Design Of Arc Protection System Based On DSP And Its Engineering Application To LV/MV Switchgear

In recent years, with the rapid development of economy, the domestic power industry is constantly developing, LV/MV switchgear is increasingly used in the transmission and distribution systems. At the same time, when short circuit fault occurs in LV/MV switchgear, generated arc will do a lot of harm to equipment and personnel, even evolve into a busbar accident, and cause a great economic losses. For busbar with35kV voltage class or lower, there are no special protective devices at present, relies on backup overcurrent protection of previous level element in most cases, but it often needs a long time to remove fault, suffers great losses. Therefore, it is urgent to install arc protection system in LV/MV switchgear.This topic orginates from "arc protection sytem" development project of one electric limited company in Shandong Province. This system uses the principle of double criterion detecting both arc and overcurrent, can remove arc fault quickly to achieve the protection of LV/MV switchgear and bus.This thesis explains the causes of arc short-circuit fault in swichgear, impact and harm. We reserched on principle and implement technology of domestic and international existing bus protection solution, and compared advantages and disadvantages in protection principle, operation characteristics and installation situation. This thesis put forward the general scheme of arc protection system based on DSP, completed the hardware and software design of the system and carried on the preliminary engineering application.This arc protection system uses the principle of double criterion detecting both arc and overcurrent. Light is the most obvious and fastest-changing physical quantity of electric light, and it can be detected by arc sensor, ensuring rapid action. At the same time, in order to avoid tripping caused by external light interference, we use current detection part to check whether overcurrent to ensure reliability.This arc protection system consists of main control unit and expansion unit, and the main control unit can constitute minimum arc protection system for relatively simple applications. This thesis focuses on hardware design of main control unit and the main control unit uses combination of plug-in structure design, including power module, arc signal acquisition module, current signal acquisition module, CPU module, output control module, bus board and human-computer interaction module. Power module provides a stable12VDC to the main control unit. Arc signal acquisition module and current signal acquisition module are separately responsible for acquisiton, conversion and processing of arc light signal and AC current signal. CPU module is responsible for information collection, logic analysis, fault judgment and trip control of the entire system. Output control module is responsible for trip output control. Bus board conveys power supply for each board and is also responsible for data transmission of each plate and exchange of internal and external data. Human-computer interaction module is used for checking real-time operation by users and is easy for operation and management. About software design, this thesis mainly introduces flow chart of main program, initialization subprogram, signal processing subprogram and key processing subprogram.This thesis also introduces test, engineering application design and project installation of arc protection system, including installation diagram, basic requirements and methods as well as scene photographs. This thesis introduces the commissioning and operation in a coal mine in Zibo, Shandong. Through statistics records of field staff, there is no fault, refuse tripping or communication interruption. The operation practice shows that performance of arc protection system reached targeted goals and meet customers’ requirements.This arc protection system can clear fault fastly, and the duration of fault arc effectively shortens, which can make arc damage to electrical equipment greatly reduced and eliminate harm to human body as well. It can also prevent further expansion of fault, to avoid damage to the main transformer caused by long-time short-circuit current.