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A novel multi-function saturated-core fault current limiter (MFCL) with two operating modes is proposed in this paper. MFCL can achieve fault current limitation and power flow management by switching operating mode: current-limiting mode and power-flow-controlling mode, which realizes technology convergence. The MFCL consists of an iron core with rotatable magnetic valve, ac coils, dc coils, and a fault-limiting reactor. The operating principle of the MFCL and the design of the rotatable magnetic valve are analyzed in this paper. The finite-element analysis (FEA) model based on Maxwell is used to analyze the MFCL. Simulation results depict that the MFCL can limit fault current effectively and provide variable impedance for power flow controlling.

Dissolved gas analysis (DGA) has an essential role to transformer status. A gas sensor is fabricated for DGA by using the developed one-dimensional polycrystalline SnO2 fiber material. On basis of this, a portable gas chromatographic device (PGCD) is developed for DGA. A wavelet-genetic algorithm (GA) threshold denoising method is proposed for noise reduction and applied to chromatogram to detect the weak peaks of the PGCD for latent transformer faults. Then, an improved filter matching method based on gray incidence degrees for peaks detection is presented to overcome the limitations of the derivative method. Results indicate that the proposed signal processing method demonstrates competitive performance, thereby providing a favorable foundation for quantitative analysis. Tests were conducted to measure the repeatability and accuracy of the developed polycrystalline SnO2 sensor and PGCD. Comparison with the commonly used flame ionization detector is performed, and the effectiveness of the developed sensor and the corresponding PGCD are verified.

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.

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.

The fluctuation of electrical power load is affected by numerous external factors, such as climate change, economic development, social form and special events etc. The optimal feature subset selection is the key to improving the accuracy of short-term power load forecasting. The traditional feature selection methods have encountered difficulties in balancing performance and computational consumption. The development of ensemble feature selection methods is a feasible way to solve this dilemma. In this paper, an embedded ensemble feature selection method is established and investigated on a short-term electrical load forecasting task. A new weighting approach is proposed to combine the result of individual embedded feature selection methods. The results of the embedded ensemble feature selection method show a significant increase in accuracy compared to the individual feature selection methods.

In this paper, transformer DC magnetic bias caused by rail transit stray current is researched. The logic relation and core elements of stray current and DC magnetic bias are analyzed. The mathematics model is instituted through the data from subway operation and power grid monitoring. This model can not only be used for the assessment and treatment of transformer DC magnetic bias, but also can be used to locate the weak points of train track insulation. At the same time, this paper provides a combined stray current control scheme for two different systems of power grid and urban rail transit, which have been achieved remarkable results in Changsha area.

This paper starts from the regular phenomenon of transformer DC magnetic bias caused by ground - into stray DC. The distribution mechanism of stray current in the soil is analyzed and the multi-system coupling mathematical model for corrosion evaluation and seismic source prediction is constructed. Then, the data of power grid, oil pipeline and geomagnetic intensity in Hunan Province are input into the model for simulation. Effective prevention and prediction programs are obtained. Moreover, this paper provides reference for the application of the calculation and analysis of ground-into stray DC to other industries besides power system.

Wild fire is one of the most serious natural disasters threatening the electric grid. This article analyzes the risk of wild fire on electric grid transmission lines considering cascading failure. In order to meet the timeliness requirement of on-line analysis of power grid under wild fire disaster, an improved sampling method considering the sequence of fire tripping is proposed. Thus, the risk ranking of transmission lines considering cascading failures of wild fire can be obtained, according to that, the optimal emergency strategy can be formulated for the electric grid. The effectiveness and validity of the proposed framework and method are demonstrated by application examples.

It is of great significance to develop functional coatings for uhv transmission lines which according to the working conditions and service environment to improve the safety, stability and economy of uhv transmission lines. This paper focuses on the latest research progress of uhv insulator functional coatings in recent years, including anti-fouling flashover coatings and anti-icing coatings. The preparation methods, main performance parameters, application conditions and existing problems of the two coatings were throughly discussed and the future development and research direction were also pointed out.

DC magnetic bias refers to a series of complicated electrical, magnetic, force, sound, heat and other abnormal phenomena caused by DC current intrusion into the transformer winding, which causes half-cycle saturation of core flux, which will seriously endanger the safe and stable operation of the transformer. Since the 1000kV UHV substation is very important in the power system, and the UHV transformer has lower DC current tolerance than the general transformer, it is necessary to accurately evaluate the DC bias risk of the UHV transformer during the design phase. This paper provides a reference for the DC bias magnetization prevention and control of UHV transformers by modelling and analysing the DC bias magnetization of 1000 kV UHV substation in Changsha. .

In this paper, the big data analysis method is applied to the analysis of the factors affecting the DC magnetic bias of the transformer. The improved k-means clustering algorithm is used to identify the different magnetic reasons. The weighted relevance analysis is used to evaluate the influence of different factors on the magnetic current. Finally, the correctness of the method is verified by an example analysis, thus providing an effective basis for “one-button sequence control” DC magnetic bias treatment.

Transformer DC magnetic bias is difficult to accurately analyze and predict because it is caused by complex factors and has a wide influence. This paper combines big data with DC bias magnetic analysis method, making a breakthrough in the DC bias prediction model that only considers a single factor. From the perspective of multi-system coupling, this paper analyzes the modeling of DC magnetic bias based on multi-dimensional big data, and extracts the key influencing factors of transformer DC bias through multi-system big data cleaning and dimensionality reduction technology, thus providing an effective basis for "one-button sequence control" bias magnetic treatment.

The quantitative analysis methods of the total corrosive sulfur (TCS) in transformer oils were realized using copper powder corroding technique. In this technique, excess copper powder reacted with insulating oils at 150°C for 12 hours to form corrosion product (CU2S). Then, Cu2S was oxidized to CuSO4 2−, and finally dissolved to sulfate solution. There are three methods to test the amount of TCS. SO4 2− solution tested by ion chromatography (IC) or Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). Moreover, adopted ICP to test total sulfur (TS) in oils before and after corrosion reaction, and the difference value is the content of TCS. Comparing with these methods, it was found that ICP detection of total sulfur (TS) in oils could achieve excellent linearity. The correlation coefficients is R2≥0.999, and the recovery rate is 98.4%∼103.4%.

12kV vacuum circuit breaker(VCB) is widely used in distribution system. It is important to research its state and analyze its performance changes. In this paper, several 12kV VCBs which had been in service for several years were investigated. Mechanical operate experiment was carried out on them, mechanical parameters were recorded. It was found that 7.7 percent of VCBs' closing speed was higher than upper limit, while 23 percent of VCBs' opening speed exceeded upper limit. The longer the VCB was used, the bigger the dispersion of opening or closing speed was. The experiment results showed that primary loop component faults of VCB were related to the change of mechanical parameters. Meanwhile, a model of operating mechanism in ADAMS software was built, and the opening process under normal and fault circumstance were simulated. This mode analyzed the influence of circuit components fault on separate operation. Good coincidence was achieved with experimental data.

This paper presents a method to detect receptive capacity of external ultra-high frequency (UHF) senor for gas insulated switchgear (GIS) partial discharge (PD) testing using time-frequency reference method. It is always crucial to detect PD using UHF inspection device for live GIS, while the affection of senor performance on PD detecting accuracy is very important. So this paper, analyzing the disadvantages of existing inspection method for UHF capacity, makes use of time-frequency reference method to represent the receptive capacity for UHF senor. The standard unipolar probe antenna and pulse signal source are employed to inject signal and build electromagnetic field in GTEM cell. The receptive capacity for UHF senor is computed by combining spectra curve of unipolar probe antenna with the time-domain signals, which is tested by standard unipolar probe antenna and UHF senor. This paper achieves the objective of detecting receptive capacity for three UHF sensors by building up a detecting system, and detection results indicate that the method in this paper is effective to detecting receptive capacity for UHF senor.

Discontinuous leader development is the most important discharge process under the application of the switching impulse voltage with the low rate of voltage rising, which is of great significance to study the external insulation characteristics of ultra-high voltage (UHV) large scale air gap. Based on the CMOS high-speed camera, a discharge test with different operating impulse voltage is carried out by constructing a comprehensive observation platform of rod-plate air gap discharge, and a clear discontinuous leader development process picture is captured. Moreover, the leader current, injection charge and leader channel unit length charge, and their characteristics of the change trend are also obtained. Further analysis based on the experimental results shows that the discontinuous leader development under the action of the impulse voltage with low rate of voltage rising has two different laws. Finally, this paper uses the thermodynamic equation, combined with the test results, the channel temperature changes in the discontinuous leader development stagnation stage were calculated. The results show that the leader channel temperature is still greater than 1500 K in the hundreds of microsecond time scales in the leader stagnation stage, and the subsequent leader can continue to develop on the original leader channel.

(3-7) . The credibility of the lightning simulation experiment depends on how exactly it reconstructs the actual lightning attachment process. Over the past three decades, many experiments have been carried out in high-voltage laboratories to develop a more valid way to simulate the lightning attachment process by using long sparkle discharge. Most of these experiments were carried out by using two typical configurations. One is a rod-plane gap that the rod electrode is energized with positive impulse voltage and the plane is grounded potential (8) . It results in a positive leader incepting from the rod. Another typical configuration is an inverted rod-plane gap (5) . In this configuration, the overhead plane electrode is energized with negative impulse voltage and the rod is located on the ground at zero potential. It results a positive upward leader inception from the rod. In this paper, a traditional rod-plane gap is adopted. The rod electrode is energized with negative impulse voltage. The test object is replaced by a scaled model. Therefore, the encounter process of the downward leader and upward leader can be simulated by the negative streamer inception from the rod electrode and the upward streamer inception from the scaled model, respectively. The purpose of this paper is to investigate the lightning shielding performance of the HVDC transmission line concerning the effectiveness of dc operation voltage by employing a simulation experiment approach. Firstly, the equivalency of the scaled experiment is discussed from the following aspects: (a) the determination of test scale factor; (b) the electric field simulation of downward leader; (c) nominal field simulation of the HVDC transmission line. Secondly, a test circuit is established concerning the isolation of the dc charge circuit and surge generator. The exposure space distribution of the HVDC transmission line obtained from a large amount discharge experiments and the typical discharge phenomenon are described in section 3. Finally, the effect mechanism of the dc voltage on the lightning shielding performance of HVDC transmission line is preliminary analyzed according to the recorded phenomenon.

The paper analyses the monopolar grounding fault in bipolar HVDC system with phase-modal transformation method. Initial jumping voltage and maximum voltage on health pole with different kinds of termination are deduced by establishing the modal circuit under the fault. Simulation results show a grounding fault in the middle of the line exhibiting maximum voltage with value of 1.54 p.u, which agrees well with the theoretical value. And the maximum voltage decreases with the increasing grounding resistance. The inductance of the reactor influences the maximum voltage on health line a little.