A novel cloud model for risk analysis of water inrush in karst tunnels
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Inrush current
The purpose of the paper is to realize the dynamic modification and management of the full course of the assessment on the karst water inrush risks. In the paper,first,the distance between the karst caves and the tunnel in the profile map is estimated by means of semi-quantative analysis method on basis of the development and distribution rules of the karst; secondly,the prediction of the safe thickness of the karst water inrush resisting rock strata is divided into three stages,i. e.,the preliminary estimation stage,the secondary estimation stage and the dynamic calculation stage,for which effective modification methods are adopted so as to obtain more accurate and more appropriate prediction values for the safe thickness of the karst water inrush resisting rock strata; thirdly,the evaluation standard for the probability level of the karst water inrush risks is proposed on basis of the safe thickness of the water inrush resisting rock strata and the disturbance depth of the excavation blasting,the evaluation standard for the consequence level of the karst water inrush risks is proposed by means of classifying the water inrush volumes and the water pressures in the karst chamber,and the assessment matrix for the grades of the karst water inrush risks is established; Finally,the assessment model for the karst water inrush risks based on the karst distribution pattern and the karst water inrush resisting rock strata is established. The comparison and contrast between the theoretical result and the actual conditions in the engineering cases verifies the rationality and feasibility of the karst water inrush risk assessment model.
Inrush current
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Abstract Transformers in power system usually take current differential protection as the main protection, but the protection is easy to be affected by inrush currents and then maloperates. Sympathetic inrush is one kind of inrush currents, which is caused by energization of an adjacent transformer. There were many transformer differential protection maloperation cases caused by sympathetic inrush in the field, while the conventional second harmonic restraint method did not work effectively. In this paper, a method based on substation-area currents and curve fitting is proposed to identify sympathetic inrush. The method is presented using the characteristic that sympathetic inrush and initial inrush alternatively appear in reverse polarities. The characteristic exists continuously during sympathetic inrush. In order to verify effectiveness of the proposed method, PSCAD/EMTDC software is used in this paper to build sympathetic inrush model and obtain simulation data. Simulation results prove that the proposed method can effectively identify sympathetic inrush.
Inrush current
Differential protection
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Abstract In order to effectively evaluate the facilities in each airport airfield, this paper proposes four methods: analytic hierarchy process (AHP), subjective weighting method based on Improved Analytic Hierarchy Process (AHP), objective weighting method based on entropy weight method and combination weighting method based on game theory. Combined with the actual situation of the airport, the corresponding calculation method is adopted to introduce the mathematical model into the construction of the airport. After verification, the proposed method can be applied to 90% of airports, and the applicability of the index is improved by 50%. The weight of obstacle capability evaluation index provides an important basis.
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Landform
Sinkhole
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Transformers is one of the most critical equipments for electrical energy transfers in a power system. In several cases, magnetizing inrush phenomenon can lead to mal-operation of differential & REF protection. The phenomenon of magnetizing inrush is a transient condition that occurs when any abrupt changes of the magnetizing voltage. It is not fault condition, and therefore transformer protection must remain stable during the transient condition.This paper describes and analyzes a case studies where protective relay with magnetizing inrush restraint still send tripping signal when the magnetizing inrush happen. This paper uses fault wave recording to discuss the operation behavior and reasons of corresponding protection relay. The results of the studies confirm that the magnetizing inrush current event affects not only differential protection but also REF protection.
Inrush current
Differential protection
Tripping
Transient (computer programming)
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This paper presents a new approach to developing techniques for the inrush restraint based on wavelet for transformer differential relays. When a power transformer is energized, the resulting inrush current can cause a differential relay to issue a false trip signal. The establishment of inrush in power transformer is becoming unreliable in existing numerical protection. The presented technique is based on the detection of inrush generated transient signals using wavelet analysis. The results of simulation indicate that the proposed method is very effective in detecting inrush with a high accuracy and reliability.
Inrush current
Differential protection
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A transformer model was built using PSCAD. The generation mechanism, waveform characteristics and influence factors of inrush current were simulated and analyzed. Combined with transformer differential protection, this paper discussed the conventional methods to identify inrush current and the operation logic to prevent mal-operation caused by inrush current. The typical transformer differential protection operating criteria were also simulated under different fault conditions. The results show that digital simulation can properly present inrush current waveform characteristics, different kinds of transformer fault status and inrush current influence on differential protection.
Inrush current
Differential protection
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Power transformer inrush current discrimination has always been the main task of transformer current differential protection. The power transformer will generate two kinds of inrush currents, namely, the sympathetic inrush current and the magnetizing inrush current. It is still a difficult problem to distinguish the two inrush currents of the power transformer. In this thesis, MATLAB is used to simulate and analyze the sympathetic inrush current and the magnetizing inrush current of three-phase transformers. The characteristics of the two waveforms are simulated. The simulation analysis of the sympathetic inrush current and magnetizing inrush current will help the inrush current of the transformer. methodological study.
Inrush current
Differential protection
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Power transformer is one of the most important equipment of power system, but the inrush current in transformer easily leads to malfunction of differential protection, which results in an impact on the normal operation of the power grid. This paper conducted a theoretical study on the forming mechanism of inrush current and carried out simulation analysis using MATLAB software. The paper analyzed the characteristics and hazards of inrush current, also it summed up the methods to deal with inrush current of transformer. In the end, the paper conducted a research on a project which has malfunction caused by the inrush current and then it proposed the reasonable solutions.
Inrush current
Differential protection
Power grid
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Albania is one of the most karst-developed countries in Europe. Karst phenomena are related to soluted carbonate formations which cover of about 7300 km2 of Albanian territory and with sulfate evaporates rocks, which outcrop of about 500 km2. Typically alpine relief of average altitude 708 m above the sea level and high horizontal splitting are favorable for karst development. Karst and geological sites of karst origin are widespread mainly in Albanian Alps and in Ionian zone. In Albanides there are determined surfaces and underground karst forms which belong to the Neo-Pliocene-Quaternary age and deep karst forms belonging to the paleokarst in old formations. The most widespread karst forms in carbonate rocks there are valleys, caves, cones etc., while into salt rocks there are formed many karstic lakes and depressions. Up to now there are determined about 80 karstic caves, nice karst fields, valleys, plains, which represent geological sites of karst origin.
Outcrop
Sinkhole
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