How does distributed photovoltaic power generation affect distribution network protection?
In recent years, distributed photovoltaic power generation has made a leap-like development. The impact of distributed photovoltaic power generation access to the grid and distributed photovoltaic power generation on the distribution network has been highly concerned by friends in the industry.
Due to the unstable output of distributed photovoltaic power generation, the public power grid is required as a backup after accessing the public power grid. With a large number of distributed photovoltaic power generation connected to the power grid, it will have a certain impact on the stability and security of the power grid. What impact will it have on the power grid?
(1) Impact on grid planning. Load forecasting is the basis for the planning and design of the power grid. Whether or not the load can be accurately predicted is a prerequisite for power network planning. The grid-connected photovoltaic power generation has increased the difficulty of load forecasting in its region and changed the existing load growth model. A large number of distributed power accesses make the transformation and management of distribution networks more complex.
(2) The effects of different grid connection methods are different. 1Distributed photovoltaic power generation has no impact on the power grid when off-grid operation; 2 Distributed photovoltaic power generation that is connected to the grid but does not transmit power to the power grid will cause voltage fluctuations; 3 Grid-connected methods that transmit power to the power grid will cause voltage fluctuations. And affect the configuration of relay protection.
(3) Impact on power quality. The important influence of distributed photovoltaic power generation access is to change the voltage distribution on the feeder, and the size of the influence is closely related to the access capacity and access location. Photovoltaic power generation is generally connected to the power grid through inverters. Frequent turning on and off of such power electronic devices can easily generate harmonic pollution.
(4) Impact on relay protection. Most of the distribution networks in China are single-supply radial structures, and they often adopt the form of quick-break, limited-time, quick-break protection and do not have directionality. This kind of protection method can effectively protect all the lines in the existing radial distribution network. However, after the distributed power supply is connected to the distribution network, the injected power will reduce the relay protection range and cannot reliably protect the entire line. Even when other parallel branch faults occur, the relay protection for installing distributed photovoltaic power generation is caused. Misoperation.
Generally, it is accessed through 35kV and below voltage level feeders. When the capacity ratio of the two is large enough, it will affect the short circuit current of the distribution network, and then affect the setting and coordination principle of the protection device. The effect of distributed photovoltaic power generation on the protection of distribution networks is mainly reflected in six aspects:
(1) If the fault occurs upstream of the distributed photovoltaic power generation access feeder, the protective device downstream of the feeder may malfunction;
(b) If the fault occurs in an adjacent feeder, then the feeder may be subject to protective faults;
(3) Connecting the distributed photovoltaic power generation to the distribution network will affect the protection sensitivity of the feeder part. Once the sensitivity changes, it will lead to the occurrence of refusal or misoperation;
(4) The feeder itself has a specific scope of protection. Connecting the distributed photovoltaic power generation to the distribution network will affect the protection scope of the feeder and cause it to change.
(5) When distributed photovoltaic power generation is connected to the substation low-voltage bus, the sensitivity of the current protection of each feeder in the distribution network will be greatly improved. This is because the short-circuit capacity of the system will increase significantly after the low-voltage bus is connected. The corresponding short-circuit current will also increase, so the sensitivity will increase.
(6) After the distributed photovoltaic power generation is connected to the distribution network, once the capacity increases, the protection of the distribution network may be lost.
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