The Workers Frequency Very Slightly In The Grid Of Ultra-low Frequency Voltage Signal Detection Technology Research

Power System Stabilizer (PSS) Test is one of the conventional tests of Generator Excitation System. There is an indispensable equipment for Power System Stabilizer (PSS) Test, with the name of ultra-low frequency voltage detection instrument. This is a device which can take ultra-low frequency oscillation voltage signal with voltage of 10～100mV,frequency of 0～5Hz, from frequency grid with voltage of 100V, frequency of 50Hz.Because the domestic demand of this special equipment is limited and the kind of equipment needs for high technical, there are no specific domestic manufacturers make this product. About 10 years ago, When China began to carry out Power System Stabilizer Test for various large and medium sized power station generators, a relevant scientific research department of the Chinese Academy of Sciences developed an small amount of ultra-low frequency voltage detection instrument for its cooperation organizations. Soon because of other reasons, the department didn't make this product any more.At the same time, technology of ultra-low frequency voltage signal detection is kept strictly confidential. The project was commissioned by the Department of Yunnan Electric Power Test. We researched FLC-3 ultra-low frequency voltage detection instrument which had been urgently needed.On the case of no relevant paper and material can be referenced and provided, we identified a number of technical difficulties and resolved the issues with relevant testing methods of proof by the way of accessing relevant information. The most important innovations are that we proposed:first, With high-fidelity isolation transformer as the carrier, the signal input to the main system without distortion; second, three-phase rectifier circuit with the characterized of small filter constant and low-power can take out useful signal; Third, by the combination way of static cut and dynamic cut, not only the signal peak voltage drops to the scope that an ordinary low-power electronic component can withstand but also useful signal still be retained. Forth, the filtering part which as the main channel adopts voltage-controlled voltage source second-order low-pass filter circuit, which has the function of a cut-off point gain boost. fifth, by a comprehensive solution way with the characteristic of a adjustable gain amplifier as the final stage output, we solved the problem successfully that the signal with frequency less than 0.2Hz reduces too large through the prototype which made by the original scientific research department. Our products have passed field tests and applied in many PSS tests for power plants in Yunnan province rapidly, which proves our design achieves the desired results.This article reviews the development process of Power System Stabilizer (PSS). On the basis of this, it also discusses the theoretical basis related to the completion of the project, such as PSS-1A model,PSS-2A model,the theory of first-order and second-order low-pass filter circuits,the detection techniques of ultra-low-frequency and small-amplitude signal,the features of LM324 integrated operational amplifier circuit and so on. On the other side, Surrounded the implementation of the project, this article discusses the composition of the circuits theory, design and calculation way particularly about the whole system which include 7 cell circuits named isolation circuit, three-phase rectifier filter circuit, passive static cutting circuit, active dynamic cut circuit, second-order low-pass filter circuit, gain adjustment and output limiter circuits, power circuit. At last, this article shows the measured data, parts of the user documents such as debugging, troubleshooting methods etc.