How to connect photovoltaic transformer to the grid

With the development of global energy structure towards low-carbon and clean, photovoltaic power generation, as an important form of renewable energy, is gradually occupying an important position in the power system. In the construction and operation of photovoltaic power station, the grid-connected technology of photovoltaic transformer is particularly critical, which is directly related to the safe, stable and efficient operation of photovoltaic power generation system.

First, the basic function of photovoltaic transformer

Photovoltaic transformer is the key equipment connecting photovoltaic inverter and power grid. Its main function is to boost the low-voltage alternating current (usually 400V or 315V) output by inverter to a voltage level (such as 10kV, 35kV, etc.) suitable for merging into medium-voltage or high-voltage power grid, so as to reduce the line loss during transmission and meet the technical requirements of power grid access.

Second, the main types of photovoltaic transformers

According to the usage scenarios and structural forms, photovoltaic transformers are usually divided into two types:

1. Box substation (American box substation): integrated transformer, high and low voltage switch and protection device are integrated, which is suitable for distributed photovoltaic system.
2. Combined transformer system (European box transformer): The structure is more complicated, and it is suitable for centralized large-scale photovoltaic power station.

Third, the basic process of photovoltaic transformer grid connection

# 1. Preparation before grid connection
Before the grid-connected operation, the following preparations should be completed:
-Check whether transformers, switch cabinets, protective devices and other equipment have been installed and passed the debugging;
-Confirm that the parameters of the transformer (such as rated voltage, capacity and connection mode) are consistent with the requirements of the power grid;
-Complete relay protection setting and communication debugging of automation system;
-Ensure a good grounding system to avoid electrical safety risks.

# 2. Grid-connected operation steps
The typical grid-connected operation flow of photovoltaic transformer is as follows:
-Step 1: Close the high-voltage side isolating switch and grounding knife switch to confirm that the equipment is in a safe state;
-Step 2: Put the protection device into operation and conduct no-load closing test on the transformer;
-Step 3: Close the low-voltage side switch and connect the inverter output to the transformer;
-Step 4: Step up the voltage step by step, control the output power through the inverter, and observe the changes of voltage and current;
-Step 5: Synchronize with the power grid and realize the matching of voltage, frequency and phase through the automatic synchronization device;
-Step 6: Close the grid-connection switch and officially run in parallel.

# 3. Operation monitoring and protection
After grid connection, the following parameters shall be continuously monitored:
-Voltage, current and frequency;
-Power factor;
-transformer temperature, noise and other operating conditions;
At the same time, perfect relay protection measures, such as over-current protection, quick-break protection and differential protection, should be configured to prevent short circuit and overload from affecting system safety.

Four, grid standards and specifications

In China, photovoltaic grid-connection needs to follow relevant standards such as Technical Regulations for Connecting Photovoltaic Power Stations to Power System (GB/T 19964) to ensure that grid-connection voltage deviation, frequency fluctuation, harmonic content and other indicators meet national regulations. In addition, it also needs to meet the access technical requirements of power grid companies, including reactive power compensation capability and low voltage ride-through capability.

V. Conclusion

As the key equipment connecting photovoltaic power generation system with power grid, the grid-connected process of photovoltaic transformer is not only related to power quality and system stability, but also directly affects the economy and safety of photovoltaic projects. Therefore, in actual operation, we must strictly follow the relevant standards and regulations to ensure that every step of operation is scientific, standardized and safe, and lay a solid foundation for building a green and sustainable energy system.