Abstract
Although the increase in frequency improves the transmission efficiency of high-frequency transformer, a higher probability of insulation failure is caused by high-frequency partial discharges. Through a high-frequency experimental platform, emission spectrum tests on two types of insulation faults were carried out under high-frequency square wave voltages. Subsequently, the influence of frequency and voltage amplitude on the light intensity and the number of photons of emission spectrum caused by air corona were studied. Finally, the variation of the spectrum of the partial discharge occurring at the interface of gas-solid insulation with frequency was analyzed. The results show that, the characteristic spectrum of air corona is composed of the near-ultraviolet spectrum, which is caused by the energy level transition of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> molecules, and the number of photons of air corona is positively correlated with voltage amplitude and frequency. Partial discharges at the gas-solid insulation interface have band spectrums in the visible light region and the near-infrared light region except for the near-ultraviolet spectrum due to the energy level transitions of outer layer electronics and the vibrations of C-H chemical bonds of PET molecules. This paper preliminarily verified the feasibility of applying the emission spectrum diagnostic method to two typical partial faults under high-frequency square wave voltages.
Highlights
The solid-state transformer (SST) has been widely used in smart grid and distributed energy systems for its lower volume and higher transmission efficiency
KV and frequency of 1~20 kHz, which is connected to the electrode through protective resistance; b) test chamber is used for performing Partial discharge (PD), and observation windows inlaid with optical glasses are opened on the outside of the chamber; c) electrical signal detection system composed of high voltage probe and oscilloscope, which is used for measuring high-frequency voltage; d) optical signal detection system composed of optical fiber probes and spectrum analyzer, which is used for detecting the wavelength and intensity of emission spectrum caused by PDs; e) Ocean View is selected as the spectral analysis software, which is used for statistics and analysis of the detected spectra
The characteristic spectrum of air corona is composed of the near-ultraviolet spectrum in the wavelength range of 315.64~405.12 nm, which is caused by the energy level transition of N2 molecules
Summary
The solid-state transformer (SST) has been widely used in smart grid and distributed energy systems for its lower volume and higher transmission efficiency. Some studies have indicated that the partial discharge properties including the number of discharges, discharge energy and phenomena under high frequency square wave voltages are different from those under the power frequency sinusoidal voltages [8]-[10]. Due to the partial discharge has the phenomenon of electromagnetic and acoustic wave, existing diagnostic methods for corona discharge under 50 Hz or 60 Hz mainly include the pulse current, radio frequency (RF), ultra-high frequency (UHF) and acoustic emission (AE) methods. The influence of frequency and voltage amplitude on the relative light intensity and the number of photons of emission spectrum caused by air corona were studied. The analysis of the spectral properties of PDs under high frequency voltage provides a theoretical reference for the proposal of online detection of partial discharge of HV-HF transformers
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