Tina Li

Jiangsu Acrel Electrical Manufacturing Co.LTD.   Wuxi Jiangsu  214405

Abstract: With the increasing demand for electricity, power supply reliability requirements of the power system is becoming higher and higher, many power supply systems have two or more power supply lines. Automatic switching device for backup power supply can effectively improve the reliability of power supply, this type of device can automatically and quickly put the backup power supply into operation or switch the user to the backup power supply after the working power supply is disconnected due to a fault. This paper introduces AM5-DB low-voltage automatic switching device for backup power supply, which can provide corresponding protection functions for different power supply modes in Dongting substation project, and can greatly improve the reliability, safety and power supply quality of substation operation, which is conducive to the realization of comprehensive automation of the substation, and the realization of unmanned or fewer people on duty.

Keywords: Reliability; automatic switching of backup power supply; low-voltage automatic switching device for backup power supply

1 Project Overview

This project is the new construction of Hunan Dongting 500kV substation, the main content of the project is the substation low-voltage distribution cabinet, including three station transformer inlet and one contact, of which the voltage level of 0# station transformer is 10kV/0.4kV, and the voltage level of 1# and 2# station transformers is 35kV/0.4kV.When any station transformer is withdrawn, the backup station transformer should be able to automatically switch to the de-energized work busbar section to continue power supply. And when the low-voltage working busbar of the station is equipped with equipment self switching devices, it should have the function of low-voltage busbar fault blocking backup self switching.

The low-voltage backup automatic switching device for this project is provided by Acrel Electric, and Hebei Guanyi Rongxin Technology Co., Ltd. is responsible for construction and operation maintenance. Hebei Guanyi Rongxin Technology Co., Ltd. is a comprehensive energy technology service enterprise, which is committed to the research and development, production and sales of energy-saving equipment for intelligent server room, intelligent battery management system, energy storage system, smart grid products, development, investment, construction and operation service of new energy projects, general contracting service of electric power engineering projects, and operation and maintenance service of electric power, etc. The company consists of marketing center, R&D center, design center, production center, engineering center, operation center, financial center, comprehensive center, has a perfect management system, and constantly innovate to improve the competitiveness of enterprises. The company has achieved rapid, stable, and healthy development through technological progress, scientific management, and excellent service.

2 Product Demand

The main electrical wiring diagram for this project is shown in Figure 1, and a total of the following two methods of self-provisioning logic need to be implemented:

Fig.1 Electrical main wiring diagram

Control method 1: # 0 and # 2 stations are put into operation, while # 1 station is not put into operation.

（1）During normal operation, 2QF is closed, 5QF is closed, 3QF, 4QF is disconnected, at this time, #2 station transformer operates with two sections of busbar  (#1 station for emergency power, manual operation, 1QF default disconnection). When the automatic switching device for backup power supply detects the voltage, current and circuit breaker status at this time, after a certain delay, the backup self charging enters preparation state.

（2）When the voltage of the incoming line of the #2 station transformer is abnormal and the backup automatic switch detects that there is no voltage or current in the #2 station transformer, the incoming circuit breaker 2QF and the busbar circuit breaker 5QF of the #2 station transformer will be disconnected. Then, the backup automatic switch will close the circuit breakers 3QF and 4QF of the #0 station transformer. At this time, the #0 station transformer will bring two sections of busbar.

（3）When the incoming voltage of #2 station transformer returns to normal and the automatic switching device for backup power supply detects the voltage of incoming line 2, the device is ready to charge and resume power supply from the #2 incoming line. After the charging is completed, the device will disconnect the QF3 and QF4 switches of the #0 station transformer circuit breaker, close the 2QF incoming circuit breaker and 5QF busbar circuit breaker of the #2 station transformer, and restore the entire section of the # 2 station.

Control method 2: #1, #0, and #2 stations are put into operation.

（1）During normal operation: #1 station transformer incoming line with section I busbar, #2 station transformer incoming line with section II busbar, that is 1QF, 2QF are connected, 3QF, 4QF, 5QF are disconnected. When the backup automatic switching device detects the voltage, current and circuit breaker status at this time, after a certain delay, backup self charging enters preparation state.

（2）The incoming line 1 voltage is abnormal and then returns to normal:

① When the voltage of the 1QF incoming line is abnormal and the automatic switching device for backup power supply detects that the # 1 station transformer has no voltage or current, the 1QF incoming line switch is disconnected, and then the 3QF switch of the # 0 station transformer is closed to supply power to the section I busbar from the # 0 station transformer. (Among them, the 5QF busbar switch serves as a manual maintenance switch).

② When the automatic switching device for backup power supply detects that the incoming line 1 has returned to normal voltage, the backup power switch is ready to resume charging from the #1 incoming line. After charging is completed, disconnect the 3QF switch from the backup automatic switch, close the 1QF, and restore the I section busbar of the #1 station transformer.

（3）The incoming line 2 voltage is abnormal and then returns to normal:

① When the voltage of the 2QF incoming line is abnormal and the automatic switching device for backup power supply detects that the # 2 station transformer has no voltage or current, the 2QF incoming line switch is disconnected, and then the 4QF switch of the #0 station transformer is closed to supply power to the section II busbar from the #0 station transformer. (Among them, the 5QF busbar switch serves as a manual maintenance switch).

② When the automatic switching device for backup power supply detects that the incoming line 2 has returned to normal voltage, the backup power switch is ready to resume charging from the incoming line # 2. After charging is completed, disconnect 4QF from the backup automatic switch, close 2QF, and restore the II section busbar of the # 2 station transformer.

3 Product Solutions

There are a total of 3 station transformer incoming lines, 1 busbar, using a single busbar system, equipped with 2 AM5-DB low-voltage automatic switching protection device for backup power supply installed on the 3QF and 4QF cabinets for use. A secondary schematic diagram with interlocking relationship is drawn according to the power supply mode, and a special program is customized to achieve mutual switching of the main and backup power supplies,

The design scheme for the back terminal of the device is as follows:

Fig. 2 Back terminal diagram of 2 AM5-DB low-voltage automatic switching device for backup power supply

4 On-site installation pictures

The AM5-DB low-voltage automatic switching protection device for backup power supply of this project is installed on the low-voltage switchgear in local decentralized manner, and the site installation is shown in the following figure, the project has been put into use since 2023 and is running normally.

Fig.3 Installation picture of AM5-DB low-voltage automatic switching protection device for backup power supply

5 Conclusion

The power supply in China mainly relies on the State Grid, and the power gap is constantly increasing, especially during peak electricity consumption periods when power shortages are severe. Therefore, many large enterprises have built their own power plants or equipped generators. The automatic switching device for backup power supply can ensure uninterrupted power supply and improve high reliability of power supply, and has become an important part of protection and control circuits in modern distribution engineering. The distribution project of Dongting 500kV substation introduced in this article uses AM5-DB low-voltage automatic switching protection device for backup power supply to provide corresponding protection functions for different power supply methods. Not only has it improved the reliability of power supply, achieved comprehensive automation of the entire distribution project, but it has also effectively reduced the labor intensity of workers.

References:

[1] Acrel Enterprise Microgrid Design and Application Manual. Version 2020.6

[2] Acrel 35KV and the following substation intelligent power distribution system design and product secondary principle atlas.Version 2020.October

[3] Acrel Subscriber Substation Integrated Automation and Operation and Maintenance Solution.Version 2021.November