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In order to deal with harmonics of converter transformers in UHVDC transmission systems, the first task is to accurately detect the harmonic components. This study constructed a detection system for measuring and analyzing AC side harmonics of converter transformers. This detection system combines the following functions: extraction of AC current signals, conversion from analog signal to digital signal, data transmission via optical fiber, and conversion from time domain to frequency domain based on Fourier transform theory. The detection system is composed of hardware and software, including flexible CT, remote signal high-speed acquisition module, local signal conversion module and data analysis module developed using LabVIEW and MATLAB. The winding current can be precisely collected at the grid side bushing of the converter transformer. The optical fiber connection between the remote signal acquisition and local signal conversion module can effectively prevent electromagnetic interference. This detection system can collect the current signal in real time, and perform the harmonic analysis in time and frequency domain. This paper presented details of the detection system and the harmonic characteristics of the converter transformer at grid side under different operating conditions.
Inspec keywords: virtual instrumentation; harmonic analysis; signal detection; data analysis; power system harmonics; Fourier transforms; electromagnetic interference; data acquisition; signal processing; frequency-domain analysis; power system measurement; HVDC power transmission
Subjects: Power system measurement and metering; d.c. transmission; Electromagnetic compatibility and interference; Computerised instrumentation; Control of electric power systems; Signal detection; Power supply quality and harmonics