Analysis on the application of solar photovoltaic system in DC system of substation

Solar energy is the most abundant renewable energy with unique advantages and huge potential for development and utilization. Making full use of solar energy is conducive to maintaining the harmonious coexistence of man and nature and the coordinated development of energy and environment. Since the beginning of the 21st century, the world's solar photovoltaic power generation industry has developed rapidly, and the market application scale has expanded rapidly. Driven by national large-scale engineering projects, promotion plans and international cooperation projects, China's photovoltaic industry is developing rapidly at an unprecedented speed. With the gradual reduction in the price of solar photovoltaic cells, it has become possible to use solar power supply for substations.

2 Application of 110kV Substation Photovoltaic DC System

As a typical unattended substation, the DC load of 110kV substation normally does not exceed 1kW, the battery capacity is 200Ah, the rated voltage and rated current of the DC charger are 220V and 40A respectively, and the trial of the solar photovoltaic DC system 110kV substation is very ideal. The DC system of the substation is an independent solar power generation system. When there is sunshine during the day, the electricity generated by the solar photovoltaic system supplies power to the DC system in the substation, and then connects to the original AC and DC system of the substation. The photovoltaic controller is used to realize automatic power switching when the photovoltaic power generation system generates insufficient power, thereby enhancing the reliability of the DC system power supply. The schematic diagram of the photovoltaic DC system of the substation is shown in Figure 1.

Figure 1. Schematic diagram of the connection of the solar photovoltaic DC system in a substation

3 Characteristics of photovoltaic DC system in substation

On the basis of the original DC system of the substation, solar cell modules and photovoltaic controllers are added. The solar cell module array generates and outputs electric energy under the irradiation of sunlight, and is output to the closing busbar of the DC system after voltage stabilization by the photovoltaic controller. An anti-reverse diode is added to the output circuit of the charger (in fact, an anti-reverse diode has been installed inside the photovoltaic controller and the charging module). In this way, when the output voltage of the solar cell module is within the required range of the DC system, the photovoltaic system supplies power to the DC system and charges the battery at the same time. At this time, the AC contactor at the input end of the charger is disconnected under the control of the photovoltaic controller. When the output voltage of the solar cell module does not meet the required range of the DC system, the photovoltaic controller automatically stops output and controls the AC contactor at the input end of the charger to be attracted. At this time, the charger supplies power to the DC system of the substation. The photovoltaic controller and the charger work alternately and serve as backup for each other to improve the power supply reliability of the DC system of the substation.

4 Configuration of photovoltaic DC system in substation

4.1 Solar cell modules

The battery capacity of the 110kV substation is 200Ah, and the normal charging current limit is 0.1C10 (i.e. 20A). The maximum output power of the solar cell array of the photovoltaic DC system of the substation is required to be 5.1kW. High-quality monocrystalline silicon solar cell modules are used for laying. The area of ​​a single solar cell module is 1.3m2, and 30 modules can be laid within the available area. The maximum power generation of this power generation system can be guaranteed to reach 6kW, which not only meets the needs of battery equalization charging, but also guarantees the power supply to the load.

Table 1 Technical parameters of GCS-165C solar cell modules

4.2 Functions of solar controller

The solar controller adopts a step-by-step current limiting charging method. According to the changing trend of the battery terminal voltage, it automatically controls the connection or disconnection of multiple solar cell arrays in sequence, which can fully utilize the precious solar cell resources and ensure the safe and reliable operation of the battery pack.

4.3 Performance characteristics of solar controller

(1) Photovoltaic cell module input: 1 3+1 lightning arrester; 1 battery input and 1 DC output load each.

(2) Microcomputer control, large-screen LCD display in Chinese, charging and discharging parameters can be set according to the operation of the substation, can adapt to the special requirements of different occasions, and can avoid the charger switch and photovoltaic battery switch being turned on or off at the same time.

(3) With complete protection functions.
(4) With RS-485 or Ethernet communication interface.
(5) With temperature compensation function.
4.4 Controller technical parameters
The technical parameters of the controller are shown in Table 2.
Table 2 Controller technical parameters

4.5 System parameter settings
See Table 3 for system parameter settings.
Table 3 System parameter settings

5 Economic and social benefit analysis
According to calculations, after using the solar photovoltaic system, the substation can save nearly 50,000 kWh of electricity per year, with an economic benefit of 30,000 yuan. Solar energy is a green, environmentally friendly and pollution-free clean energy. Faced with the increasingly tense situation and serious pollution of traditional energy, the use of solar energy is undoubtedly an inevitable trend in the future social development.