1. Photovoltaic power station connected to the grid
1.1 Photovoltaic Power Statio
Photovoltaic power stations in their actual operation process mainly rely on photovoltaic modules to convert solar energy into electricity through a certain form. At this stage, the vast majority of photovoltaic power plants use distributed photovoltaic power generation technology, the main reason is that the technology has a strong environmental compatibility, the application of this technology to the generator set can be matched with the surrounding power users installed. In addition, due to the relatively flexible setting of the construction scale of such a power station, the performance of its components is also required to be relatively high. Although the operating cost of the plant is low during its actual use, its generation cost is slightly higher than its operating cost. Therefore, it can be seen that the power system must further innovate and develop photovoltaic power generation technology, and only in this way can we further promote the wide application of photovoltaic power generation technology.
1.2 Grid-connected structure
In most cases, the distribution network structure in the power system can be divided into three forms: trunk type, ring type and radial type. The application of radial distribution system in these three forms is relatively simple in its practical application process. Because the structure of the radioactive distribution network has many advantages, such as simple wiring, easy protection and adjustment, and relatively convenient expansion. Therefore, this form of distribution network structure is used in many grid-connected photovoltaic power stations.
2. Influence of grid-connected photovoltaic power station on electromechanical protection of distribution network
2.1 Impact on distribution network
From a long-term perspective, the new type of smart grid is the final development trend and development direction of China’s power grid construction. This new access method will certainly have a significant impact on the design and planning of smart distribution networks in the future. From the perspective of the actual construction of the power network, the access of photovoltaic power stations in the power system will further increase the power load in the grid planning. Due to the influence of different transportation conditions, photovoltaic power stations can not provide long-term power energy for the planned area, which makes the distribution network wiring system and distribution network site selection more and more difficult. In most cases, if the distribution network system fails in the process of entering the photovoltaic power station, the fault will seriously affect the operation of low-voltage equipment. Because the relevant power balance will have a certain impact on the frequency stability of the power system, if the photovoltaic capacity is too high, it will also have an adverse impact on the grid frequency. In addition, because the vast majority of grid-connected inverters of photovoltaic power stations at this stage use fair modulation, it is easy to cause harmonic problems, and problems such as oblique wave amplification may occur if the situation is serious. Due to the instability and randomness of photovoltaic power generation in its actual use, it will have a certain negative impact on the waveform and power operation quality of the access area. If the proportion of grid-connected photovoltaic power stations continues to rise, it will interfere with the power grid’s own operating frequency.
2.2 Impact on relay protection of distribution network
First of all, at this stage, with the further development and optimization of solar technology-related levels, many countries are paying more and more attention to the application and construction of solar power generation technology. Due to the relatively small internal capacity of photovoltaic power stations in their actual application process, it is easy to generate problems such as relay protection when it is connected to the distribution network system. Therefore, in the future development process of relay protection, the industry must further regulate and optimize related factors such as the size of the original grid current, so as to effectively reduce the impact of these factors on the electromechanical protection of the distribution network. In addition, in the process of grid-connection of photovoltaic power stations, it is necessary to further optimize the relay protection device of the distribution network, so that it can ensure the safety and reliability of the grid operation to the maximum extent. In the grid-connected management process of photovoltaic power stations, the relevant staff must flexibly apply the effective access policy of photovoltaic power stations, only in this way can the safety and stability of the design and application of the entire distribution network system be effectively improved. In the power system, various grid-connected methods have a differentiated impact on the relay protection of the power grid. Therefore, in the power industry, only by conducting in-depth research and innovation on the power generation advantages of distributed photovoltaic power stations can the relevant staff continuously optimize the systematic design of distribution network relay protection, so as to effectively reduce the negative effect on distribution network relay protection, so that the power network can effectively operate in a safe, stable and efficient state. Secondly, in the distribution network, the most difficult fault problem to solve in the actual operation of photovoltaic power stations is the three-phase short circuit problem, which will also adversely affect the operation of the distribution network. If the photovoltaic system power supply is connected to the grid-connected system power supply in the process of its connection line failure will cause protection action. If the grid-connected grid and photovoltaic power browse are linked together before the automatic reclosing coincides, in this case the photovoltaic power will increase the current in the fault area by continuing to supply power to the fault point, and it will be difficult to extinguish the arc. Because reclosing coincidence will ignite the fault point many times, it is difficult to extinguish. In this case, the temporary fault of the fault point will be transformed into a permanent fault, which will bring great damage to the distribution network system.
3. Improve the specific solutions of grid-connected photovoltaic power stations to the relay protection of the distribution network
3.1 Scientific and rational application of semiconductor materials
As we all know, photovoltaic power stations use solar energy resources to generate electricity. Therefore, from the perspective of photovoltaic power station construction, photovoltaic power stations must have many characteristics such as safety, reliability and application. Photovoltaic power station in its practical application process through the use of semiconductor materials for luminous contact, and through a certain way to convert solar energy into electricity. The use of the photovoltaic effect can be semiconductor photovoltaic contact after the use of advanced science and technology quickly converted into electricity. This technology can effectively use solar energy in a large range, but because of the constraints of the time factor, it has a certain impact on the power generation stability of photovoltaic power stations. Especially when generating electricity at night, almost half of the Earth cannot effectively generate electricity from solar resources. Therefore, photovoltaic power stations and other forms of power generation, such as thermal power generation and hydropower generation, will have a great impact due to the time factor. Although solar energy resources in its practical application process is inexhaustible. However, solar energy resources in the specific application process will be affected by many natural factors and environmental factors. For example, if the photovoltaic power station is in rainy, cloudy weather and other natural conditions, it will seriously restrict the power generation of photovoltaic power stations.
In addition, because the photovoltaic power station is often located in a relatively high level of environmental pollution during its actual use, it will further reduce the visibility in the air, which will also have a certain impact on the efficiency of solar power generation. Therefore, in the process of its practical application, photovoltaic power generation technology can be used in the power system of photovoltaic power stations with more flexible intervention means, so as to carry out a more detailed analysis of the characteristics of the power supply. For example, the high level inverter can be scientifically and reasonably selected according to the actual situation of the photovoltaic power station, so that it can increase the power protection of the conventional distribution network, and further promote the safety and stability of the power system operation.
3.2 Select the voltage level scientifically and reasonably
The different types of motors selected by photovoltaic power stations during their grid-connection can have different effects on the system operation of the entire distribution network. If the photovoltaic power station is located in the surrounding area of the user during the construction process, the electrical energy impact generated within the range of less than 10km can achieve the local impact. In addition, the different forms of power generation of photovoltaic power stations will affect the impact of relay protection devices on the distribution system to a certain extent. If the voltage access of 10kv and below is used, the voltage control network system can be used to further improve the capacity of photovoltaic power stations. In this process, the staff should remember to control the capacity of the photovoltaic power station within 6MV.
3.3 Flexibly select the power grid access mode
There are many kinds of access methods when the photovoltaic power station is connected to the grid. For example, special line access, terminal access and branch access can be used. In the process of grid access, the relevant staff must fully consider the actual application of photovoltaic power stations, so as to scientifically, reasonably and flexibly select access methods, and further strengthen the protection effect of the power supply line. For example, the branch access method can be applied to protect the power line when the fault occurs at the corresponding point, so as to effectively avoid the problem of the fault point affecting the operation quality of the power system.
4. Specific measures to ensure that photovoltaic power stations are connected to the grid to reduce the impact on the relay protection of the distribution network
4.1 Optimization of technical standards
The relevant management workers in the power enterprises must further improve and optimize the standards used in the grid-connected technology of photovoltaic power plants according to the specific situation of photovoltaic power plants. In addition, the specific operator must fully combine the technology, parameters, control, function, operation characteristics of the photovoltaic power station and its related anti-interference characteristics to conduct a comprehensive analysis, on this basis, effectively determine the scale of photovoltaic power station grid-connected installation, photovoltaic power station grid-connected wiring structure and the specific number to be laid.
In addition, the relevant management staff should also set the power quality and voltage level of the photovoltaic power station to be connected to the grid scientifically and reasonably, so as to effectively ensure that the grid-connected work of the photovoltaic power station can be carried out smoothly. At the same time, the relevant management staff should further strengthen the adjustment and optimization of the related electronic equipment such as the reactive power compensation device, so as to greatly improve the standardization and effectiveness of the operation of the photovoltaic power generation system, and reduce the impact on the relay protection system of the distribution network as much as possible.
4.2 Strengthen the monitoring and evaluation of grid-connected operation of power stations
After access to the distribution network, the power enterprise should strictly follow the relevant documents in the power system for the safety of the power network system detection work. And should also be strictly in accordance with the relevant safety management system in the power system to carry out the link and troubleshooting operations for photovoltaic power stations. In the specific operation process, the relevant staff must further increase the detection of the main performance of photovoltaic power stations. For example, relevant staff must conduct strict testing on many issues such as low voltage penetration, power network adaptability and power output characteristics. In addition, the relevant staff must effectively carry out the acceptance and evaluation of power equipment in accordance with the technical requirements and regulations of the technology entering the distribution network. If necessary, it can also carry out the construction of optical power prediction system and the prediction, evaluation and test of power system.
4.3 Further strengthen the research of reactive power compensation
In China’s power industry, the State grid expressly stipulates that the grid-connected field of photovoltaic power plants must further strengthen the research work on reactive power compensation, so as to effectively ensure that the large-scale photovoltaic power plants built in the power industry have the capability of dynamic reactive power compensation.
In addition, we should also conduct in-depth research on the capacity of reactive power equipment, so as to ensure that the grid-connected photovoltaic power station and distribution network system can build a unified reactive power control system in its practical application process, and further strengthen the regulation and management quality of capacitive reactors and reactive power equipment. At the same time, the power industry should also further explore the reactive power regulation capability of photovoltaic power stations, so as to further strengthen the voltage stability of the power distribution network area and effectively improve the transmission and distribution quality of the power system.
5. Conclusion
To sum up, at this stage, because compared with other developed countries, China’s solar power generation started late, so China’s solar power generation technology in photovoltaic power stations is still in the stage of technology research and development and technology improvement. The grid connection of photovoltaic power station has a great impact on the relay protection system of the distribution network. Therefore, only scientific and reasonable management and control can further strengthen the operation safety and operation quality of the distribution network, effectively improve the grid connection level of photovoltaic power station, and then provide a solid foundation for the continuous development and optimization of China’s electric power industry.
