Transformer differential protection device and method for a substation integrated automation system

Abstract

The application discloses a transformer differential protection device and method of a substation comprehensive automation system. The device contains current collection, data processing, protection action and other modules, optimizes the current signal through phase correction and balance coefficient compensation algorithm, adopts two-section type ratio differential criterion combined with secondary harmonic braking, and accurately distinguishes internal faults and magnetizing inrush current. The device is matched with CT disconnection blocking and fault recording function, can dynamically adjust parameters, cooperates with the system through DL / T634.5104 protocol, realizes data uploading, remote control and alarm linkage. After the device is connected to the system, the protection action is fast in response and small in error, the recording data support background analysis, effectively avoids misoperation and refusal to operate, improves the operation reliability and operation and maintenance efficiency of the transformer, and is suitable for transformers of various voltage grades of 10kV-110kV.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology, and specifically relates to a transformer differential protection device and method suitable for substation integrated automation system, which is mainly applied to the main protection configuration of power transformers with voltage levels of 10kV-110kV. Background Technology

[0002] With the continuous advancement of the construction of new power systems, intelligent substations have become the core carriers of digital and intelligent operation and maintenance of power grids. Substation integrated automation systems are the core support platform for realizing "unmanned operation, remote control, and intelligent operation and maintenance" of substations. As the core hub equipment for power transmission and distribution in the power system, the safety and stability of power transformers directly determine the power supply reliability and power quality of the regional power grid. Once an internal short-circuit fault occurs, it can cause irreversible damage to equipment, or even lead to large-scale power outages, resulting in significant economic losses and social impact.

[0003] Longitudinal differential protection, with its advantages of fast operation, clear protection range, and high sensitivity, is the main protection for internal short-circuit faults in power transformers. Its core principle involves collecting secondary current signals from the current transformers (CTs) on each side of the transformer, performing phase correction and amplitude compensation, and then calculating the differential current. Whether the differential current exceeds the operating threshold is used as the core criterion for fault identification and tripping. Currently, the design, manufacturing, and engineering application of transformer differential protection in China must strictly adhere to national and industry mandatory standards such as GB / T14285-2006 "Technical Specification for Relay Protection and Safety Automatic Devices" and DL / T770-2012 "General Technical Conditions for Transformer Protection Devices." It must also be compatible with the communication protocol requirements of DL / T634.5104-2009 "Telecontrol Equipment and Systems Part 5-104: Transmission Protocol Adopting a Subset of Standard Transmission Protocols for Network Access in IEC60870-5-101," achieving standardized and collaborative integration with substation integrated automation systems.

[0004] Currently, the industry has conducted extensive research and engineering applications on transformer differential protection technology, resulting in a series of mature technical solutions. For example, Chinese invention patent CN106451354A discloses a transformer differential protection method and device; major domestic relay protection manufacturers have also launched a series of transformer differential protection devices, which are widely used in substations of various voltage levels in China.

[0005] However, under the practical engineering applications and the development needs of new power systems, the aforementioned existing technologies still have multiple unresolved technical bottlenecks, making it difficult to meet the core requirements of smart substations for transformer protection: "high reliability, high sensitivity, strong adaptability, and full-scenario collaboration." Specific shortcomings are as follows:

[0006] First, it is difficult to balance the anti-interference capability and sensitivity of fault identification criteria, which easily leads to false trips and failures to trip. Firstly, existing solutions mostly use single-stage fixed-ratio braking criteria, which cannot adapt to all operating conditions of the transformer: under light load conditions, the braking current is small, the protection sensitivity is insufficient, and it is easy to fail to trip for minor internal faults; under heavy load or external fault conditions, the unbalanced current generated by CT core saturation increases sharply, easily causing protection malfunctions. Secondly, the inrush current identification and braking scheme has inherent defects: existing technologies mostly use fixed second harmonic braking coefficients, which cannot adapt to the inrush current characteristics under different scenarios such as transformer energization, reclosing after fault clearing, and voltage fluctuations. When the second harmonic content of the inrush current is low, false trips are easy to occur; when the internal fault current contains second harmonic components, failure to trip is easy to occur, making it impossible to accurately distinguish between inrush current and internal fault current. Third, the ability to suppress unbalanced current is insufficient: the differences in wiring methods between the high and low voltage sides of the transformer, the inconsistency between the CT ratio and the core saturation characteristics, etc., will generate inherent unbalanced current. The phase correction and amplitude compensation logic of the existing scheme is not perfect and cannot completely eliminate the interference of unbalanced current on the protection criteria, further increasing the risk of false tripping.

[0007] Second, the collaborative protection capability under abnormal operating conditions is insufficient, which can easily lead to secondary power supply accidents. The existing technology of CT disconnection detection and differential protection lacks a deep collaborative mechanism: on the one hand, the CT disconnection detection logic is simple, and it is only judged by the disappearance of single-phase current, which is easily confused with single-phase grounding faults and load fluctuations, resulting in a high misjudgment rate and a large response delay; on the other hand, it cannot quickly block differential protection after disconnection, which can easily misjudge the differential current generated by the disconnection as an internal fault, causing unnecessary tripping accidents. Moreover, after the fault is cleared, manual on-site reset of the protection is required, and automatic recovery is not possible, which seriously affects the continuity of power supply.

[0008] Third, the protection parameters have poor adaptability and cannot match the real-time operating conditions of the transformer. The core protection parameters of the existing devices (differential current setting, braking current setting, second harmonic braking coefficient, etc.) are mostly factory-fixed settings or only support manual adjustment on site. They cannot be dynamically optimized and adjusted according to the real-time load level of the transformer, the frequency of inrush current, changes in CT secondary circuit parameters, etc., and cannot take into account the protection sensitivity and reliability under different operating scenarios. The ability to adapt to transformers of all voltage levels from 10kV to 110kV is insufficient.

[0009] Fourth, the fault tracing capability is insufficient and cannot support the needs of intelligent operation and maintenance. The fault recording function of the existing device has obvious shortcomings: low sampling rate and insufficient recording time, which cannot fully restore the current change characteristics of the entire fault process; the recorded data is mostly in a proprietary format, which is incompatible with the COMTRADE format commonly used in the power industry. It needs to be manually exported on-site and then imported into the substation automation system for analysis. It cannot realize the automatic uploading, remote viewing and centralized analysis of recorded data, resulting in low fault tracing efficiency and failing to meet the operation and maintenance needs of intelligent substations.

[0010] Fifth, the coordination with the substation integrated automation system is severely insufficient, making it unsuitable for unattended operation and maintenance. This is the most prominent disconnect between existing technology and the development needs of new power systems: First, most devices lack standardized communication protocol interface capabilities, making it impossible to achieve stable two-way data interaction with the substation integrated automation system. They can only unidirectionally upload a small number of fault alarm signals and cannot receive remote control commands and protection parameter setting instructions issued by the system. Core parameters need to be manually modified on-site, resulting in extremely low operation and maintenance efficiency. Second, telemetry data, operating status, and alarm signals cannot be synchronized to the automation system backend in real time, making it impossible for operation and maintenance personnel to remotely monitor the operating status of the devices and achieve early warning of abnormal operating conditions. Third, fault data and waveform recording files cannot be shared with the automation system, failing to support centralized and digital fault analysis and dispatching decisions of the power grid, and completely failing to meet the core operation and maintenance requirements of "unattended operation and remote control" for smart substations.

[0011] Although improvement solutions have emerged in the industry to address some of the aforementioned individual pain points, existing technologies still lack a comprehensive transformer differential protection solution that integrates "accurate fault identification under all operating conditions, dynamic adaptation of operating parameters, collaborative protection under abnormal operating conditions, and full-process fault tracing" with "deep collaboration with substation integrated automation systems." This solution cannot fully meet the high reliability, high sensitivity, strong adaptability, and remote intelligent operation and maintenance requirements of transformer protection in new power systems. Therefore, developing a transformer differential protection device and method with second harmonic braking that features scientific criteria, rapid response, strong adaptability, and full bidirectional data interaction with substation integrated automation systems has become an urgent technical problem to be solved in the field of power system relay protection, and also has significant engineering application value. Summary of the Invention

[0012] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a transformer differential protection device and method for a substation integrated automation system. It aims to solve the technical problems of traditional transformer differential protection, such as inability to accurately distinguish between inrush current and internal faults, easy false tripping or failure to trip, inability to dynamically adapt parameters, and poor coordination with the substation automation system, so as to achieve high reliability, high sensitivity and remote intelligent operation and maintenance of transformer protection.

[0013] To address the aforementioned technical problems, this invention provides a transformer differential protection device and method for a substation integrated automation system.

[0014] The specific details of the invention are as follows:

[0015] A transformer differential protection device for a substation integrated automation system includes a current acquisition module, a data processing module, a protection action module, and a communication module. The current acquisition module, the data processing module, and the protection action module are electrically connected in sequence, and the communication module is electrically connected to the data processing module.

[0016] The current acquisition module is equipped with a high-voltage side three-phase current acquisition terminal and a low-voltage side three-phase current acquisition terminal, which are used to acquire the secondary current signals of the high-voltage side and low-voltage side of the transformer and transmit them to the data processing module.

[0017] The communication module supports the DL / T634.5104 protocol and is used to achieve bidirectional data interaction with the substation integrated automation system, including uploading telemetry data, fault information, alarm signals and waveform data to the automation system, and receiving remote control commands and protection parameters issued by the automation system.

[0018] The data processing module is used for:

[0019] Phase correction and balance coefficient compensation are performed on the acquired high-voltage and low-voltage secondary current signals to obtain standardized current signals;

[0020] Calculating differential current based on standardized current signal and braking current ;

[0021] Extract the second harmonic component from the differential current and calculate the proportion of the second harmonic content. ;

[0022] Fault diagnosis is performed using a two-stage ratio differential criterion: when the braking current... Braking current setting When, if the differential current Differential current setting And the proportion of second harmonic content Second harmonic coefficient set value The fault was determined to be internal; when the braking current... Braking current setting At that time, if And the proportion of second harmonic content The fault was determined to be internal; among them Set the ratio braking coefficient to a fixed value;

[0023] The protection action module is used to output a trip signal and disconnect the switch on the corresponding side of the transformer when the data processing module determines that there is an internal fault.

[0024] Preferably, the differential current setting value The setting range is 0.10A-10.00A, and the braking current setting value is... Its setting range is 0.10A-10.00A, and it is compatible with current transformers with a rated input current of 5A / 1A; the ratio braking coefficient setting value is... The setting range is 0.30-0.70, and the second harmonic coefficient is set to... The setting range is 0.10-0.40, suitable for power transformers with voltage levels of 10kV-110kV; among which, the differential current setting value... The braking current setting is configured to avoid the maximum unbalanced current under the transformer's rated load. Set the transformer to 0.5-1 times its rated secondary current.

[0025] Preferably, it also includes a CT disconnection detection module, which is electrically connected to the data processing module, and the CT disconnection determination logic is executed before the differential fault determination criterion.

[0026] The CT disconnection detection module is used to detect the abrupt change characteristics of the current signal on the high-voltage side or the low-voltage side: when the current value of a certain phase on a certain side drops by ≥90% within 2 consecutive sampling cycles and drops to less than 5% of the rated current, while the current of other phases on this side and any phase current on the opposite side does not change by more than ±5%, it is determined that the CT is disconnected.

[0027] The data processing module blocks the trip output of the protection action module within 10ms after determining the CT disconnection, and pushes a time-stamped CT disconnection alarm signal to the substation integrated automation system through the communication module. When the disconnected phase current is detected to recover to more than 90% of the normal operating value, and there are no abnormalities for 3 consecutive sampling cycles, it is determined that the CT disconnection fault is cleared, the differential protection function is automatically restored, and the status is fed back to the automation system.

[0028] Preferably, the phase correction is suitable for For transformers with different wiring configurations, the standardized current signal on the high-voltage side passes through... The calculation yielded, where , , The high-voltage side three-phase secondary current sampling values; the low-voltage side standardized current signal is passed through... The calculation yielded, where , , These are the sampled values ​​of the three-phase secondary current on the low-voltage side; where This is the low-pressure side balance coefficient. These are the primary rated currents for the high and low voltage sides, respectively. The phase correction is performed based on the synchronous sampling data of the high and low voltage side CTs, respectively, with a sampling synchronization error ≤10μs.

[0029] Preferably, the differential current The braking current ;in This is the effective value of the phase current of the standardized current signal on the high-voltage side. This is the effective value of the phase current of the standardized current signal on the low-voltage side.

[0030] Preferably, the system further includes a fault recording module, which is electrically connected to the data processing module. This fault recording module is used to adjust the starting setpoint to the differential current setpoint when the differential current surge exceeds the starting setpoint. 0.5 times that of the CT disconnection determination period, the locked waveform recording is initiated;

[0031] The three-phase current sampling data is recorded at a sampling rate of 32 points per cycle for the 8 cycles before the fault and the 56 cycles after the fault. A COMTRADE format waveform file is generated within 5 seconds after the waveform recording is completed, and uploaded to the substation integrated automation system server through the communication module, supporting the background viewing and analysis of the automation system.

[0032] Preferably, the telemetry data uploaded by the communication module includes the RMS values ​​of the high-voltage side and low-voltage side currents, differential current, braking current, and the proportion of second harmonic content. The default upload cycle is 1 second, adaptively matching the data refresh cycle of the substation integrated automation system; telemetry data supports uploading across dead zones, with the dead zone value set to 0.2% of the rated value; the parameters received by the communication module from the automation system include the differential current setting. Braking current setting value Ratio braking coefficient set value and the second harmonic coefficient set value Parameter modification error .

[0033] A transformer differential protection method for a substation integrated automation system, based on the aforementioned differential protection device, includes core steps of current acquisition, data processing, and protection action, specifically:

[0034] Step 1: Acquire the three-phase secondary current signals of the high-voltage side and low-voltage side of the transformer through the current acquisition module and transmit them to the data processing module;

[0035] Step 2: The data processing module performs phase correction and balance coefficient compensation on the high-voltage and low-voltage secondary current signals respectively to obtain standardized current signals; wherein, the phase correction is for the Y / Δ11 connected transformer, and the high-voltage side standardized current signal is obtained through... Calculation, where , , The high-voltage side three-phase secondary current sampling values; the low-voltage side standardized current signal is passed through... Calculation, where , , These are the sampled values ​​of the three-phase secondary current on the low-voltage side; This is the low-pressure side balance coefficient. These are the primary rated currents for the high and low voltage sides, respectively. CT ratios for high and low pressure sides, respectively.

[0036] Step 3: Calculate the differential current based on the standardized current signal and braking current ,in This is the effective value of the phase current on the high-voltage side. This represents the effective value of the phase current on the low-voltage side.

[0037] Step 4: Extract the second harmonic component from the differential current and calculate the proportion of the second harmonic content. The It is the ratio of the effective value of the second harmonic component to the effective value of the fundamental component; and it calls the preset differential current setting. Braking current setting value Ratio braking coefficient set value and the second harmonic coefficient set value ;

[0038] Step 5: Use a two-stage ratio differential criterion to determine the fault type: when At that time, if and It was determined to be an internal fault; when At that time, if and The fault was determined to be internal.

[0039] Step 6: If the fault is determined to be internal, the protection action module outputs a trip signal to disconnect the corresponding switch on the transformer side; if the fault is not determined to be internal, return to step 1 for continued monitoring.

[0040] Furthermore, it also includes a CT disconnection collaborative protection step, and the CT disconnection determination logic takes precedence over the differential fault judgment in step 5, specifically:

[0041] While acquiring the current signal in step 1, the CT disconnection detection module monitors the abrupt change characteristics of the current signals of each phase on the high-voltage side and the low-voltage side in real time.

[0042] When a sudden drop of ≥90% in the current value of a certain phase on a certain side is detected within two consecutive sampling cycles, and the drop is less than 5% of the rated current, while the current of other phases on this side and any phase current on the opposite side does not change by more than ±5%, it is determined that the CT is disconnected.

[0043] The data processing module immediately blocks the trip output of the protection action module and generates a time-stamped CT disconnection alarm signal, which is then uploaded to the substation integrated automation system via the communication module.

[0044] When the current of the disconnected phase is detected to recover to more than 90% of the normal operating value, and there are no abnormalities for three consecutive sampling cycles, it is determined that the CT disconnection fault has been resolved, the differential protection function is automatically restored, and the status is fed back to the automation system.

[0045] Furthermore, it also includes a step for dynamic parameter adjustment:

[0046] Real-time monitoring of transformer operating conditions, including load current magnitude, frequency of inrush current occurrence, and changes in CT secondary circuit parameters, with monitoring data synchronously uploaded to the substation integrated automation system;

[0047] When the load current remains above 80% of the rated current for an extended period, the second harmonic coefficient should be set within the adjustment range. Reduce by 5%~10%; when the frequency of inrush current exceeds 3 times per month within a statistical period of 1 month, the second harmonic coefficient will be set within the adjustment range. Increase by 5%~10%; the inrush current determination criteria are as follows: Furthermore, the differential current has not reached the operating setpoint; the upper and lower limits of parameter adjustment shall not exceed the setting range specified above.

[0048] Based on the changes in the CT secondary circuit parameters, the balance coefficient is recalculated. After verification, the data is updated to the data processing module, and the updated parameters are synchronized to the substation integrated automation system to ensure the calculation accuracy of the standardized current signal.

[0049] The beneficial effects of this invention are as follows: by adopting a two-stage ratio differential criterion combined with second harmonic braking technology, and with phase correction and balance coefficient compensation logic, the accuracy of internal transformer fault identification can be increased to over 99.9%, and the anti-maloperation rate under external faults and excitation inrush current scenarios can reach 100%, effectively solving the pain points of maloperation and missed detection in traditional protection.

[0050] The innovative parameter dynamic adjustment function can automatically optimize the second harmonic coefficient setting value and balance coefficient according to the real-time operating conditions of the transformer, taking into account both the protection sensitivity under light load and the anti-interference capability under heavy load. It is compatible with transformers of all voltage levels from 10kV to 110kV, and has a wider range of applications.

[0051] The CT disconnection detection module works in deep collaboration with the differential protection to complete disconnection identification and protection lockout within 10ms. After the fault is cleared, the protection function is automatically restored, completely avoiding false tripping accidents caused by CT disconnection and ensuring power supply continuity.

[0052] The communication module based on the DL / T634.5104 protocol realizes bidirectional full data interaction with the substation integrated automation system, supports remote adjustment of protection parameters and automatic uploading of fault recording files, and the remote adjustment parameter error is ≤±1%, which fully meets the operation and maintenance needs of unattended intelligent substations and greatly improves operation and maintenance efficiency.

[0053] The high sampling rate fault recording module can completely record the current data of the 8 cycles before the fault and the 56 cycles after the fault, generating standard COMTRADE format files, providing complete data support for fault tracing and setting optimization, and improving fault analysis efficiency by more than 80%. Attached Figure Description

[0054] Figure 1 : Transformer differential protection device structure diagram;

[0055] Figure 2 Schematic diagram of the protection interface and collaborative control principle of the transformer differential protection device. Detailed Implementation

[0056] The following embodiments illustrate the present invention in detail. All raw materials and equipment used in the present invention are commercially available products and can be directly obtained through market purchase.

[0057] The present application will be further described in detail below with reference to embodiments, comparative examples and performance test results. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0058] In the following description of the embodiments, 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 are omitted so as not to obscure the description of this application with unnecessary detail.

[0059] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0060] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0061] As used in this application specification and the appended claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if detected [the described condition or event]" may be interpreted, depending on the context, as meaning "once determined," "in response to determination," "once detected [the described condition or event]," or "in response to detection [the described condition or event]."

[0062] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0063] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0064] Example 1: Technical Explanation

[0065] Reference Appendix Figure 1-2The transformer differential protection device with second harmonic braking is connected to the BHE-300S substation integrated automation system. The system adopts a single-network mode of Ethernet (100Mbps) and consists of a ThinkServer T100C server, a BHE-358N remote communication management unit, an ES1016 switch, and two BHE-316 microcomputer line protection and control devices. The device is equipped with an independent communication module, supports the DL / T634.5104 protocol, and realizes bidirectional data interaction with the system to achieve deep coordination between protection actions and remote monitoring.

[0066] The core architecture of the device includes a current acquisition module, a data processing module, and a protection action module connected in sequence, along with a CT disconnection detection module, a fault recording module, and a communication module. The current acquisition module is equipped with three-phase current acquisition terminals on the high-voltage side (terminals A01-A06) and the low-voltage side (terminals A07-A12), with a rated input current of 5A. It acquires the secondary current signal of a 110kV Y / Δ-11 connected transformer, transmits it in real time to the data processing module via a switch, and simultaneously synchronizes it to the automation system monitoring backend. The telemetry data upload cycle is 1 second.

[0067] The data processing module first performs phase correction and balance coefficient compensation: the high-voltage side standardized current passes through... Calculations show that the normalized current on the low-voltage side passes through... Calculation, where The balance coefficient is calculated using the following formula: . The rated primary current on the high-voltage side is 630A. The rated current on the low-voltage side is 1250A. The CT ratio on the high-pressure side is 120. The CT ratio on the low-pressure side is 250, calculated as follows. This balance coefficient can be viewed remotely through the automated system backend and can be updated manually or automatically.

[0068] Calculate the differential current based on the standardized current signal. and braking current The effective values ​​of the phase currents on the high and low voltage sides are given; simultaneously, the second harmonic component of the differential current is extracted, and the proportion of the second harmonic content is calculated. Preset (Differential current setting) (Binding current setting) (Ratio braking coefficient setpoint) (Second harmonic coefficient setting), using a two-stage criterion:

[0069] when At that time, if and The fault was determined to be internal.

[0070] when At that time, if and The problem was determined to be an internal fault.

[0071] The protection action module outputs a trip signal within 0.6 seconds after detecting a fault (meeting the system's remote control response time requirements), disconnecting the corresponding switch on the transformer side. Simultaneously, it pushes fault action information, including fault type, action time, differential current, and second harmonic ratio data, to the automation system via the communication module. When the CT disconnection detection module detects a sudden current change, it locks out the protection and issues an alarm within 10ms. The alarm information is uploaded to the monitoring backend via the BHE-358N communication management unit, triggering a pop-up notification and a whistle alarm. The fault waveform recording module records the data for the 8 cycles before and 56 cycles after the fault at a sampling rate of 32 points per cycle, generating a COMTRADE format file that is automatically uploaded to the system server. It supports backend curve and table analysis, with a storage period of no less than one year.

[0072] Example 2: Internal fault protection action and system data linkage

[0073] Reference Appendix Figure 1 This embodiment is applied to a 35kV distribution transformer and connected to the BHE300S system. The device interacts with the system in real time through the communication module and supports the DL / T634.5104 protocol.

[0074] The high-voltage side has a primary rated current of 315A and a CT ratio of 60; the low-voltage side has a primary rated current of 800A and a CT ratio of 160; the balance factor is... Preset protection parameters: Protection parameters can be remotely issued from the system backend, with a modification error of ≤±1%.

[0075] During system operation, the current acquisition module collects the secondary current on the high-voltage side. Low-voltage side secondary current The data is transmitted to the data processing module via Ethernet with a transmission delay of 0.3s (meeting the requirements for analog quantity dead-zone transmission time). At the same time, it is uploaded to the monitoring backend of the automation system to display the effective value of each phase current in real time.

[0076] After the data processing module performs phase correction, the high-voltage side Low-pressure side .

[0077] The differential current of phase A was calculated. Braking current A 32-point FFT Fourier transform was performed on the differential current sampling sequence of phase A, and the effective value of the second harmonic component was calculated to be 0.72A, and the effective value of the fundamental component was 5.18A. .

[0078] because ,satisfy The problem was determined to be an internal fault.

[0079] The protection action module outputs a trip signal within 20ms, and the automation system updates the switch position status in real time. The remote signaling response time is 0.6s, and the action error is 0.04% (meeting the requirement of analog quantity comprehensive error ≤ ±1.5%). Simultaneously, the fault waveform recording module starts recording waveforms, and the generated COMTRADE format file is automatically uploaded to the system server. Maintenance personnel can view the current waveforms before, during, and after the fault through the backend, eliminating the need for on-site data export and significantly improving fault handling efficiency.

[0080] Example 3: Coordination between CT disconnection interlocking and system alarm

[0081] Reference Appendix Figure 2 This embodiment addresses a CT (current transformer) disconnection scenario in a 10kV three-winding transformer. The device is connected to the BHE300S system and is preset with... , The system is equipped with remote signaling change alarm and remote monitoring functions, and supports real-time feedback of CT disconnection status.

[0082] During normal operation, the current acquisition module acquires the secondary current on the high-voltage side. Low-voltage side secondary current The data processing module calculated that the differential current of each phase was within 0.3A. All values ​​are greater than 0.3. The system background displays "normal operation" status, the telemetry data refresh cycle is 1 second, and real-time data of high voltage side current, low voltage side current and differential current are displayed synchronously.

[0083] After 15 minutes of operation, the CT disconnection detection module detected a sudden drop in the high-voltage side A-phase current from 3.5A to 0.1A, while the high-voltage side B and C-phase currents remained at 3.4A and 3.6A respectively. No significant sudden changes in the low-voltage side phase currents were observed, immediately indicating a high-voltage side A-phase CT disconnection. The data processing module blocked the protection action module within 10ms to prevent false tripping. Simultaneously, it sent a CT disconnection alarm signal to the BHE-358N communication management unit via the communication module. The system backend received the information within 0.7s, popped up an alarm window, and issued a whistle warning. The remote signaling log displayed the "CT disconnection" event, with time stamps accurate to milliseconds (SOE resolution ≤ 5ms), facilitating maintenance personnel to trace the time of the fault.

[0084] After remotely confirming the fault location through the system backend, maintenance personnel repaired the CT disconnection on-site. Once the device detected that the current signal had returned to normal, it automatically released the interlock within 30ms, restored the differential protection function, and reported a "protection function ready" status to the automation system. The background alarm status automatically reset. The entire process did not trigger a trip, and the power supply continuity was unaffected, meeting the system's requirements for preventing misoperation.

[0085] Example 4: Linkage between Fault Recording and System Analysis

[0086] Reference Appendix Figure 1 This embodiment focuses on the collaborative function of fault recording and the BHE-300S system. The device has a sampling rate of 32 points per cycle, and the recorded data supports automatic uploading to the system server with a storage period of ≥1 year, which is suitable for the system's fault tracing and data sharing needs.

[0087] When a 110kV transformer is operating normally, the secondary current on the high-voltage side is stable at 4.2A-4.3A, and the secondary current on the low-voltage side is stable at 8.5A-8.6A. Maintaining the current above 0.25, the automation system's backend displays the current change in real time via a curve, with the curve color configured as follows. red, blue, It is green, supports scaling and historical data review, and allows maintenance personnel to remotely monitor the transformer's operating status.

[0088] When a phase-to-phase short-circuit fault occurs inside the transformer, the differential current surge reaches 1.8A, triggering the fault recording module to start. It records the three-phase current data for the 8 cycles before and 56 cycles after the fault, at 32 points per cycle. The recording file is uploaded to the system server in COMTRADE format, and the backend receives it within 1.0 second. It supports two viewing modes: table mode displays the current values ​​at each time point, while the curve mode visually presents the current surge and decay process.

[0089] Analysis data shows that: before the fault, the A-phase current on the high-voltage side was stable at 4.2A for 8 cycles; after the fault, it rose to 12.5A in the first cycle and reached a peak of 15.3A in the third cycle, with a second harmonic content... The system meets internal fault criteria, and the protection action module outputs a trip signal within 25ms. Maintenance personnel can use the historical data query function in the backend to analyze the waveform and accurately pinpoint the fault type as a short circuit between phases A and B, providing data support for maintenance and meeting the system's data processing and storage requirements.

[0090] Example 5: Coordination of Dynamic Parameter Adjustment and Remote Adjustment

[0091] Reference Appendix Figure 2 This embodiment is applied to a 20kV transformer. The device is connected to the BHE-300S system and supports remote parameter adjustment through the system background. The remote adjustment success rate is 100%, and the setting value modification error is ≤±1%, which is suitable for the unmanned operation requirements of smart substations.

[0092] Device initial preset The system monitors operating conditions in real time, including load current magnitude, inrush current frequency, and changes in CT secondary circuit parameters, and generates monthly operating condition reports. If the inrush current frequency reached 5 times in the previous month, the system automatically triggers parameter adjustment suggestions in the background. After confirmation by maintenance personnel, commands are issued via remote adjustment to adjust the parameters. The value was increased by 8% to 0.162, the remote adjustment response time was 0.7s, the execution result was fed back to the background in real time, and the setting value viewing function showed that the parameter update was successful.

[0093] Two months later, the transformer load current remained at 85% of the rated current for an extended period. The system backend again pushed a parameter adjustment prompt, and the maintenance personnel remotely adjusted the settings. The value was reduced by 6% to 0.152, the remote adjustment response time was 0.7s, and the execution result was fed back in real time to ensure protection sensitivity under light load.

[0094] Meanwhile, the system automatically checks the CT secondary circuit parameters every 30 days. In one test, it was found that the actual value of the CT transformation ratio on the low-pressure side was 198 (originally set to 200). The system then recalculated the value using the setting modification function. After authorization by maintenance personnel, the data is sent to the device data processing module to ensure the accuracy of standardized current signal calculation and keep telemetry error within 0.09%.

[0095] A minor short-circuit fault occurred inside the transformer during light-load operation, and the secondary current on the high-voltage side was collected. Low-pressure side Calculated ;

[0096] Based on the data above:

[0097] A two-stage ratio differential criterion is adopted, and the following conditions must be met: ":

[0098] when It must meet the following requirements: ;

[0099] when At that time, the following conditions must be met: .

[0100] The actual value is then calculated using the data above: .

[0101] Verification required:

[0102] First determine the range of braking current. Therefore, the second criterion applies;

[0103] Calculate the differential current threshold of the criterion: ;

[0104] Verification of differential current conditions: actual ,satisfy;

[0105] Verification of the second harmonic condition: actual The fault criteria are met, and the protection action module quickly outputs a trip signal, avoiding missed faults under light load, which reflects the full-process automated collaboration of "system monitoring - parameter adjustment - protection action".

[0106] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A transformer differential protection device for a substation integrated automation system, comprising a current acquisition module, a data processing module, a protection action module, and a communication module, wherein the current acquisition module, data processing module, and protection action module are electrically connected in sequence, and the communication module is electrically connected to the data processing module; characterized in that: The current acquisition module is equipped with a high-voltage side three-phase current acquisition terminal and a low-voltage side three-phase current acquisition terminal, which are used to acquire the secondary current signals of the high-voltage side and low-voltage side of the transformer and transmit them to the data processing module. The communication module supports the DL / T634.5104 protocol and is used to achieve bidirectional data interaction with the substation integrated automation system, including uploading telemetry data, fault information, alarm signals and waveform data to the automation system, and receiving remote control commands and protection parameters issued by the automation system. The data processing module is used for: Phase correction and balance coefficient compensation are performed on the acquired high-voltage and low-voltage secondary current signals to obtain standardized current signals; Calculating differential current based on standardized current signal and braking current ; Extract the second harmonic component from the differential current and calculate the proportion of the second harmonic content. ; Fault diagnosis is performed using a two-stage ratio differential criterion: when the braking current... Braking current setting When, if the differential current Differential current setting And the proportion of second harmonic content Second harmonic coefficient set value The fault was determined to be internal; when the braking current... Braking current setting At that time, if And the proportion of second harmonic content The fault was determined to be internal; among them Set the ratio braking coefficient to a fixed value; The protection action module is used to output a trip signal and disconnect the switch on the corresponding side of the transformer when the data processing module determines that there is an internal fault.

2. The transformer differential protection device for a substation integrated automation system according to claim 1, characterized in that, The differential current setpoint The setting range is 0.10A-10.00A, and the braking current setting value is... Its setting range is 0.10A-10.00A, and it is compatible with current transformers with a rated input current of 5A / 1A; the ratio braking coefficient setting value is... The setting range is 0.30-0.70, and the second harmonic coefficient is set to... The setting range is 0.10-0.40, suitable for power transformers with voltage levels of 10kV-110kV; among which, the differential current setting value... The braking current setting is configured to avoid the maximum unbalanced current under the transformer's rated load. Set the transformer to 0.5-1 times its rated secondary current.

3. The transformer differential protection device for a substation integrated automation system according to claim 1, characterized in that, It also includes a CT disconnection detection module, which is electrically connected to the data processing module, and the CT disconnection determination logic is executed before the differential fault determination criterion. The CT disconnection detection module is used to detect the abrupt change characteristics of the current signal on the high-voltage side or the low-voltage side: when the current value of a certain phase on a certain side drops by ≥90% within 2 consecutive sampling cycles and drops to less than 5% of the rated current, while the current of other phases on this side and any phase current on the opposite side does not change by more than ±5%, it is determined that the CT is disconnected. The data processing module blocks the trip output of the protection action module within 10ms after determining the CT disconnection, and pushes a time-stamped CT disconnection alarm signal to the substation integrated automation system through the communication module. When the disconnected phase current is detected to recover to more than 90% of the normal operating value, and there are no abnormalities for 3 consecutive sampling cycles, it is determined that the CT disconnection fault is cleared, the differential protection function is automatically restored, and the status is fed back to the automation system.

4. The transformer differential protection device for a substation integrated automation system according to claim 1, characterized in that, The phase correction is applicable to For transformers with different wiring configurations, the standardized current signal on the high-voltage side passes through... The calculation yielded, where , , The high-voltage side three-phase secondary current sampling values; the low-voltage side standardized current signal is passed through... The calculation yielded, where , , These are the sampled values ​​of the three-phase secondary current on the low-voltage side; in This is the low-pressure side balance coefficient. These are the primary rated currents for the high and low voltage sides, respectively. The phase correction is performed based on the synchronous sampling data of the high and low voltage side CTs, respectively, with a sampling synchronization error ≤10μs.

5. The transformer differential protection device for a substation integrated automation system according to claim 1, characterized in that, The differential current The braking current ;in This is the effective value of the phase current of the standardized current signal on the high-voltage side. This is the effective value of the phase current of the standardized current signal on the low-voltage side.

6. The transformer differential protection device for a substation integrated automation system according to claim 1, characterized in that, It also includes a fault recording module, which is electrically connected to the data processing module. This module is used to handle situations where the differential current surge exceeds a setpoint. The differential current surge is the absolute value of the difference between the current differential current at the current moment and the differential current in the previous sampling period. The setpoint is adjusted to the differential current setpoint. 0.5 times that of the CT disconnection determination period, the locked waveform recording is initiated; The three-phase current sampling data is recorded at a sampling rate of 32 points per cycle for the 8 cycles before the fault and the 56 cycles after the fault. A COMTRADE format waveform file is generated within 5 seconds after the waveform recording is completed, and uploaded to the substation integrated automation system server through the communication module, supporting the background viewing and analysis of the automation system.

7. The transformer differential protection device for a substation integrated automation system according to claim 1, characterized in that, The telemetry data uploaded by the communication module includes the RMS values ​​of the high-voltage side and low-voltage side currents, differential current, braking current, and the percentage of second harmonic content. The default upload cycle is 1 second, which is adaptively matched with the data refresh cycle of the substation integrated automation system. Telemetry data can be transmitted across dead zones, with the dead zone value set to 0.2% of the rated value; the communication module receives parameters from the automation system, including differential current settings. Braking current setting value Ratio braking coefficient set value and the second harmonic coefficient set value Parameter modification error .

8. A transformer differential protection method for a substation integrated automation system, comprising core steps of current acquisition, data processing, and protection action; characterized in that, The method includes the following steps: Step 1: Acquire the three-phase secondary current signals of the high-voltage side and low-voltage side of the transformer through the current acquisition module and transmit them to the data processing module; Step 2: The data processing module performs phase correction and balance coefficient compensation on the high-voltage and low-voltage secondary current signals respectively to obtain standardized current signals; wherein, the phase correction is for the Y / Δ11 connected transformer, and the high-voltage side standardized current signal is obtained through... Calculation, where , , The high-voltage side three-phase secondary current sampling values; the low-voltage side standardized current signal is passed through... Calculation, where , , These are the sampled values ​​of the three-phase secondary current on the low-voltage side; This is the low-pressure side balance coefficient. These are the primary rated currents for the high and low voltage sides, respectively. These are the CT ratios for the high- and low-pressure sides, respectively. Step 3: Calculate the differential current based on the standardized current signal and braking current ,in This is the effective value of the phase current on the high-voltage side. This represents the effective value of the phase current on the low-voltage side. Step 4: Extract the second harmonic component from the differential current and calculate the proportion of the second harmonic content. The It is the ratio of the effective value of the second harmonic component to the effective value of the fundamental component; and it calls the preset differential current setting. Braking current setting value Ratio braking coefficient set value and the second harmonic coefficient set value ; Step 5: Use a two-stage ratio differential criterion to determine the fault type: when At that time, if and It was determined to be an internal fault; when At that time, if and The fault was determined to be internal. Step 6: If the fault is determined to be internal, the protection action module outputs a trip signal to disconnect the corresponding switch on the transformer side; if the fault is not determined to be internal, return to step 1 for continued monitoring.

9. A transformer differential protection method for a substation integrated automation system according to claim 8, characterized in that, It also includes a CT disconnection collaborative protection step, and the CT disconnection determination logic takes precedence over the differential fault determination criterion in step 5, specifically: While acquiring the current signal in step 1, the CT disconnection detection module monitors the abrupt change characteristics of the current signals of each phase on the high-voltage side and the low-voltage side in real time. When a sudden drop of ≥90% in the current value of a certain phase on a certain side is detected within two consecutive sampling cycles, and the drop is less than 5% of the rated current, while the current of other phases on this side and any phase current on the opposite side does not change by more than ±5%, it is determined that the CT is disconnected. The data processing module immediately blocks the trip output of the protection action module and generates a time-stamped CT disconnection alarm signal, which is then uploaded to the substation integrated automation system via the communication module. When the current of the disconnected phase is detected to recover to more than 90% of the normal operating value, and there are no abnormalities for three consecutive sampling cycles, it is determined that the CT disconnection fault has been resolved, the differential protection function is automatically restored, and the status is fed back to the automation system.

10. A transformer differential protection method for a substation integrated automation system according to claim 8, characterized in that, It also includes a step for dynamic parameter adjustment: Real-time monitoring of transformer operating conditions, including load current magnitude, frequency of inrush current occurrence, and changes in CT secondary circuit parameters, with monitoring data synchronously uploaded to the substation integrated automation system; When the load current remains above 80% of the rated current for 72 consecutive hours, the second harmonic coefficient should be set within the setting range. Reduce by 5%~10%; when the frequency of inrush current exceeds 3 times per month within a statistical period of 1 month, the second harmonic coefficient will be set within the adjustment range. Increase by 5%~10%; the inrush current determination criteria are as follows: Furthermore, the differential current has not reached the operating setpoint; the upper and lower limits of parameter adjustment shall not exceed the setting range defined in claim 2; Based on the changes in the CT secondary circuit parameters, the balance coefficient is recalculated. After verification, the data is updated to the data processing module, and the updated parameters are simultaneously synchronized to the substation integrated automation system.

Images