Intelligent current transformer open circuit prevention protection device suitable for power distribution automation DTU transformation

Abstract

The invention relates to an intelligent current transformer open circuit prevention protection device suitable for power distribution automation DTU transformation. The intelligent current transformer open circuit prevention protection device comprises a device shell, a PCB arranged in the device shell and a composite short circuit module integrated on the PCB. Four positive electrode external wiring ports are formed in the upper end of the device shell, and four negative electrode external wiring ports are formed in the other side of the device shell and correspond to an A phase, a B phase, a C phase and a grounding phase of an alternating current secondary circuit of a DTU respectively; the primary side of the PCB is provided with four positive electrode internal wiring ports, and the other side of the PCB is provided with four negative electrode internal wiring ports. The four positive electrode internal wiring ports are connected with the four positive electrode external wiring ports one by one through leads, and the four negative electrode internal wiring ports are connected with the four negative electrode external wiring ports one by one through leads, so that a short-circuit loop for respectively controlling an A phase, a B phase, a C phase and a grounding phase of an alternating-current secondary loop of the DTU is formed; and open-circuit control is realized through the composite short-circuit module. According to the invention, embedded installation is realized, and the cost and difficulty of power distribution automation reconstruction are reduced.

Description

Technical Field

[0001] This invention belongs to the technical field of power system distribution automation and relay protection equipment, and particularly relates to an intelligent current transformer anti-open circuit protection device suitable for the transformation of distribution automation DTU. Background Technology

[0002] In distribution automation upgrades, the Distribution Terminal Unit (DTU) is the core equipment for realizing "telemetry, telesignaling, and remote control" of the distribution network. It collects primary-side current signals through current transformers (CTs) to achieve fault diagnosis, load monitoring, and remote control, serving as the "nerve endings" of the intelligent operation of the distribution network. As a key component of the DTU, the CT's secondary side needs to be maintained in a near-short-circuit state (output voltage ≤10V) during normal operation. However, during DTU upgrades, the risk of an open circuit on the CT's secondary side increases significantly. Once an open circuit occurs, it will have a devastating impact on the DTU upgrade project and the distribution system. Firstly, it can directly damage the core DTU module, leading to upgrade failure. DTU upgrades require wiring adjustments to the CT's secondary circuit. If improper operation causes an open circuit on the CT's secondary side, a high voltage of 3000V-15000V will be generated instantaneously, damaging components such as the ADC chip and precision resistors of the acquisition module, causing the DTU's acquisition function to completely fail. Secondly, burning out the CT equipment can cause power grid outages. When the secondary side of the CT is open-circuited, all the primary current is converted into excitation current, leading to severe saturation of the CT core and a sudden temperature rise. This can burn out the insulation layer of the CT winding, causing permanent damage to the CT. After the CT is damaged, the DTU loses its current acquisition signal and cannot monitor the load and faults of the power grid. Power outages are required to replace the CT (power outage time ≥ 4 hours), directly affecting the power supply to residential and industrial users and causing serious power supply reliability accidents. Thirdly, it endangers the personal safety of on-site construction personnel. DTU upgrades are often carried out in a live or semi-live state (to reduce the impact of power outages). The thousands of volts of high voltage generated by the open circuit of the CT secondary side can form a high-voltage electric field through the terminals and exposed wires, which can easily cause arc discharge, resulting in electric shock injuries or deaths to construction personnel. At the same time, the CT casing burned out by the high temperature may explode, creating a secondary safety hazard and seriously threatening the lives of personnel at the upgrade site.

[0003] However, the various anti-open circuit devices currently on the market have significant technical defects in DTU retrofit scenarios, namely insufficient size compatibility: traditional devices are generally larger than 120mm×100mm, while DTU cabinets are 19-inch standard cabinets with small internal space (single module installation space ≤100mm×80mm), making it difficult to embed and install them. Additional expansion of the DTU cabinet is required, increasing the cost and difficulty of retrofit. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes an intelligent current transformer anti-open-circuit protection device suitable for power distribution automation DTU retrofitting. This device enables embedded installation, reduces the cost and difficulty of power distribution automation retrofitting, ensures the safety of retrofitting operations, and avoids damage to components.

[0005] The above-mentioned objective of this invention is achieved through the following technical solution: An intelligent current transformer open-circuit protection device suitable for the retrofitting of distribution automation DTUs includes a device housing, a PCB circuit board disposed within the device housing, and a composite short-circuit module integrated on the PCB circuit board. The device housing is a miniaturized housing with dimensions of 92mm × 41.2mm × 33mm. Four positive external connection ports are provided on one side of the upper part of the device housing, and four negative external connection ports are provided on the other side, corresponding to phases A, B, C, and ground of the AC secondary circuit of the distribution terminal unit (DTU), respectively. Four positive internal connection ports are provided on the primary side of the PCB circuit board, and four negative internal connection ports are provided on the other side. The four positive internal connection ports are connected to the four positive external connection ports one by one via leads, and the four negative internal connection ports are connected to the four negative external connection ports one by one via leads, forming short-circuit loops that control phases A, B, C, and ground of the AC secondary circuit of the distribution terminal unit (DTU) respectively. The composite short-circuit module achieves circuit breaking control.

[0006] Furthermore, the composite short-circuit module includes a BT139 bidirectional thyristor, a 100pF low-capacitance varistor, and silver alloy contacts.

[0007] Furthermore, the composite short-circuit module has a conduction voltage threshold of 33V, a conduction current ≥50A, a reset voltage threshold of 25V, and a conduction time ≤20ms.

[0008] Furthermore, the device housing is made of flame-retardant ABS material with a flame-retardant rating of V0, and the surface of the device housing is provided with heat dissipation holes, and its protection level reaches IP30.

[0009] Furthermore, by installing small relay switches on the external lines between LAS1 and LAS2, between LBS1 and LBS2, between LCS1 and LCS2, and between LS1 and LS2, and embedding corresponding overvoltage sensors in each of the PCB circuit boards, when an overvoltage signal is collected, a command is sent to the corresponding switch to short-circuit the secondary side.

[0010] The advantages and positive effects of this invention are as follows: 1. This invention completely avoids the risk of damage to CT open-circuit equipment: ≤20ms high-speed protection response, can complete the short circuit before the CT open-circuit high voltage impacts the DTU, the damage rate of the DTU acquisition module is reduced from 85% to 0, the CT burn-out rate is reduced from 100% to 0, and the modification and maintenance costs are greatly reduced.

[0011] 2. This invention ensures the personal safety of personnel during DTU retrofit construction: the instantaneous short-circuit high voltage when the CT is open eliminates the risk of arc discharge and high-voltage electric shock, reducing the accident rate of personnel at the retrofit site to 0; 3. This invention reduces the cost and difficulty of modification: The miniaturized design eliminates the need to modify the DTU cabinet, allowing for direct integrated installation, reducing the cost of single-site modification by 30% and shortening the modification period by 20%. Attached Figure Description

[0012] Figure 1 This is a physical appearance drawing of the intelligent current transformer anti-open circuit protection device of the present invention; Figure 2 This is a schematic diagram of the appearance of the intelligent current transformer anti-open circuit protection device of the present invention; Figure 3 These are dimensional drawings of the intelligent current transformer anti-open circuit protection device of the present invention: 3a, front view; 3b, top view; 3c, left view. Figure 4 This is an internal wiring diagram of the intelligent current transformer open-circuit protection device of the present invention; Figure 5 This is a circuit diagram of the composite short-circuit module of the current transformer open-circuit protection device of the present invention. Detailed Implementation

[0013] The structure of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that these embodiments are descriptive and not limiting.

[0014] An intelligent open-circuit protection device for current transformers suitable for DTU retrofitting in power distribution automation is available. Please participate. Figures 1-5The invention comprises a device housing, a PCB circuit board disposed within the device housing, and a composite short-circuit module integrated on the PCB circuit board. The device housing is a miniaturized housing with dimensions of 92mm × 41.2mm × 33mm, suitable for installation in a 19-inch DTU standard cabinet. The device housing is made of flame-retardant ABS material with a flame-retardant rating of V0. The surface of the device housing has heat dissipation holes, achieving an IP30 protection rating and supporting DIN rail quick installation. The upper part of the device housing has four positive external connection ports, and the other side has four negative external connection ports, corresponding to phase A, phase B, phase C, and the ground phase of the AC secondary circuit of the power distribution terminal unit (DTU), respectively. The primary side of the PCB circuit board has four positive internal connection ports: LAS1, LBS1, LCS1, and LS1, and the other side has four negative internal connection ports: LAS2, LBS2, LCS2, and LS2. The four positive internal wiring ports are connected to the four positive external wiring ports one by one through leads, and the four negative internal wiring ports are connected to the four negative external wiring ports one by one through leads, forming short-circuit loops that control the A phase, B phase, C phase and ground phase of the AC secondary circuit of the power distribution terminal unit (DTU) respectively. The circuit breaking control is achieved through the composite short-circuit module.

[0015] The composite short-circuit module consists of a BT139 bidirectional thyristor, a 100pF low-capacitance varistor, and silver alloy contacts. It has a conduction current ≥50A and a leakage current <2mA to avoid interfering with the DTU current acquisition accuracy.

[0016] By installing small relay switches on the external lines between LAS1 and LAS2, LBS1 and LBS2, LCS1 and LCS2, and LS1 and LS2, and embedding corresponding overvoltage sensors on the PCB circuit board for each, a command is sent to the corresponding switch upon detecting an overvoltage signal, thereby short-circuiting the secondary side. The core principle of the CT open-circuit protection device lies in CT overvoltage protection, mainly used to prevent damage to the device or threats to personal safety caused by open-circuit current on the secondary side and abnormal high voltage on the primary side. In use, the device is connected in parallel across both sides of the CT secondary circuit. Once an overvoltage signal is detected, the device will conduct the CT on the secondary side, bringing the resistance close to zero, thereby reducing the voltage.

[0017] When the AC secondary circuit of the distribution terminal unit (DTU) is open-circuited or an abnormal overcurrent occurs in the primary winding, the voltage generated in the secondary winding is much higher than the normal operating voltage (the value depends on the CT's parameters and operating conditions). At this time, the parallel-connected protection device instantly enters the conducting state, thereby effectively preventing damage to meters caused by the secondary overvoltage of the transformer and posing a safety hazard to operators. The open-circuit protection device of this invention can reliably short-circuit the secondary winding within 20ms of the overvoltage.

[0018] The usage of this intelligent current transformer open-circuit protection device is as follows: First, device adaptation and installation integration: parameter adaptation: through remote command issuance from DTU, the protection device's on-state voltage threshold is set to 33V and the reset voltage threshold is set to 25V, adapting to the CT secondary side voltage characteristics; Secondly, physical installation: The device (92mm×41.2mm×33mm) is installed next to the terminal block inside the DTU cabinet using a 35mm standard guide rail, occupying only 0.00019m of space. 3 No expansion or modification of the DTU cabinet is required.

[0019] Third, the renovation and construction test: During the wiring process, a simulated open circuit on the secondary side of the CT was created (by disconnecting one secondary wire). The voltage on the secondary side of the CT instantly rose to 37V. The protection device conducted a short circuit within 15ms, and the DTU acquisition module was not subjected to any impact. At the same time, the DTU received a "CT open circuit fault" signal, triggered an audible and visual alarm and uploaded it to the dispatch center. The renovation and construction personnel immediately stopped the operation, thus avoiding damage to the DTU module.

[0020] Fourth, operational fault simulation: After the modification is completed, the CT secondary side is open during simulated operation, the voltage rises to 35V, and the device completes the protection action within 18ms; when the temperature control module monitors the temperature rises to 83℃, it automatically adjusts the current and the temperature stabilizes at 81℃; the operation and maintenance personnel issue a "remote reset" command through the dispatch center, and the device resets within 450ms, and the DTU resumes normal data acquisition. The whole process does not require on-site intervention.

[0021] Fifth, the effectiveness of the transformation was verified, and no abnormalities were found throughout the entire verification process.

[0022] Although embodiments and drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. An intelligent current transformer open-circuit protection device suitable for the retrofitting of distribution automation DTUs, characterized in that: The device includes a housing, a PCB circuit board housed within the housing, and a composite short-circuit module integrated on the PCB circuit board. The housing is a miniaturized housing with dimensions of 92mm × 41.2mm × 33mm. Four positive external connection ports are located on the upper part of the housing, and four negative external connection ports are located on the other side, corresponding to phases A, B, C, and ground of the AC secondary circuit of the power distribution terminal unit (DTU), respectively. Four positive internal connection ports (LAS1, LBS1, LCS1, and LS1) are located on the primary side of the PCB circuit, and four negative internal connection ports (LAS2, LBS2, LCS2, and LS2) are located on the other side. The four positive internal connection ports are connected to the four positive external connection ports one by one via leads, and the four negative internal connection ports are connected to the four negative external connection ports one by one via leads, forming short-circuit loops that control phases A, B, C, and ground of the AC secondary circuit of the DTU, respectively. The composite short-circuit module achieves circuit breaking control.

2. The intelligent current transformer open-circuit protection device for power distribution automation DTU retrofitting according to claim 1, characterized in that: The composite short-circuit module includes a BT139 bidirectional thyristor, a 100pF low-capacitance varistor, and silver alloy contacts.

3. The intelligent current transformer open-circuit protection device for DTU retrofitting in power distribution automation according to claim 1, characterized in that: The composite short-circuit module has a conduction voltage threshold of 33V, a conduction current ≥50A, a reset voltage threshold of 25V, and a conduction time ≤20ms.

4. The intelligent current transformer open-circuit protection device for power distribution automation DTU retrofitting according to claim 1, characterized in that: The device housing is made of flame-retardant ABS material with a flame-retardant rating of V0. The surface of the device housing is provided with heat dissipation holes, and its protection level reaches IP30.

5. The intelligent current transformer open-circuit protection device for DTU retrofitting in power distribution automation according to claim 1, characterized in that: By installing small relay switches on the external lines between LAS1 and LAS2, between LBS1 and LBS2, between LCS1 and LCS2, and between LS1 and LS2, and embedding corresponding overvoltage sensors on the PCB circuit board, when an overvoltage signal is collected, a command is sent to the corresponding switch to short-circuit the secondary side.

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