The icebreaker is important in the polar scientific investigation and resource exploration. There will be pulse and periodic load during the continuous icebreaking process, which may affect the propulsion system of th...
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The icebreaker is important in the polar scientific investigation and resource exploration. There will be pulse and periodic load during the continuous icebreaking process, which may affect the propulsion system of the icebreaker. This paper mainly analyzes the effect of the impact load on the three-level neutral point clamped (3L-NPC) inverter with diode front-end, and demonstrates the relationship between the impact load and the feedback energy. Moreover, the choice of the resistance of the braking resistor is briefly discussed. The simulation results are given at last, which verify the rationality and correctness of the theoretical analysis.
Aimed at power system large-scale blackouts, the paper firstly analyzes the existing problems of current protective relaying and emergency control in power grid. A novel system protection based on local information, p...
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Aimed at power system large-scale blackouts, the paper firstly analyzes the existing problems of current protective relaying and emergency control in power grid. A novel system protection based on local information, protecting both the equipment and power system secure is then proposed, which scheme consists of: identification of fault flow transferring identification, adaptive overload protection and active load shedding strategy. The processes and system structure are introduced, and the following research points are also discussed in this paper.
Smart substation is the base of smart grid and it is made up of a lot of IEDs (intelligent electric device). Synchronized phasor measurement unit (PMU) plays a very important role in the smart grid, and a great deal o...
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Smart substation is the base of smart grid and it is made up of a lot of IEDs (intelligent electric device). Synchronized phasor measurement unit (PMU) plays a very important role in the smart grid, and a great deal of PMUs have been installed in China. The requirement of PMU in the smart substation is different from traditional substation. This paper introduces that the PMU is suitable for smart substation, there are several details that need to be complemented in IEC 61850 standards, and the paper gives some suggestion to improve it.
The very fast transient overvoltages(VFTO) are generated during operation of disconnect switch (DS) of gas insulated switchgear(GIS). After the opening operation of DS,the load side busbar is left at a residual *** re...
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The very fast transient overvoltages(VFTO) are generated during operation of disconnect switch (DS) of gas insulated switchgear(GIS). After the opening operation of DS,the load side busbar is left at a residual *** residual voltage is determined by the opening phase and the breakdown characteristics of SF6 gap of DS. This study obtains the breakdown characteristic of the test DS,including the dielectric strength recovery speed and polarity effect factor of gap of testing *** the stochastic property of DS opening phase,the opening process of DS is simulated by computer under different dielectric strength recovery speeds and polarity effect *** results show that the dielectric strength recovery speed and polarity effect factor have big influences over the residual *** proper value of dielectric strength recovery speed and polarity effect factor could make the residual voltage minor
In order to study the effect of AC aging on space charge characteristics of low-density polyethylene (LDPE) films, an AC electric field of 50 kV/mm (peak value) was adopted for the accelerated aging test and space cha...
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ISBN:
(纸本)9781538653937
In order to study the effect of AC aging on space charge characteristics of low-density polyethylene (LDPE) films, an AC electric field of 50 kV/mm (peak value) was adopted for the accelerated aging test and space charge measurements of AC aged LDPE films were carried out subsequently. The results show that no significant space charge accumulation in the LDPE samples aged under a 50 kV/mm AC electric field. It can be seen that a significant positive space charge accumulation occurs inside the sample, when DC electric fields were applied to the AC aged LDPE samples. The long-term AC aging also causes more and deeper cracks on the surface of LDPE samples. Moreover, AC aging promotes the oxidation reaction of LDPE. The longer the aging time, the higher the degree of oxidation. On this basis, the probable relationship between space charge characteristics and material physicochemical properties of LDPE during AC electrical aging is clarified.
This paper presents an optimal power flow model for AC/DC meshed networks with modular multi-level converter based HVDC transmission system (MMC-OPF). The MMC-OPF problem is formulated to minimize the total network lo...
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ISBN:
(纸本)9781509054190
This paper presents an optimal power flow model for AC/DC meshed networks with modular multi-level converter based HVDC transmission system (MMC-OPF). The MMC-OPF problem is formulated to minimize the total network loss of the whole AC/DC grids by adjusting generators and converters. In addition, a practical method is proposed to consider N-1 static security constraints with OPF calculation. Case studies of IEEE testing system and a practical network have been carried out. The results demonstrate the effectiveness of the method.
Distributed Energy Resources(DERs) will be an important part of the future power system under the spread of distributed renewable energy generation, electric vehicles, demand response and other technologies. Cyber-phy...
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ISBN:
(数字)9781728196060
ISBN:
(纸本)9781728196077
Distributed Energy Resources(DERs) will be an important part of the future power system under the spread of distributed renewable energy generation, electric vehicles, demand response and other technologies. Cyber-physical system (CPS) is one of the development directions for the future smart grid to integrate the widespread DERs. First, this paper presents the basic architecture and operation process of virtual power plant (VPP). Then the solution of communication structure and software platform are proposed. It is pointed out that virtual power plants have good applicability in information and communication infrastructure, power market and DER integration. Finally, a demonstration program in China is introduced. The research and application of virtual power plant is currently in its embryonic form. It provides a solution for the transmission from centralized power production to the distributed energy utilization, and is an adequate way to integrate geographical dispersion, heterogeneous DERs.
On the basis of analyzing the composition of losses in high-efficient high-voltage asynchronous motors, the approaches of increasing the efficiency of the motors is investigated in this paper. The approaches concern w...
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On the basis of analyzing the composition of losses in high-efficient high-voltage asynchronous motors, the approaches of increasing the efficiency of the motors is investigated in this paper. The approaches concern with the improvement of material, winding, fan, magnetic groove and so on. By taking the economy and efficiency into account synthetically, the design of the YKK series induction motors is carried on, and it is realized by software simulation.
As an advanced internal insulating material, silicone rubber has been widely used in extra high voltage prefabricated cable accessories. However, few studies were focused on the influence of frequency on the electrica...
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As an advanced internal insulating material, silicone rubber has been widely used in extra high voltage prefabricated cable accessories. However, few studies were focused on the influence of frequency on the electrical tree characteristics and the damage mechanism of such insulation is still unknown. In this paper, the characteristics of electrical tree in silicone rubber under AC voltage of different frequency ranging from 50 Hz to 130 kHz were studied. The tree initiation voltage was measured at room-temperature and the processes of electrical tree were observed via a digital micro-observing system. From the experiments, it was found that the electrical tree in silicone rubber is greatly affected by the frequency of applied voltage. With the increase of frequency, tree initiation voltage of silicone rubber decreases. And the frequency can be separated into four stages, while tree initiation voltage appears different magnitude of decrease. There are 3 kinds of electrical tree during the experiments: branch tree, trunk tree and pine tree. The branch tree and pine tree are the primary shapes in the range of low frequency, while the bush tree is the primary shape in the range of HF. The dielectric spectroscopy of silicone rubber was also measured. At last, the influence of frequency on electrical tree in silicone rubber was analyzed. The repeated electro-mechanical stresses applied to the needle tip under high frequency may lead to the decrease of tree initiation voltage of silicone rubber. And with the increase of frequency, the serious erosion in silicone rubber by electrical tree may be caused by the great increase of dielectric losses.
Hydrogen energy, a type of green secondary energy, has attracted much attention in recent years. The production of hydrogen by water electrolysis is less harmful to the environment and makes it possible to obtain hydr...
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Hydrogen energy, a type of green secondary energy, has attracted much attention in recent years. The production of hydrogen by water electrolysis is less harmful to the environment and makes it possible to obtain hydrogen with a high degree of purity. But it requires a lot of electricity and is expensive. Installed capacity and the share of electricity generation from new energy sources have increased recently. The "double high" trend in the power system is becoming apparent. The combination of new energy powergeneration and hydrogen production by water electrolysis can not only promote the absorption of new energy powergeneration, but also reduce the cost of hydrogen production. The conventional thyristor power supply system for hydrogen production has low power factor and poor harmonic performance, which cannot meet the requirements of the new power system. Hydrogen production power supply based on fully controlled devices is gradually becoming mainstream. In this paper, the low voltage ride through capability and the reactive power support function for the power grid of hydrogen production power supply based on fully controlled devices are verified by simulation. For both symmetrical and asymmetrical faults, the hydrogen production power supply can ride through the fault.
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