Abstract
Partial discharge (PD) measurement and its pattern recognition are vital to fault diagnosis of transformers, especially to those traction substation transformers undergoing repetitive traction load shocks. This paper presents the primary factors induced by traction load shocks including high total harmonics distortion (THD), transient voltage impulse and high-temperature rise, and their effects on the feature parameters of PD. Experimental tests are conducted on six artificial PD models with these factors introduced one by one. Results reveal that the maximum PD quantity and the PD repetitive rate are favorable to be enlarged when the oil temperature exceeds 80 °C or the THD is higher than 16% with certain orders of harmonic. The decline in PD inception voltage can mainly be attributed to the transient voltage impulse. The variation in central frequency of the fast Fourier transformation (FFT) spectra transformed from ultra-high frequency signals can mainly be attributed to high THD, especially when it exceeds 20%. The temperature rise has no significant influence on the FFT spectra; the transient voltage impulse, however, can result in a central frequency shift of the floating particle discharge. With the rapid development of high-speed railways, the study presented in this paper will be helpful for field PD detection and recognition of traction substation transformers in the future.
Highlights
Traction substation transformers are one of the key components of the traction power supply and distribution system of a high-speed railway
Compared with the Fourier transformation (FFT) spectrum derived under variable total harmonics distortion in Section 3.1, the temperature has no significant impact on the central frequency except for some small pseudodominant frequency intervals and a slight increase in the accumulated amplitude of the FFT spectrum
The total harmonics distortions, the temperature rise, and the transient voltage impulse induced by traction load shocks were considered as three principal factors that influence the partial discharge (PD) characteristics of traction substation transformers
Summary
Traction substation transformers are one of the key components of the traction power supply and distribution system of a high-speed railway. The oil/paper insulation of traction substation transformers, compared with general power transformers, must withstand stresses caused by non-periodic and short-time load shocks, high-temperature rises, and transient overvoltages, etc. This will lead to a resonant overvoltage in the traction power supply and distribution system [6] Under such operation conditions, the technical requirements for traction substation transformers (i.e., limitation of temperature rise, load curves, shortcircuit times, etc.) are much higher compared with those of regular power transformers [7,8,9].
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