The smart grid is the next generation power grid, and the smart grid should solve the main problems of the existing power grid, including: 1 Low energy conversion efficiency, only one third of the energy of the existing fuel is converted into electrical energy; 2 The energy loss of the electrical energy transmission is large, about There are 8% of electrical energy loss in the process of electrical energy transfer compared with the existing grid technology, the improvement and improvement of the smart grid include: the generation of electricity from centralized to distributed, the grid structure is transformed from hierarchical to network-based, grid The information is changed from one-way transfer to bi-directional transfer. The fault of the power grid is changed from manual diagnosis to self-diagnosis and self-recovery of the power grid.
As a renewable green energy source, wind energy is of great significance for solving the global energy crisis and reducing carbon emissions. Therefore, wind energy will become an important part of the smart grid characterized by distributed generation. However, the networking problem of wind power is an important issue that needs to be solved in smart grid technology. The bottlenecks are mainly reflected in two aspects: 1 The efficiency and cost issues, reducing costs, increasing efficiency, and increasing the life span have always been the goals pursued by wind turbine development. 1 The structure of the tower 1 generator 1 transformer and the insertion of multi-stage planetary gearboxes not only reduce the efficiency, but also increase the cost, reduce the reliability of the unit, and make the unit extremely bulky and heavy; 2 The wind turbine unit is connected to the grid and The mutual influence between wind turbines and the power grid, wind power output fluctuations, and wind farms far away from the load center, have an adverse impact on the operation of the power grid, so the current power system anti-wind power disturbance capacity is the key to affect the development of wind power industry Sex restrictions.
Prof. Wang Xifan of Xi’an Jiaotong University proposed using the frequency-divided transmission technology to solve the above-mentioned wind power grid connection problem: The frequency-divided wind power system adopts frequency-divided alternating current (such as 50/3Hz) during wind power generation and transmission, and all wind power in the wind farm The machine sends out the same low-frequency electric energy (50/3Hz) through the control system, collects them together through the busbar and boosts it to high voltage, such as over 110kV, and then sends low-frequency electric energy (such as 50/3Hz) to the load center through long-distance transmission. In the area, when the system is fed into the system, AC/AC inverters are used to convert the power into 50Hz power and sent to the load center grid. In this way, the same transmission line can be used to deliver electricity to more distant areas, thus facilitating the connection of wind power to the stronger receiving end system and enhancing the system's anti-disturbance capability, so that the power system can withstand larger wind turbine groups. At the same time, due to the reduced reactance of the frequency-divided transmission system, voltage fluctuations at the power receiving end will be reduced accordingly.
In addition, when the wind turbine emits divided-frequency power, it can greatly reduce the gear box, reduce the gear, improve the unit life, and reduce the cost.
Effect of frequency-divided power transmission on the breaking performance of vacuum circuit breakers The paper discusses the effects of frequency-divided power transmission on the relevant components of wind power systems, including fans, gearboxes, step-up transformers, transmission lines, and AC/AC inverters. However, there is no mention of an important circuit breaker in the system. When the system frequency decreases, the arcing time of the circuit breaker will become longer. For example, at 50Hz, the half-wave of a symmetrical short-circuit current is 10ms, but at 16fHz, a half-wave is 30ms. Longer arcing time will cause a short circuit to various arc extinguishing media and arc extinguishing circuit breakers. Current breaking is difficult, causing the circuit breaker's breaking ability to decrease. The author's goal is to review the effect of split-frequency power transmission on the breaking capacity of vacuum circuit breakers.
For a vacuum circuit breaker designed for operation at 50Hz, how short-circuit current breaking capacity should be when it is running at 16fHz. Related studies indicate that: when the system frequency decreases, the short circuit current of the vacuum circuit breaker breaks. The decrease in capacity is related to the square root of the frequency reduction multiple; taking a transverse magnetic vacuum interrupter as an example, when a short-circuit current is interrupted in a 50Hz system, 8~9ms of the arcing time is a concentrating vacuum arc at the current. There is a 1~2ms diffusion vacuum arc before zero crossing. In the same vacuum interrupter, the arc of the arc in a 16fHz system will have 26~27ms as a condenser vacuum arc before the current passes zero. Although the accumulating vacuum arc rotates rapidly along the edge of the contact under transverse magnetic field driving, under the condition of longer arcing time, the columnar arc will heat the same position of the contact surface more frequently, resulting in overheating of the contact surface. As a result, the density of metal vapor in the current zero zone will be higher, resulting in a decrease in breaking capacity. Assume that: 1 The dielectric recovery strength of the vacuum interrupter after the breaking current is zero is inversely proportional to the metal vapor density of the contact gap; 2 The density of the metal vapor after the current zero crossing is proportional to the arc energy during arcing, and the arc Energy is arc energy =is2=f. Acknowledgments: Professors' suggestions and discussion of this article.
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