Brief Analysis Of Digital Primary And Secondary Integrated Pole-mounted Circuit Breakers And Their Engineering Applications
With the continuous development and upgrading of primary and secondary integrated distribution switch technology, domestic primary and secondary Lv Pole Mounted Circuit Breakers has also ushered in a wide range of engineering applications. This paper discusses the technical solutions of typical digital pole-mounted circuit breakers, including specific equipment technical routes, structural composition, digital module technical requirements, etc., carries out equipment reliability analysis and engineering application analysis, and highlights the application advantages of digital pole-mounted circuit breakers compared with traditional electromagnetic or electronic pole-mounted circuit breakers. It has a certain guiding role in the engineering application of digital pole-mounted switch circuit breakers.
Introduction
Under the background of the country's promotion of carbon peak and carbon neutrality, building a new power system with new energy as the main body has become an important development trend, and digital power grid will become a new form of carrying new power systems. At present, the construction of digital power grids has entered a period of rapid development, and the construction of digital distribution networks has also become an important part of it. As an important switchgear for overhead lines of domestic distribution networks, pole switches are equipment for overhead line distribution automation, and digital pole switches have also become the core equipment of digital distribution networks. This article introduces the technical solution of digital pole-mounted switches, discusses its technical route, structural composition and technical requirements of ADMU, conducts equipment reliability analysis and engineering application analysis, and summarizes the engineering application characteristics of digital pole-mounted switches.
1 Technical solution of digital pole-mounted switches
1.1 Technical route
Compared with traditional electromagnetic or electronic switches, digital switches mainly realize the local digitization of switch analog quantities, and then transmit them to the terminal unit in the form of digital quantities to complete signal processing. At present, there are two main technical routes for completing the local digitization of analog quantities. The first is that the current sensor uses a Rogowski coil to convert the primary current into a secondary small signal and then convert it into a digital quantity through an integrator, while the voltage sensor converts the secondary small voltage signal into a digital quantity through an analog-to-digital (AD) converter; the second is to input the secondary analog small signal of the traditional electronic voltage and current sensor on the switch body into the ADMU module nearby, complete the analog-to-digital conversion of the signal through the ADMU, and then transmit the digital signal to the terminal unit through the primary and secondary connection cables, and the terminal unit realizes the power supply of ADMU through the primary and secondary connection cables. At present, due to the fact that the Rogowski coil technology in the first solution is not mature enough in the application of distribution network switches, the equipment is large in size, and the sensing accuracy is relatively low, it cannot be expanded in the pole-mounted circuit breaker. Therefore, the digital pole-mounted switch mainly adopts the second technical route.
1.2 Structural composition
At present, the mainstream digital pole-mounted switch in China is a spring-operated digital circuit breaker, which adopts a spring operating mechanism, a three-phase discrete solid-sealed pole structure, and an external voltage and current sensor or a deep fusion solid-sealed pole to complete the sensing of voltage and current analog small signals. The digital (ADMU) module is integrated in the switch box through a built-in or external way to complete the local digitization of the voltage and current analog small signals, and then the signal transmission between the primary and secondary devices is completed through the twisted pair shielded cable through the 485 communication method. Therefore, the digital pole-mounted switch is mainly composed of a switch body with an integrated digital (ADMU) module, a digital terminal unit, and a primary and secondary connection cable.
1.3 Key technical requirements for digitization
The pole-mounted switch realizes on-site digitization of analog quantity by integrating ADMU. However, ADMU is an active electronic device, and its service life is difficult to match the service life of the switch body. Therefore, the core board of the ADMU module is required to be hot-swappable and replaceable online. Therefore, the hot-swappable structural design, input and output interface protection design, and digital signal transmission anti-interference design of the ADMU module have become the key technical requirements for the reliable application of the ADMU module.
(1) Hot-swappable structural design: The ADMU module should include a shell and a core board. The shell is connected to the switch box to complete the interface conversion between the analog signal of the internal sensor of the switch and the external core board; and the core board and the shell have an online plug-in and unplug function. The board is automatically locked after being inserted into the shell, and can be unbuckled and pulled out by the tool knob, realizing the function of online plug-in and replacement of the module board after failure.
(2) Interface protection design: There are two interfaces in the ADMU module application: one is the connection interface between the shell and the box, which needs to meet the IP65 protection requirements to prevent water vapor from entering the switch box, causing rust on the internal mechanism and electrical short circuit of the interface; the other is the electrical interface between the shell and the core board, which needs to meet at least the IP55 protection requirements. When used in outdoor environments, it should be ensured that water vapor cannot enter the interface to avoid oxidation or short circuit of the interface pins.
(3) Anti-interference design of digital signal transmission: After the ADMU module completes the local digitization of the analog quantity, it transmits it to the terminal through a 485 digital signal. The digital signal transmission is easily affected by the electromagnetic environment. Therefore, a twisted pair shielded cable is required for digital signal transmission from the core board to the terminal unit. The cable shielding layer is single-point grounded to reliably shield external electromagnetic interference; at the same time, it is necessary to reasonably select the 485 communication chip to ensure the stability of signal transmission and reception.
2 Reliability analysis of digital pole switches
Compared with traditional electromagnetic or electronic pole switches, the main difference of digital pole switches is that they have an external integrated ADMU module, and the primary and secondary devices transmit telesignaling and telemetry signals through digital signals. Traditional electromagnetic or electronic pole switches are passive devices and have been widely used in the market with high application reliability. After the digital pole-mounted switch introduces active ADMU module devices, it brings risks to the application reliability of the switch. The main influencing factors are:
(1) The switch box adds ADMU module installation holes and increases the box sealing structure;
(2) The sensor secondary circuit adds connection interfaces, which increases the risk of secondary wiring errors;
(3) The ADMU module requires online hot-swappable design, which increases the external interface protection and connection reliability requirements;
(4) The ADMU module is an active device, and its service life cannot match the service life of traditional pole-mounted switch passive devices. It is necessary to improve the reliability of module components and combine online replacement of modules to improve the service life of the switch;
(5) The ADMU module transmits digital signals through 485 signals, which increases the anti-interference design of digital signal transmission.
In summary, to improve the application reliability of digital pole-mounted switches, it is necessary to focus on ensuring the optimal selection of ADMU module components, improving the application stability and service life of the module, and secondly, ensuring the sealing and connection reliability of each module interface through structural optimization design.
3 Engineering application analysis based on digital pole-mounted switches
The engineering application of digital pole-mounted switches brings some application advantages, such as:
(1) The voltage and current telemetry sensing accuracy is higher, which can usually meet the 0.5-level complete equipment sensing accuracy, which is better than the 1-level accuracy of traditional pole-mounted switches;
(2) Based on high-precision telemetry sensing, more accurate line fault identification and isolation can be achieved, and the stability of line power supply can be improved;
(3) The telemetry cables between primary and secondary equipment are reduced, and only one 10-core remote control cable is retained to meet the three-remote signal transmission of the complete equipment;
(4) Without increasing the number of switch plugs, the switch telemetry and telesignaling signal expansion can be met, and the three-phase voltage, zero-sequence voltage, three-phase measurement and protection current, zero-sequence measurement and protection current on the power supply side and the load side can be collected in real time. It can meet the remote signaling signal collection of open position, closed position, unstored energy position, low pressure, etc., and even in the future, the remote signaling signal transmission such as switch temperature monitoring and partial discharge monitoring can be expanded. It is flexible in application and can adapt to more protection application modes.
(5) In the process of small signal transmission, analog transmission is easily interfered by environmental factors of the transmission circuit, while digital transmission largely avoids the interference of environmental factors and is not affected by the load of the transmission circuit, which has obvious advantages of lossless signal transmission.
Digital pole switches are innovative products that have transformed from primary and secondary pole switches to digital switches in the past two years. Through the large-scale engineering application of digital pole switches, power distribution line power monitoring can be achieved more accurately, line fault identification and isolation can be achieved more accurately, and the status monitoring of switch equipment can be achieved more comprehensively.
4 Conclusion
This paper briefly analyzes the current technical solutions of digital pole switches, focusing on the analysis of key digital technical requirements, and discusses the factors affecting the application reliability of digital pole switches. At the same time, it also analyzes the advantages of digital switch engineering applications, which plays a certain guiding role in the product design and engineering application of digital pole switches.
