Design of self-powered digital over-current protector

All along, most of the relay protection device´s own power supply of work and operation circuits requires substation or distribution room to provide AC or DC power supply. This paper introduces hardware and software design of self-powered microcomputer relay protection device. The energy is obtained directly from the power line by some tailor-made iron core current transformer (CT). The signal, output of the rectifier circuit, is the input signal of sampling circuit and can also charge energy storage capacitor at the same time. An integrated switching regulator changes voltage signal, terminal of the energy storage capacitor, into stable DC voltage signal, as the DC regulated power supply of digital relay. Real-time control and multi-tasks scheduling method is used in software design, which can realize the function of sampling, AD conversion, display, protection etc. In the SCM system, the introduction of multi-task system can improve the program structure to meet the requirements of complex system, and makes program debugging and maintenance easier.