Search

Half wavelength AC transmission (HWACT) is a promising technology with unique advantages in the field of large power transmission over long distance. However, there is little study on the grid connection of HWACT, which shall be an important technical point for its engineering application. This paper deals with the point-to-grid connection of an HWACT line. Firstly, the requirements of grid connection are reviewed, after that the quasi-synchronization is identified for the further study. Then the point-to-grid connection of HWACT under various connection conditions is simulated using PSCAD/EMTDC. The point-to-grid connection characteristics between the HWACT line and the conventional line are compared and analyzed. The simulation results show that when there is only a phase angle error and both the voltage error and the frequency error are zero, the point-to-grid connection characteristics are different. The point-to-grid connection characteristics are the same, provided that there is only a small voltage or frequency error on both sides of the grid-connection switch.

Wind power as the representative of large-scale new energy integration is the main form of China's new energy utilization. However, the risk of subsynchronous oscillation caused by the integration of new energy sources is common in large new energy base. It has become an important problem in the safe and efficient operation of large-scale new energy sources. In this paper, the typical wind power and subsynchronous oscillation are described first, and the initial conditions of device design are extracted. Then, the main circuit design of wind power subsynchronous oscillation suppression device is expounded in detail. The connection reactance, module number and module capacitor are deduced theoretically. A set of applicable main circuit parameters is proposed for typical system requirements. Then, an electromagnetic transient model of subsynchronous oscillation suppression device is built based on PSCAD simulation environment, and the design method of the above parameters is verified. The results show that all the indexes meet the expectations and verify the correctness of the parameter design method.

Half-wavelength AC transmission (HWACT) possessed economic advantages due to its characteristics. However, the problem of secondary arc current limits its development and application. The neutral reactor is not suitable for HWACT and high speed grounding switch (HSGS) has many drawbacks. In this paper, the characteristics of secondary arc current in HWACT are studied in detail. Then, active suppression method for HWACT secondary arc current is proposed, which is based on a converter. Simulation study in PSCAD/EMTDC is carried out to provide its theory feasibility. The simulation results show that the proposed method is able to limit secondary arc current, speed up the arc extinction and improve the system's fault recovery efficiency in HWACT.

Based on the temperature change and thermal storage processes of PCM phase change energy storage unit, the PCM channel number of which is 39, the plate spacing is 0.01 m, the air channel is 40 with its plate spacing of 0.003 m, and the unit length is total of 1.62 m. MATLAB solution about the above PCM energy storage unit was performed according to the model and physical property data, and the numerical simulation was carried out by using Fluent software. The theoretical calculation and numerical simulation were compared and analyzed. It is found that only in the case of smaller or larger flow rate working conditions, the solution results of MATLAB for the increase rate of the average temperature of the phase change material inside the system is quite different from the FLUENT simulation result; the comparison of the phase change process degree of advancement is found that at a higher flow rate, the difference between the two results is small, but the difference is larger when the flow rate is smaller; the comparison result of the PCM liquid rate is different under the small flow rate condition. However, the comparative analysis of heat storage shows that the maximum error does not exceed 10%. It can be seen that the flow rate conditions in the model and working conditions are the obvious factors affecting the two results, but the calculation and simulation results can more accurately describe the heat storage characteristics of the PCM phase change energy storage unit, which was calculated in nearly 90% ranges of working conditions, which can prove that the results of MATLAB and FLUENT are consistent.

After introducing the present operation situation of Tianjin power grid, this paper reveals the causes of the limited transmission capacity of total cross-sectional area and the circuitous power flow of the double lines in Tianjin. The development and state-of-art of static synchronous series compensator (SSSC) technology are covered in this paper along with the lines running plan of Tianjin power grid in future. A variety of measures to deal with the limited section of transmission capacity and roundabout power flow are proposed and compared, which draws to a conclusion that SSSC is the optimal solution for improving power grid structure and adjusting regional power flow. Therefore a detailed application scheme of SSSC is proposed subsequently for the 220kV power grid in Tianjin. The electricity compensation amount of SSSC demands in Tianjin area is analyzed theoretically, and three alternative capacity of SSSC under steady state control are proposed. The optimized capacity and location scheme of SSSC are derived with equivalent data of Tianjin power grid, and are presented in a transmission capacity effect table. Considering the N-1 transient stability limit and the line rated current constraints, the compensation capacity and the capacity curve of the cross section are given, which provides the basis for the SSSC scheme of various operation modes in Tianjin power grid. Finally, the validity and rationality of the SSSC application in Tianjin 220kV power grid are verified via the power flow data of BPA.

Rough test must be done before the TSC (Thyristor switched capacitor) is put into service, to demonstrate the proper design of the valve during over-current conditions, caused by valve firing at instants with non-zero voltage between its terminals. However, modern TSC thyristor valves have a high power rating and are difficult to test directly. The core to design TSC over-current test equipment is to correctly reproduce the stresses on the thyristor under fault conditions. The overcurrent fault conditions of TSC and the corresponding current, voltage and heating stresses on the thyristor valves during over-current are studied. The existing test equipments are appraised. New overcurrent test equipment for TSC valve is proposed. The heating current of the new test equipment is supplied by large current source; the over-current and corresponding reapplied voltage are produced by LC resonant circuit. The schematic diagram of the test equipment is given. The working principles are introduced, and the real test waveforms are analyzed. It is proved that the proposed new over-current test equipment is more flexible, whose test ability is also improved evidently, and the most important is that the new equipment can fully meet the IEC standard so is more equivalence to the real fault, which make it override all the existing TSC over-current test equipment.

In this paper, a novel hybrid filter topology is proposed. It consists of a novel passive filter and an active filter connected in series. The passive filter is composed of a 3/sup rd/- and a 9/sup th/- tuned filter branch and a high-pass filter branch. Each branch includes three star-connected capacitors and an inductor (and an extra resistor in the high-pass branch) connected in series. As the capacitors withstand all the nonzero sequence voltage, the voltage rating of the active filter is reduced substantially. Moreover, there are only zero-sequence fundamental and harmonic currents flowing in the inductors and the active filter, resulting in a reduction of the current ratings. Experimental results from a prototype conform the feasibility of the proposed topology.