Qiuqin Sun

An Online Monitoring System for Oil Immersed Power Transformer Based on SnO 2 GC Detector With a New Quantification Approach

In this paper, an online monitoring system based on a SnO2 gas chromatographic detector for power transformer condition assessment is developed. For a quantitative analysis of feature gases dissolved in transformer oil, a mathematical model derived from the chemistry and semiconductor theory is proposed. On the basis of this, gas chromatography measurement module along with electronic controlling and data sampling system is designed and integrated. A series of repeatability test and quantitative analysis has been performed; the repeatability performance is excellent for given concentrations; the measurement accuracy based on the proposed mathematical model for the feature gases shows good suitability. Furthermore, the transformer diagnosis is performed for identifying fault types. The experimental and practical application results demonstrate the effectiveness of this system.

Adsorption Mechanism of Cu-Doped SnO2 110 Surface toward H2 Dissolved in Power Transformer

The content of hydrogen is a key quantity in condition assessment and fault diagnosis of power transformer. Based on the density functional theory DFT, the adsorption mechanism of Cu-doped SnO2 surface toward H2 has been systematically studied in this work. Firstly, the relaxation, the bond length, and overlap population of both the pure and Cu-doped SnO2 are computed. To determine the optimal doping position, the formation energies of four potential sites i.e., Sn5c, Sn6c, Sn5c-s, and Sn6c-s are then compared with each other. The adsorption energy and the electronic structure of SnO2 surface are analysed and discussed in detail. Furthermore, to estimate the partial atomic charges and the electrical conductance, the Mulliken population analysis is also performed. It has been found that the bridge oxygen is the most favourable position. The partial density of states of H2 after adsorption is broadened and shifted close to the Fermi level. A large amount of charges would be transferred and then released back into its conduction band, leading to the reduction of resistance and the enhancement of sensitivity toward H2. The results of this work provide references for SnO2-based sensor design.

A Compact UHF Antenna Based on Complementary Fractal Technique

A compact and wideband ultra-high-frequency antenna is developed in this paper. By applying the Minkowski fractal geometry into both the lateral boundaries of monopole and the upper boundary of ground plane and loading the asymmetric strips at the top of monopole simultaneously, the miniaturization is realized; by means of adjusting the fractal direction to produce a complementary structure and cutting the triangular notch on the ground plane, the impedance bandwidth is enhanced. The influences of critical parameters on the impedance bandwidth are determined through the sensitivity analysis. Furthermore, to validate the performance of the proposed antenna, the return loss, radiation patterns, transfer function, and fidelity factors are measured; the electrical dimension and ratio bandwidth are compared with those of the existing antennas. It shows that the antenna with size of

Investigation on volt-ampere characteristic of secondary arc burning in atmospheric air

0.28\lambda _{L} \times 0.28\lambda _{L}

Parameter estimation of extended free-burning electric arc within 1 kA

can cover the frequency ranging from 700 MHz to 4.71 GHz and has an average gain of 3.93 dBi along with strong pulse handling capability. The results demonstrate the superiority of the complementary fractal technique.

SOFC detector for portable gas chromatography: High-sensitivity detection of dissolved gases in transformer oil

The secondary arc, as a common phenomenon in a high voltage power transmission system, is an essence of an electric arc. It not only damages the electrical power equipment but also threatens the safety of the power system. A series of experiments on the secondary arc have been conducted in this work. The volt-ampere curves are measured, the motion trajectories are captured, and the centroid of the secondary arc body is calculated by means of image processing. The experimental results indicate that the secondary arc length can reach several meters, and its volt-ampere curve is completely different from that of short-gap arcs and others operated in some special dielectrics such as vacuum. The evolution of the secondary arc can be generally divided into two stages. In the early stage, the arc column performs a vertical motion and has an upward trend due to thermal buoyancy. Basically, the volt-ampere curve has a shape of a regular hysteresis loop. The impacts of the frequent short-circuit behavior of the arc column on the volt-ampere curve and arcing time are investigated. At the later stage, the secondary arc temperature drops and the zero-off behavior becomes obvious. The volt-ampere curve is inevitably affected. The zero-off duration is obtained, and the key factors are discussed. The dynamics of charged particles in the zero-off interval are analyzed. Furthermore, under the effect of strong wind, it has been found that the secondary arc current is occasionally forced to zero and preceded by the voltage. The mechanism for such a phenomenon is first elucidated from the perspective of energy balance. The results lay a theoretical basis for secondary arc physics.The secondary arc, as a common phenomenon in a high voltage power transmission system, is an essence of an electric arc. It not only damages the electrical power equipment but also threatens the safety of the power system. A series of experiments on the secondary arc have been conducted in this work. The volt-ampere curves are measured, the motion trajectories are captured, and the centroid of the secondary arc body is calculated by means of image processing. The experimental results indicate that the secondary arc length can reach several meters, and its volt-ampere curve is completely different from that of short-gap arcs and others operated in some special dielectrics such as vacuum. The evolution of the secondary arc can be generally divided into two stages. In the early stage, the arc column performs a vertical motion and has an upward trend due to thermal buoyancy. Basically, the volt-ampere curve has a shape of a regular hysteresis loop. The impacts of the frequent short-circuit behavior of the arc...

Hybrid RVM–ANFIS algorithm for transformer fault diagnosis

A long electric arc, as a common phenomenon in the power system, not only damages the electrical equipment but also threatens the safety of the system. In this work, a series of tests on a long electric arc in free air have been conducted. The arc voltage and current data were obtained, and the arc trajectories were captured using a high speed camera. The arc images were digitally processed by means of edge detection, and the length is formulated and achieved. Based on the experimental data, the characteristics of the long arc are discussed. It shows that the arc voltage waveform is close to the square wave with high-frequency components, whereas the current is almost sinusoidal. As the arc length elongates, the arc voltage and the resistance increase sharply. The arc takes a spiral shape with the effect of magnetic forces. The arc length will shorten briefly with the occurrence of the short-circuit phenomenon. Based on the classical Mayr model, the parameters of the long electric arc, including voltage gradient and time constant, with different lengths and current amplitudes are estimated using the linear least-square method. To reduce the computational error, segmentation interpolation is also employed. The results show that the voltage gradient of the long arc is mainly determined by the current amplitude but almost independent of the arc length. However, the time constant is jointly governed by these two variables. The voltage gradient of the arc with the current amplitude at 200–800 A is in the range of 3.9 V/cm–20 V/cm, and the voltage gradient decreases with the increase in current.A long electric arc, as a common phenomenon in the power system, not only damages the electrical equipment but also threatens the safety of the system. In this work, a series of tests on a long electric arc in free air have been conducted. The arc voltage and current data were obtained, and the arc trajectories were captured using a high speed camera. The arc images were digitally processed by means of edge detection, and the length is formulated and achieved. Based on the experimental data, the characteristics of the long arc are discussed. It shows that the arc voltage waveform is close to the square wave with high-frequency components, whereas the current is almost sinusoidal. As the arc length elongates, the arc voltage and the resistance increase sharply. The arc takes a spiral shape with the effect of magnetic forces. The arc length will shorten briefly with the occurrence of the short-circuit phenomenon. Based on the classical Mayr model, the parameters of the long electric arc, including voltage g...

A novel UHF Minkowski fractal antenna for partial discharge detection

Dissolved gas analysis (DGA) is widely used in diagnosing the incipient faults of power transformer. The detector is the key component for this method. Despite various sensors for DGA application, many of them suffer from poor stability and low sensitivity. A solid oxide fuel cell (SOFC) detector is designed in this paper to address these problems. The mechanism of the detector is briefly introduced, and it is fabricated in a mold. The test process is elucidated. For calibration purpose, two mathematical models of the detector, i.e., double-logarithmic model (DLM) and linearity model (LM), are compared with each other. Experimental results demonstrate that the SOFC detector exhibits good repeatability at given concentrations and excellent linearity with DLM. The results indicate that accurate and high-precision measurement of H2, CH4, CO, C2H4, C2H6, and C2H2 can be achieved using the SOFC detector and the proposed DLM.