Comparison of PD and Breakdown Characteristics Induced by Metal Particles and Bubbles in Flowing Transformer Oil

Abstract

Metal particles and bubbles are two typical impurities in transformer oil that can cause partial discharge (PD) and even electric breakdown. The PD characteristics are closely related to the motions of these impurities in flowing transformer oil. In this paper, the motions of impurities were obtained by a camera and a simulation model at first. Then, we employed three methods, namely, antennas, a non-inductive resistor, and the method recommended by IEC 60270, to measure the PD signals simultaneously. The breakdown experiments of transformer oil containing the metal particles and bubbles were also performed. In terms of these, single PD waveforms, statistical characteristics, and breakdown voltage were obtained. The results showed that the metal particles could excite ultrahigh frequency (300 MHz-3 GHz) PD signals, whereas bubbles only excited signals in the very high-frequency band (30-300 MHz). Moreover, the PDs induced by the metal particles had a higher repetition rate and a smaller amplitude than the PDs induced by bubbles. In addition, the metal particles easily caused PD, whereas bubbles easily led to the breakdown. Possible reasons for different discharge characteristics between the two impurities were discussed on the basis of the motions of impurities and the distortions of electric field.INDEX TERMS Metal particle, bubble, partial discharge, breakdown, flowing transformer oil.

Effect of Floating Metallic Particles in Pre-Breakdown and Breakdown Characteristics of Oil Transformer under DC Voltage

“…The experi-ment setup was depicted in Figure 1, while its realization at the laboratory was shown in Figure 2. The test circuit consisted of a high voltage transformer (1), a diode (2), a smoothing capacitor (3), two measuring resistors (4), a damping resistor (5), a grounding switch (6), a set of the test object (7), an arrester tube (8), a resistor 56 Ω (9), an oscilloscope (10), a digital measuring instrument (11), and a camera (12). The specification for each component of the high voltage generator can be seen in Table 1.…”

“…In addition to the applied voltage type (DC, AC, or composite), liquid viscosity, and parameters related to the particles themselves, the liquid motion may affect the particle trajectories whereby the PD characteristics may be exaggerated. Recently, a research group actively investigated partial discharge activity on flowing trans-former oil contaminated by metallic particles under different operating temperatures, velocity, applied voltage, and particle concentration [11][12][13][14]. They found that the metallic particles increased partial discharge activity and lower breakdown voltage, but moving oil helped reduce partial discharge activity.…”

The Generation and Migration of Bubbles in Oil-Pressboard Insulation Needle-Plate System

“…Photographing the bubble positions over time in a horizontal oil pipeline allows one to analyze how temperature and applied voltage affect the trajectory of bubbles in horizontal oil pipelines. The results show that the movement of bubbles is divided into two phases: a rising phase and a horizontal phase [17,18]. However, these studies assume a uniform electric field when discussing bubble migration.…”

Extraction of Partial Discharge Signal in Predominantly VHF Frequency Range in the Presence of Strong Noise in Power Transformer

“…c) Free (metal, cellulose) particles in transformer oil [10,11]. d) Gas bubbles in transformer oil [12][13][14][15][16]. e) Surface tracking on an oil-impregnated pressboard [17][18][19].…”