The UHV grid has the characteristics of farther distance and larger capacity than other existing grids. China's energy distribution characteristics determine that China's future large thermal power stations and hydropower stations are almost far from the relevant load centers, and some of the longer distance power transmission features will be more obvious. Whether the power grid can develop healthily is closely related to the development of China's power industry. The following is an analysis of the application of the series compensation and controllable reactors in UHV power grids.
1 series compensation application in UHV power grid
1.1 Planning aspects
Fixed series compensation can effectively reduce the reactance of the circuit, reduce the voltage of the line, reduce the phase difference angle between the voltages at both ends, and continuously improve the dynamic and transient stability margin of the relevant power transmission system. Power transmission creates favorable conditions. Therefore, in the UHV planning process, it is possible to continuously meet the requirements of power transmission by using long-distance line installation series compensation while continuously increasing the transmission corridor.
1.2 Technical problems in series compensation equipment
When the voltage level rises to 1 000 kV, it will affect the relevant equipment, including fiber optic insulators, bypass cutters, bypass breakers and grounding switches. It is necessary for the relevant staff to improve the ground insulation of the series compensation device. Level. Compared to the voltage level of up to 500 kV, the associated rated current in the series-compensated device also increases because of the increase in the rated current of the line. This can affect devices such as capacitors, bypass breakers, etc., and may also result in an increase in MOV capacity.
1.3 Program aspects
In the case of relatively large series compensation capacity, if the vertical voltage is too high, it may bring relatively high pressure on the development and insulation of related equipment. Therefore, it is necessary to divide the string into two sections and then install it on the line. Both ends. After segmentation, the string compensation of a single segment needs to be standardized in terms of parameters. When designing related plans, it is necessary to limit and stipulate the relevant application system conditions in UHV series compensation. In terms of line length and rated voltage of the application system, it is necessary to limit the values ​​and standards, and also consider the line. The reactance in the middle.
2 Application of controllable reactor in UHV power grid
2.1 Application planning aspects
In the process of UHV grid operation planning, in order to effectively suppress the overvoltage, some parallel reactors with relatively high compensation degree are planned and installed, but the relevant power of UHV line planning and transportation is generally limited to a certain limit. The line also needs to meet certain standards, and there is no need for power. Therefore, due to the increase of the voltage level, the line distance of the transmission is prolonged, and the contradiction between the increase of the compensation degree of some high-voltage reactors and the related requirements of the transmission of high power to capacitive reactive power is increasingly prominent. In some long-distance, large-capacity UHV transmission channels, these lines have some similar requirements for controllable reactors. Under such circumstances, the transmission power of the general line is relatively large, and the reactive power demand situation is also obvious. It is also necessary to consider the reactive power compensation of the relevant two-terminal transformer. However, the transformer compensation is limited by the capacity and the capacity of the transformer, and the compensation capability is relatively limited. The result of the phase separation of the reactive partition is not achieved, so the controllable reactor can be considered.
2.2 Equipment selection
According to the current situation, the controllable reactor mainly includes two types, which are high-impedance transformer graded switching type and magnetic valve type. From the research and development difficulty of some UHV controllable reactors, the former is relatively less difficult. If the purpose of the controllable reactor is reactive power balance and voltage regulation, then as long as the relevant classification level and The capacity can meet the requirements of some reactive voltage regulation under various operating conditions. In the initial selection process, some high-impedance transformer-type graded switching machines can be selected. In the future development process, when selecting a controllable reactor, if it is necessary to take into account some dynamic process adjustment, a magnetic valve type controllable reactor is required.
2.3 Controllable reactor
In the development process of some UHV power grids, some long-distance transmission routes have no load demand in the middle. Therefore, it is necessary to establish a Switch station and make a transition. The switch station has no reactive power compensation capability. In such cases, some controllable reactors need to be installed. When installing a controllable reactor, it is necessary to combine the far and near, and consider the transition time of the switch station to expand into a substation. In addition, when considering the installation of series compensation, it is also determined according to the actual work situation.
3 Conclusion
The application of controllable electrical appliances in some UHV power grids can effectively meet some of the relevant pressures for delivering high-power, large-capacity capacitive reactive power and related voltage control, and has sufficient applicability. In addition, in the initial stage of selection, the controllable reactor needs to select some high-impedance transformer hierarchical controllable reactors that are less difficult to develop. In the actual application process, it is necessary to start the project as soon as possible in conjunction with the project.
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