyn wiring mode distribution transformer

Abstract

The invention belongs to the field of power supply and distribution, and particularly relates to a method for monitoring and identifying a broken line grounding fault in a high-voltage winding of a distribution transformer in a Dyn wiring mode in real time. The method comprises the following steps: S1, monitoring high-voltage side zero-sequence voltage and low-voltage side voltage data of the distribution transformer in real time; s2, obtaining high-voltage side zero-sequence voltage data, and setting the high-voltage side zero-sequence voltage data as a judgment basis 1; s3, synchronously collecting three-phase voltage of a low-voltage side, and designing a judgment basis 2; and S4, in combination with the judgment basis 1 and the judgment basis 2, diagnosing the internal condition of the high-voltage winding in the corresponding transformer, and correspondingly prompting the fault condition. High-voltage side data are collected through a voltage transformer, and low-voltage side data are collected in real time through an existing port meter or a low-voltage fusion terminal. Zero-sequence voltage is calculated through high-voltage-side three-phase voltage data collected by a voltage transformer, or the zero-sequence voltage is directly measured through a secondary circuit opening triangle of the voltage transformer, and generation of the high-voltage-side zero-sequence voltage serves as a starting condition.

Description

Technical Field

[0001] This invention belongs to the field of power supply and distribution, specifically a method for real-time monitoring and identification of open-circuit grounding faults inside the high-voltage winding of a distribution transformer with Dyn wiring configuration. Background Technology

[0002] Currently, most medium-voltage distribution networks (20kV / 10kV) are low-current grounding systems. When a single-phase grounding fault occurs on a feeder, the three-phase voltages will change, with the voltage of the faulty phase decreasing and the voltages of the other two phases increasing.

[0003] Existing distribution automation terminals require that the zero-sequence voltage and zero-sequence current amplitudes meet the standards and the duration of the faults be sufficient to trigger an alarm and send it to the master station for single-phase grounding fault detection in the distribution network.

[0004] When only discontinuous zero-sequence voltage and zero-sequence current signals are present, the terminal alarm cannot be triggered. The control department can monitor the zero-sequence voltage of the entire busbar in real time through the substation's grounding alarm device. For medium-voltage feeders in substations that have undergone grounding fault location device upgrades, the feeder where the grounding occurs can be accurately determined when the grounding current reaches a certain value. Sometimes, three-phase asynchronous closing and operation mode adjustments in the distribution network may also generate zero-sequence voltage and current. Alarm parameter settings need to exclude interference from similar situations (such as common alarm settings: zero-sequence voltage 2000V, zero-sequence current 2A, duration 2 seconds). Sometimes, even if the substation or distribution automation terminal's grounding alarm can be triggered, it can only indicate the feeder or branch where the fault is located, and cannot accurately locate the distribution transformer on the line and simultaneously determine the fault location.

[0005] Actual cases have shown that when a single-phase ground fault occurs inside the high-voltage winding of a distribution transformer, the three-phase voltage change trend is not consistent with the typical single-phase ground fault voltage; that is, one phase voltage decreases significantly while the other two phase voltages increase significantly. Because of the presence of insulating media (such as transformer oil, insulating components, etc.) in the grounding circuit, the voltage amplitude of the fault phase will not decrease to zero, and a phase deviation will occur, causing the voltage amplitudes of the other two phases to change differently (not increasing simultaneously). At this time, the electrical characteristic values ​​of the fault (zero-sequence voltage and zero-sequence current) cannot meet the requirements for triggering alarms on the distribution automation terminal or the substation grounding device, posing a safety hazard that could lead to the escalation of the accident. Therefore, a new technical solution needs to be designed to meet practical application needs, enabling real-time monitoring and identification of high-voltage winding open-circuit grounding faults in distribution transformers, and issuing alarms in the early stages of fault development to prevent the accident from escalating and ensure the safety of the distribution network lines and equipment. Summary of the Invention

[0007] This invention proposes a method that can accurately alarm for open-circuit grounding faults inside distribution transformers by real-time monitoring of the high-voltage winding operation status. The alarm is issued in the early stage of fault development to prevent the accident from escalating, ensure the safety of distribution network lines and equipment, and fill the monitoring blind spot of traditional single-phase grounding alarm technology for distribution networks.

[0008] When a break in the high-voltage winding of a distribution transformer (Dyn connection type) causes a ground fault, a significant voltage change occurs on the high-voltage side, generating a zero-sequence voltage. Simultaneously, the low-voltage side voltage also changes significantly. Due to the break in one phase, the high-voltage winding phase cannot generate an induced electromotive force, and the corresponding low-voltage winding phase voltage is zero. Initially, the fault symptoms after the break and ground fault are not obvious and may not trigger relevant protection alarms. However, the fault risks escalating over time. This solution can accurately identify and issue alarms in the early stages of fault development, ensuring the safety of the distribution network's lines and equipment.

[0009] The method for identifying internal open-circuit grounding faults in Dyn-connected distribution transformers of the present invention is as follows:

[0010] S1. Real-time monitoring of zero-sequence voltage on the high-voltage side and voltage on the low-voltage side of the distribution transformer;

[0011] S2. Obtain the zero-sequence voltage data on the high-voltage side and set it as the judgment criterion 1;

[0012] S3. Synchronously collect the three-phase voltage on the low-voltage side and design judgment criterion 2;

[0013] S4. Based on judgment criteria 1 and judgment criteria 2, diagnose the internal condition of the high-voltage winding of the corresponding transformer and provide corresponding prompts in case of fault.

[0014] Furthermore, in S1, high-voltage side data is acquired through voltage transformers (hereinafter referred to as PT acquisition), while low-voltage side data is acquired in real time through existing gate meters or low-voltage fusion terminals.

[0015] The aforementioned meters or low-voltage fusion terminals are all commercially available products.

[0016] Furthermore, in S2, the zero-sequence voltage is calculated from the three-phase voltage data of the high-voltage side collected by the voltage transformer, or the zero-sequence voltage is directly measured through the open delta of the secondary circuit of the voltage transformer. The generation of the zero-sequence voltage on the high-voltage side is used as the starting condition, and the value of the zero-sequence voltage is used as the judgment basis 1.

[0017] The starting conditions can be adjusted according to the actual situation, such as the zero-sequence voltage being adjustable from 1 to 6 kV.

[0018] Furthermore, in S3, the three-phase voltage on the low-voltage side is collected synchronously. The phase with zero low-voltage phase corresponding to the high-voltage fault phase winding is set as phase a, and the other two phases are phase b and phase c, respectively. The voltage of phase a is significantly lower than that of phase b and phase c.

[0019] According to the formula for the effective value of induced electromotive force: Where E is the induced electromotive force, f is the power frequency, and N is the number of turns in the winding. For magnetic flux, if there is no induced voltage in the high-voltage side winding, then there is no induced electromotive force in the corresponding winding, and correspondingly, there is no induced voltage on the low-voltage side. The three-phase voltages on the low-voltage side can be combined in the following ways, and the corresponding numerical values ​​for each combination are used as the basis for judgment 2.

[0020] The three-phase voltage on the side has the following combinations, and the corresponding numerical values ​​for each combination are used as the basis for judgment 2.

[0021] Because the line voltage of the distribution network remains three-phase symmetrical when a single-phase ground fault occurs, the non-faulty distribution transformers on the line can operate normally, and the voltage and current on the low-voltage side are both within normal range.

[0022] Furthermore, in S4, the judgment criteria 1 for the zero-sequence voltage on the high-voltage side and the judgment criteria 2 for the three-phase voltage on the low-voltage side are compared. If both occur simultaneously and the corresponding values ​​meet the conditions, it is determined that there is a fault point in the high-voltage winding inside the transformer, i.e., a grounding point. At this time, an alarm message is sent to the operation and maintenance personnel to assist the site in eliminating the fault as soon as possible.

[0023] An electronic device includes one or more processors for storing one or more programs, which, when executed by the one or more processors, cause the one or more processors to perform the aforementioned method for identifying internal open-circuit grounding faults in Dyn-connected distribution transformers.

[0024] A storage medium storing a computer program, wherein the computer program is configured to execute the aforementioned method for identifying internal open-circuit grounding faults in a Dyn-connected distribution transformer when it is run.

[0025] This invention uses the generation of zero-sequence voltage on the high-voltage side as the starting condition to avoid false alarms caused by voltage changes on the low-voltage side due to non-transformer body faults, and comprehensively judges whether it is a transformer high-voltage winding open-circuit grounding fault.

[0026] Compared with the prior art, the present invention has the following characteristics:

[0027] (1) By real-time detection of the zero-sequence voltage value on the line side and the three-phase voltage value on the low-voltage side of the distribution transformer, and by comparing and verifying the two, the verification method is the technical solution and implementation case mentioned above. The comparison result is used to determine whether there is a single-phase open-circuit grounding fault in the high-voltage winding of the transformer.

[0028] (2) This method has a high fault tolerance rate, that is, the zero-sequence voltage value and the three-phase voltage value on the low-voltage side for comparison and verification do not need to be strictly consistent in the time of occurrence, as long as they can be detected within a certain period.

[0029] (3) The zero-sequence voltage used for comparison can be collected by the incoming line cabinet installed on the high-voltage side of the transformer body, or by directly collecting the zero-sequence voltage on other distribution automation terminals of the line, or by collecting it through the substation grounding alarm device. The three-phase voltage on the low-voltage side can be directly collected on-site by the transformer gate meter or the integrated terminal, or by real-time measurement through the main station.

[0030] (4) Coil equipment with a structure similar to a distribution transformer, i.e., equipment with multi-phase high and low voltage windings, can be monitored in real time by this method to determine whether there is a single-phase open-circuit grounding fault. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a medium-voltage distribution network feeder in an embodiment of the method for identifying internal open-circuit grounding faults in a Dyn-connected distribution transformer of the present invention;

[0032] Figure 2 This is a schematic diagram of an internal open-circuit grounding fault identification method for a distribution transformer using the Dyn wiring method of the present invention.

[0033] Figure 3 This is a schematic diagram of the line-side voltage phasor before an internal open-circuit grounding fault in a distribution transformer, as described in an embodiment of the method for identifying internal open-circuit grounding faults in a Dyn-connected distribution transformer of the present invention.

[0034] Figure 4 This is a schematic diagram of the line-side voltage phasor after an internal open-circuit grounding fault in a distribution transformer according to an embodiment of the method for identifying internal open-circuit grounding faults in a Dyn-connected distribution transformer of the present invention.

[0035] Figure 5 This is a schematic diagram of the workflow of the method for identifying internal open-circuit grounding faults in a Dyn-connected distribution transformer according to the present invention.

[0036] Figure 6 This is the equivalent circuit diagram of the induced electromotive force in the method for identifying internal open-circuit grounding faults in a Dyn-connected distribution transformer of the present invention. Detailed Implementation

[0037] See attached document Figures 1-6 The present invention provides a further explanation of the method for identifying internal open-circuit grounding faults in a Dyn-connected distribution transformer.

[0038] The technical solutions in the embodiments of the present invention have been clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] See attached document Figure 5 The method for identifying internal open-circuit grounding faults in Dyn-connected distribution transformers is as follows:

[0040] S1. Real-time monitoring of zero-sequence voltage on the high-voltage side and voltage on the low-voltage side of the distribution transformer;

[0041] S2. Obtain the zero-sequence voltage data on the high-voltage side and set it as the judgment criterion 1;

[0042] S3. Synchronously collect the three-phase voltage on the low-voltage side and design judgment criterion 2;

[0043] S4. Based on judgment criteria 1 and judgment criteria 2, diagnose the internal condition of the high-voltage winding of the corresponding transformer and provide corresponding prompts in case of fault.

[0044] Furthermore, in S1, high-voltage side data is acquired through voltage transformers (hereinafter referred to as PT acquisition), while low-voltage side data is acquired in real time through existing gate meters or low-voltage fusion terminals.

[0045] The aforementioned meters or low-voltage fusion terminals are all commercially available products.

[0046] Furthermore, in S2, the zero-sequence voltage is calculated from the three-phase voltage data of the high-voltage side collected by the voltage transformer, or the zero-sequence voltage is directly measured through the open delta of the secondary circuit of the voltage transformer. The generation of the zero-sequence voltage on the high-voltage side is used as the starting condition, and the value of the zero-sequence voltage is used as the judgment basis 1.

[0047] The starting conditions can be adjusted according to the actual situation, such as the zero-sequence voltage being adjustable from 1 to 6 kV.

[0048] Furthermore, in S3, the three-phase voltage on the low-voltage side is collected synchronously. The phase with zero low-voltage phase corresponding to the high-voltage fault phase winding is set as phase a, and the other two phases are phase b and phase c, respectively. The voltage of phase a is significantly lower than that of phase b and phase c.

[0049] According to the appendix Figure 6 Equivalent circuit diagram and formula for the effective value of induced electromotive force: (E is the induced electromotive force, f is the power frequency, and N is the number of turns in the winding) (For magnetic flux), if there is no induced voltage in the high-voltage side winding, then there is no induced electromotive force in the corresponding winding, and correspondingly, there is no induced voltage on the low-voltage side. The three-phase voltages on the low-voltage side can be combined in the following ways, and the corresponding numerical values ​​for each combination are used as the basis for judgment 2.

[0050] Because the line voltage of the distribution network remains three-phase symmetrical when a single-phase ground fault occurs, the non-faulty distribution transformers on the line can operate normally, and the voltage and current on the low-voltage side are both within normal range.

[0051] Furthermore, in S4, the judgment criteria 1 for the zero-sequence voltage on the high-voltage side and the judgment criteria 2 for the three-phase voltage on the low-voltage side are compared. If both occur simultaneously and the corresponding values ​​meet the conditions, it is determined that there is a fault point in the high-voltage winding inside the transformer, i.e., a grounding point. At this time, an alarm message is sent to the operation and maintenance personnel to assist the site in eliminating the fault as soon as possible.

[0052] An electronic device includes one or more processors for storing one or more programs, which, when executed by the one or more processors, cause the one or more processors to perform the aforementioned method for identifying internal open-circuit grounding faults in Dyn-connected distribution transformers.

[0053] A storage medium storing a computer program, wherein the computer program is configured to execute the aforementioned method for identifying internal open-circuit grounding faults in a Dyn-connected distribution transformer when it is run.

[0054] Example

[0055] Currently, a large number of distribution transformers are in operation in the power system, most of which are Dyn11 connected. Transformer failures leading to feeder faults occur frequently, causing significant losses to the power system and users. The method proposed in this invention fills the monitoring blind spot of traditional single-phase grounding alarm technology for distribution networks. It can monitor the operating status of the high-voltage windings of distribution transformers in real time, accurately alarm for single-phase open-circuit grounding faults in distribution transformers, and issue alarms in the early stages of fault development to prevent the accident from escalating and ensure the safety of distribution network lines and equipment.

[0056] See attached document Figure 1 For example, in the above schematic diagram of medium-voltage distribution network feeders, a section of the substation busbar has multiple medium-voltage 10 kV outgoing lines A, B, C, etc.

[0057] Taking outgoing line A as an example, the line has multiple branch lines, each with multiple distribution transformers. If a high-voltage winding of one of these transformers (let's assume it's transformer number 02, with a Dyn connection) experiences a ground fault, the system will generate zero-sequence voltage and zero-sequence current in the early stages of the fault. However, at this point, both amplitudes are too small to trigger the distribution automation terminal and the ground fault alarm in the substation. If the zero-sequence voltage meets the conditions but the zero-sequence current is too small, it may only indicate an abnormality in the substation bus voltage, without being able to pinpoint the feeder or branch line (at this time, all automation terminals on the feeder of that bus section will detect the zero-sequence voltage). When both the zero-sequence voltage and zero-sequence current values ​​simultaneously meet the conditions to trigger a single-phase ground fault alarm, the alarm information sent by the field terminal can only pinpoint the feeder or branch line, not the faulty distribution transformer.

[0058] When a single-phase open-circuit ground fault occurs in the high-voltage winding of a transformer, a zero-sequence voltage will be generated on the high-voltage line side. Simultaneously, the low-voltage side voltage will also change significantly. Due to the open circuit, one phase of the high-voltage winding cannot generate an induced electromotive force, and the corresponding low-voltage winding phase voltage is zero. When the zero-sequence voltage is detected on the line side of the distribution transformer, the three-phase low-voltage voltage can be collected.

[0059] The magnitude of the zero-sequence voltage is calculated and judgment criterion 1 is generated. At the same time, the three-phase voltage values ​​on the low-voltage side are collected. If there is a phase voltage of zero, judgment criterion 2 is generated.

[0060] When both Judgment Criterion 1 and Judgment Criterion 2 are generated simultaneously, it can be determined that there is a grounding fault with a broken wire inside the distribution transformer.

[0061]

[0062] Traditional single-phase ground fault detection in distribution networks primarily relies on determining whether the zero-sequence voltage and current on the high-voltage side meet certain conditions to trigger an alarm and send it to the main station. The detection range is generally limited to the feeder or branch line where the fault occurs. When a single-phase open-circuit ground fault occurs in the high-voltage winding inside a distribution transformer, the grounding point exhibits non-metallic grounding due to the presence of insulating media such as air or insulating oil within the transformer. The voltage on the line side of the faulted phase will not drop to zero, and zero-sequence voltage and current will be generated simultaneously. This zero-sequence component cannot accurately trigger a ground fault alarm on the line, and even if an alarm is triggered, the distribution transformer on the line cannot be accurately located.

Claims

1. A method for identifying internal open-circuit grounding faults in a Dyn-connected distribution transformer, characterized in that, S1. Real-time monitoring of zero-sequence voltage on the high-voltage side and voltage on the low-voltage side of the distribution transformer; S2. Obtain the zero-sequence voltage data on the high-voltage side and set it as the judgment criterion 1; S3. Synchronously collect the three-phase voltage on the low-voltage side and design judgment criterion 2; S4. Based on judgment criteria 1 and judgment criteria 2, diagnose the internal condition of the high-voltage winding of the corresponding transformer and provide corresponding prompts in case of fault.

2. The method for identifying internal open-circuit grounding faults in a Dyn-connected distribution transformer according to claim 1, characterized in that, In S1, high-voltage side data is collected through voltage transformers, while low-voltage side data is collected in real time through existing inter-gate meters or low-voltage fusion terminals.

3. The method for identifying internal open-circuit grounding faults in a Dyn-connected distribution transformer according to claim 1, characterized in that, In S2, the zero-sequence voltage is calculated from the three-phase voltage data of the high-voltage side collected by the voltage transformer, or the zero-sequence voltage is directly measured through the open delta of the secondary circuit of the voltage transformer. The generation of the zero-sequence voltage on the high-voltage side is used as the starting condition, and the value of the zero-sequence voltage is used as the judgment basis 1.

4. The method for identifying internal open-circuit grounding faults in a Dyn-connected distribution transformer according to claim 3, characterized in that, The starting conditions are adjusted according to the actual situation, with the zero-sequence voltage being 1-6 kV.

5. The method for identifying internal open-circuit grounding faults in a Dyn-connected distribution transformer according to claim 1, characterized in that, In S3, the three-phase voltage on the low-voltage side is collected synchronously. The phase with zero low-voltage phase corresponding to the high-voltage fault phase winding is set as phase a, and the other two phases are phase b and phase c, respectively. The voltage of phase a is significantly lower than that of phase b and phase c. According to the formula for the effective value of induced electromotive force: E is the induced electromotive force, f is the power frequency, and N is the number of turns in the winding. For magnetic flux, if there is no induced voltage in the high-voltage side winding, then there is no induced electromotive force in the corresponding winding, and correspondingly, there is no induced voltage on the low-voltage side. The three-phase voltages on the low-voltage side have the following combinations, and the corresponding numerical values ​​for each combination are used as the basis for judgment 2; Because the line voltage of the distribution network remains three-phase symmetrical when a single-phase ground fault occurs, the non-faulty distribution transformers on the line can operate normally, and the voltage and current on the low-voltage side are both within normal range.

6. The method for identifying internal open-circuit grounding faults in a Dyn-connected distribution transformer according to claim 1, characterized in that, In S4, the judgment criteria 1 for the zero-sequence voltage on the high-voltage side and the judgment criteria 2 for the three-phase voltage on the low-voltage side are compared. If both occur simultaneously and the corresponding values ​​meet the conditions, it is determined that there is a fault point in the high-voltage winding inside the transformer, i.e., a grounding point. At this time, an alarm message is sent to the operation and maintenance personnel to assist the site in troubleshooting as soon as possible.

7. An electronic device comprising one or more processors for storing one or more programs, characterized in that, When the one or more programs are executed by the one or more processors, the one or more processors perform the aforementioned method for identifying internal open-circuit grounding faults in Dyn-connected distribution transformers.

8. A storage medium storing a computer program, characterized in that, in, The computer program is configured to execute the aforementioned method for identifying internal open-circuit grounding faults in Dyn-connected distribution transformers during runtime.

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