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The dissolved gas in transformer oil, which could represents the transformer faults, can be analyzed by spectroscopy. Since the BP neural network method involves a large amount of data matrices operation which leads to much computation and that single computer can not meet the requirements of real-time analysis. In order to improve the situation, this paper proposes a quantitative spectral analysis...
To reduce the negative effects caused by electric vehicles (EVs), this paper proposes a coordinated charging strategy for batteries in EV charging station. According to the charging characteristics of EV batteries, the strategy is established to minimize the sum of squares of the substation, which could consider the number of battery chargers, EVs' needs for batteries, power limit of EV charging and...
Based on the phase transform technique, the phase transformation matrix is established according to the phase shift relations of three-sequence state variables between two sides of transformer. A novel processing method of transformer branches is proposed, which can be efficiently introduced into a decoupled three-phase power flow algorithm for distribution networks containing multi-transformer-branches...
Dynamic performance of grid connected doubly-fed induction generator (DFIG) in electromagnetic timescale is not merely determined by the operating point, but also largely dependent on its converter control. DFIG may suffer stability issues when integrated into a weak AC grid, in which converter control loops are coupled, and resulted impact for system stability is obscure. This paper proposed a simplified...
As the electric vehicle(EV)charging is playing an important role in distribution network, it has attracted more and more attention. In order to clarify the relationship between the operation mode of EVs, peak charging load and peak power load of grid, this paper defines two key parameters: coincidence factor and mutual coincidence factor. The variation tendencies of these two parameters under different...
The islanding problem in grid-connected photoltaics system and traditional islanding detecting methods are studied. A new method using the voltage harmonic is proposed in this paper. The method has high response speed and no influence on the power quality of the system. The simulation model is built by PSCAD/EMTDC, and MATLAB is used to implement the algorithm. The simulation results showed that the...
A novel three-phase series-connected modular multilevel converter in T configuration (TSC-MMC) for high voltage direct current transmission system is presented. The paper studies the dynamic mathematical model and the control scheme based on the proposed topology. Compared to conventional MMC, the number of IGBTs in TSC-MMC is reduced when withstanding the same dc voltage, which effectively decreases...
The reasonable transmission efficiency of power grid was analyzed considering to N−1 and power outrage risk constraint respectively in this paper. The representative index of security and efficiency had been selected to reflect the condition of power grid. In the aspect of security, the N−1 Pass ratio represented the determinacy index and the power outage risks represented a non-determinacy index...
With the development of the economy, gas-insulated metal-enclosure switchgear (GIS) is widely used for its good economic benefits and other advantages. At the same time faults of GIS equipment occur occasionally in the field. Mechanical failure has become one of the common failures of GIS. At present, the study of GIS's vibration mostly is analyzing the vibration signal of the shell acquired by the...
Inrush current during the charging of coupling transformer in ±800kV UHV(Ultra high voltage) DC(Direct-Current) converter station, will make the converter AC(Altenative-Current) bus voltage distortion and trigger harmonics in DC system. The harmonics are dominated by the second and the third harmonic. Harmonic will lead to DC voltage, current and power fluctuations, especially DC voltage fluctuation...
Power synchronization control is a new control strategy of VSC-HVDC for connecting a weak power system. This paper reveals that VSC station used power synchronization control normally is dynamically “coupled” with the power system so that the parameters of reactive loop of the VSC-HVDC will make an impact on dynamic interactions and presents the theoretical analysis to explore existence of more strong...
In traditional Power Flow (PF) formulations, the unbalancing power that caused by the transmission power loss (TPL) is provided by sole slack bus, which introduces some errors. Such errors are involved in the results of Continuation Power Flow (CPF) which is based on the parameterized PF formulations. Moreover, for certain class of systems, this kind of errors could be significant and few research...
The earth-mode traveling wave attenuates when propagating along the cable or overhead line and the high-frequency components attenuate faster than the low-frequency components. Therefore, the ratio between the amplitudes of high-frequency component and low-frequency component decreases monotonously as the fault distance increases. Thus, when a constant value is taken for earth modulus velocity, the...
A scheme of restraining transformer inrush current based on control by closing voltage amplitude is proposed based on analyzing the influence factors of transformer inrush current and deriving the mathematical relationship between inrush current and influence factors. In this scheme, in order to making sure that the magnetic flux produced by the transformer no-load closing does not exceed saturated...
Load forecasting is the basis of short-term power system economic dispatch. Currently, the integration of irregular new energy makes the temporal-spatial distribution of nodal load more complicated, and traditional load forecasting is faced with new challenge. In this context, this paper introduces the idea of indirect estimation to the power system nodal load forecasting to deal with the low load...
A real Chinese power grid where a vector controlled unified power flow controller (UPFC) has just been installed is researched in this paper. Firstly, the principle of vector control strategy is presented. Then the linearized model of the power grid is established. Based on the model, damping torque analysis (DTA) method is described. By using the DTA method, the best channel to install the damping...
This paper presents the results of a new program developed for sag-tension calculation in power substations. The different stages of the process are presented and explained in detail. The main advantages of the program are explained and compared with traditional solutions in today's market for sag-tension calculations.
In this paper wavelet packet transform based technique is implemented to discriminate the inrush current from internal fault currents of three phase 240 MVA, 345/38.5 KV star delta connected power transformer. The Daubechies (db4) mother wavelet with two number of level of resolution is found to be optimal in providing information to discriminate the inrush currents from internal fault currents of...
In China, the discrete type transformer has been widely used due to the increasing of underground substation and indoor substation, with constrains of the problem of land occupancy and urban environmental sustainability. This paper proposes a finite element method for studying the thermal model of the discrete type transformer. By solving finite element equations, the temperature field and flow field...
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