Research And Design Of The Main Transformer Protection Equipment Based On Embedded Technology

The power industry is a pillar industry of the national economy. With the development of national economy, demand for electricity and power distribution reliability becomes higher. In modern power system, power grid may interrupt due to the disturbance, while relay protection can promptly provide some correct electrical equipments to respond the disturbance. Power transformer is important, thus indispensable to power grid. Whether transformer relay protection can make accurate and reliable action is important to the power grid. This paper focuses on the power transformer, making study on its main protection equipment.Firstly, the current status of transformer protection home and abroad is analyzed in this paper. Using MATLAB to simulate the excitation inrush currents and a variety of ground fault currents and then applying FFT analysis and wavelet analysis on fault waveforms and excitation inrush current waveforms based on study the principle of transformer protection and the characteristics of Ratio braking. Comparing the wavelet analysis with FFT analysis to propose excitation inrush current identification method based on wavelet transform.Secondly, introduce the hardware system design of transformer protection device. Hardware system comprised by DSP+ARM is designed in this paper. Protection board takes DSP chip-TMS320F2812 as the core; it is mainly used for collecting voltage and current, then calculating the differential current-lop, braking current Ir and second harmonic RMS. At the same time, perform the corresponding protection program according to the preset transformer protection setting values. When the differential protection judgment meets the trip conditions, control output of switch to remove the point of failure. Then, the fault information displays on the management board through SPI communication. Management board uses ARM chip-LM3S6965 as the main controller; the management board makes date communication with upper computer through Ethernet communication interface.In addition, introduce software program for each function module of the transformer protection, including A/D sampling program, frequency capture program, FFT program, exception handles and Ethernet communication program. Through combination of both hardware and software, this paper completes the test of each function module, and obtains relatively ideal results.Experimental results show that the design of the main transformer protection reaches the expected goal of design. It can achieve the desired differential protection, zero sequence over current protection of typical fault.