How to select transformer for photovoltaic power station

With the rapid development of renewable energy, photovoltaic power generation has become an important part of China's energy structure transformation. In the photovoltaic power station system, the transformer is the key equipment to connect the power generation unit with the power grid, and whether its selection is reasonable or not directly affects the operation efficiency, safety and economy of the whole system. Therefore, scientific and reasonable transformer selection is an important link in the design of photovoltaic power plants.

First, the role of transformer in photovoltaic power station

The transformer in photovoltaic power station mainly undertakes the functions of voltage conversion and isolation of power grid. It usually includes step-up transformer (box transformer) and main transformer. Step-up transformer is used to step up the low-voltage alternating current output by photovoltaic module to medium voltage (such as 35kV) to reduce transmission loss; The main transformer further boosts the electric energy to high voltage or ultra-high voltage level (such as 110kV and 220kV), so as to access the public power grid.

Second, the main principles of transformer selection

1. Meet the requirements of electrical parameters
Include rated capacity, voltage ratio, short-circuit impedance, etc. The rated capacity of the transformer should be slightly larger than the maximum output power of the photovoltaic inverter, and certain redundancy should be considered to meet the operation requirements of future expansion or extreme weather conditions.

2. Adapt to the operating environment
Transformers shall be selected according to the climatic conditions (such as temperature and humidity), altitude and dustproof and moistureproof requirements of the installation site. For example, in high temperature and dusty areas, the transformer type with high protection level and good heat dissipation performance should be selected.

3. Consider economy and reliability
We should not only control the initial investment cost, but also take into account the operation and maintenance costs and equipment life. Giving priority to energy-saving transformers, such as amorphous alloy transformers or low-loss silicon steel transformers, is helpful to reduce no-load loss and improve the overall efficiency of the system.

4. Meet the grid-connected standards
The selection of transformer must meet the technical requirements of national and local power grid companies, especially the short-circuit capacity, harmonic suppression ability and other indicators.

Third, the specific steps of transformer selection

1. Determine the installed capacity and grid-connected voltage level.
According to the total installed capacity of photovoltaic power plants (such as 10MW and 20MW) and the grid connection scheme, the required grid-connected voltage level is determined, so as to determine the configuration of main transformer and box transformer.

2. Calculate the load demand
Combined with the actual output power curve of photovoltaic system, the load rate of transformer is calculated to ensure long-term operation without overload and high efficiency.

3. Select the transformer type
Box transformer is often used as step-up transformer in photovoltaic projects because of its compact structure and convenient installation. The main transformer can be oil-immersed or dry-type transformer according to the capacity and voltage level.

4. Check the short circuit and overload capacity
It is necessary to calculate the short-circuit current of the transformer to ensure that it can withstand the surge current when the system fails and ensure the safety of the equipment and system.

5. Consider intelligent configuration
With the development of smart grid, more and more photovoltaic power stations begin to adopt smart transformers with remote monitoring and data acquisition functions to improve the level of operation and maintenance management.

IV. Conclusion

To sum up, the selection of photovoltaic power station transformer is a systematic and comprehensive work, involving electrical, environmental, economic and other aspects. Reasonable selection is not only helpful to improve the operation efficiency, safety and stability of the power station, but also can effectively reduce the operation and maintenance cost and prolong the service life of the equipment. In practical engineering, we should make full investigation and scientific design according to the specific conditions of the project to ensure that the transformer plays its due role in the whole photovoltaic system.