The Design Of Power Transformer’s Digital Protection Device

Power transformers play a key role in the process of power transmission, and are of one of the most important primary electric equipment. Its reliability will directly determine whether the power system works safety or not.So the design of the transformer protection is very important. The protection devices are often equipped with the main protection devices and the back-up ones to complete the protection of power transformers. There are two main types of transformer faults both in the internal and external. The main protection of the transformer is responsible for the internal faults and the back-up one is responsible for the external faults. When the main protection resist taking action,the backup protection will act. This paper mainly made in-depth research on the transmission protection. And after the study of its working principle, a new type of protection device has been designed.This paper have detailed discuss the principle of the main and back-up protection, including differential protection and differential quick break of main protection and over-current and overload of back-up protection device. The differential protection may cause fault action because of the inrush current. And this paper gives a detailed illustration about the reason of how the inrush current comes and the measures of how to avoid it. The transformer may cause unbalanced current in its normal operation, so this paper gives a detailed explain of the reason of the unbalanced current and inrush current and how to avoid them. The constant values of the device criterion come from the Fourier conversion therefore it has detailed interpretation of how to compute the value of fundamental wave, the second harmonic, the third harmonic and so on.This paper focuses on the design of hardware and software system of protection device, and fully considers anti-interference measures. The hardware system uses the plug-in structure which is widely used. The modules are both independent of each other and also work as a team to protect the transformer realizing all the functions including the network communication. The hardware structure is based on the high-performance CPU TMS320F2811 of TI corporation, completing all the functions including data acquisition, logic input and output, HMI, network communication of the microcomputer protection. The exploit of software system is conducted in the CCS software environment. By combining the main program and interrupt program, greatly improve the working efficiency and reduce the power consumption using the powerful data processing and control ability. DSP takes full advantage of abundant peripheral resources on-chip to complete the functions like A/D conversion and serial communication. This article made a detailed introduction of its software process.The speed and precision of the protection device satisfy the requirements of the microcomputer protection. To confirm for it, do the commissioning to proof the main functions, including network communication experiment.