Research On Leakage Current Detection Technology Based On Lock-in Amplification Principle

As power grid systems become more complex,ensuring that power systems can reliably provide power is a primary concern.In order to prevent large-scale power outage caused by insulator accidents,it is necessary to monitor the operation of insulators on the transmission line in real time,and the change of leakage current can clearly reflect the working condition,so it is important to measure the leakage current accurately.However,the conventional detection method cannot accurately measure the weak power frequency leakage current signal in a strong noise interference environment.Therefore,this paper introduces the weak signal detection technology,and designs a detection system based on the quadrature vector lock-in amplifier,which is used to measure the power frequency leakage current of the insulator of the transmission line.Firstly,the paper introduces the main working principle of the lock-in amplifier.The core of the detection system is the orthogonal vector structure lock-in amplifier based on the principle of cross-correlation.Simulink is used to build the structure model for simulation and verification.Then,each component of the quadrature lock-in amplifier detection system is designed in detail.It consists of a three-parts circuit signal channel module,which is a first stage differential amplifier circuit with low noise and strong anti-interference ability,a secondary amplifier circuit with improved amplification gain,and an automatic tracking band-pass filter with switched capacitor filter as the core.The reference channel module is composed of a square wave signal generating circuit that realizes square wave shaping and a quadrature signal generating circuit that takes phase-locked loop frequency multiplication technology as the core.The correlator module is composed of a phase sensitive detection circuit and a fourth-order low-pass filter,with the electronic switch type phase sensitive detection chip AD630 as the core.The system power supply module can provide a variety of levels.The data acquisition and processing module is composed of F28335 microprocessor module,AD7606 analog-to-digital conversion module,communication circuit and human-computer interaction circuit.Finally,the function of each module circuit is debugged,and the weak power frequency signals of different amplitude and signal-to-noise ratios are measured by using the designed detection system.The experimental results show that the system has good noise suppression capability,good linearity and high measurement sensitivity.