Transformers are indispensable core equipment in commercial and industrial photovoltaic (PV) systems. They not only govern the efficient transmission of PV-generated electricity but also directly affect system stability and safety. This article provides a thorough analysis of the functions, selection principles, common types and characteristics of transformers for C&I PV systems, helping you better understand and apply this key component.
I. Functions of Transformers in C&I PV Systems
In distributed PV power generation systems, transformers are mainly responsible for voltage conversion. After the DC power generated by PV modules is converted to AC power by inverters, transformers step up the voltage to grid voltage levels for grid connection or direct supply to local loads. Proper transformer selection directly impacts power conversion efficiency, equipment investment cost, operation and maintenance difficulty, and overall system reliability.
1. Voltage Conversion
PV panels produce low-voltage DC power, while the grid requires high-voltage AC power. The main role of the transformer is to convert low-voltage DC into high-voltage AC suitable for grid connection. For example, C&I PV stations usually step up voltage to 10 kV or higher for long-distance transmission.
2. Improving Power Generation Efficiency
Optimized transformer design reduces power losses during transmission, thereby improving the overall power generation efficiency of the PV system.
3. Adapting to Complex Environments
C&I PV transformers can operate stably in harsh conditions including high/low temperatures and high humidity, ensuring normal system operation.
4. Ensuring Safety
PV transformers are designed with enhanced fireproof, explosion-proof and moisture-proof performance, which are especially prominent in dry‑type transformers.
II. Transformer Selection Principles for C&I PV Systems
1. Capacity Selection
Transformer capacity should be determined based on the maximum output power of the PV system, system efficiency and load characteristics. A certain margin is usually reserved to improve system reliability and scalability.
2. Voltage Level
Select the appropriate voltage level according to the output voltage of the PV array and grid connection requirements. For instance, small C&I PV systems may connect to the grid at 380 V, while large‑scale systems require 10 kV or higher.
3. Losses and Efficiency
Choose low‑loss, high‑efficiency transformers to minimize energy loss during power transmission.
4. Safety and Maintenance
Consider safety features such as fire and explosion protection, and select easy‑to‑maintain equipment to reduce operating costs.
5. Matching of Rated Voltage
Rated voltage is a fundamental and critical parameter in distributed PV systems. The rated voltages on the high‑voltage and low‑voltage sides of the transformer must match the grid‑connected voltage and the rated AC output voltage of the inverter. This is a prerequisite for smooth grid connection and stable operation.
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Low‑voltage grid‑connected systems:
The high‑voltage side rated voltage is usually the same as the low‑voltage distribution network (e.g., 220 V/380 V). The low‑voltage side rated voltage should match the inverter’s output AC voltage.
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High‑voltage grid‑connected systems:
The high‑voltage side rated voltage can reach 10 kV, 35 kV or higher. Ensure full compatibility with the grid access voltage level to avoid equipment damage or system failures caused by voltage mismatch.
6. Rationality of Rated Capacity
Rated capacity is the key indicator determining the load‑carrying capability. In distributed PV systems, the transformer’s rated capacity should be greater than the total rated capacity of the inverters connected to it. Inverters may generate instantaneous overload or harmonic currents during operation; insufficient transformer capacity can lead to overheating, damage or even fire hazards.
To accommodate future expansion, a capacity margin is recommended. This allows the transformer to support system upgrades without replacement or modification.
7. Transformer Type Selection
Choose the transformer type based on installation environment and application requirements.
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Indoor installation:
Dry‑type transformers are oil‑free, fireproof and explosion‑proof, making them ideal for indoor use. It is recommended to select dry‑type transformers of grade SCB10 or above for energy efficiency and reliability. Pay attention to heat dissipation, noise level and safe distance for maintenance personnel.
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Outdoor installation:
Pad‑mounted transformers integrate the transformer, high‑voltage switchgear and metering equipment in a compact enclosure, suitable for outdoor installation. Focus on protection grade, insulation performance and resistance to harsh environments. For coastal or heavily polluted industrial areas, select transformers with high protection and corrosion resistance.
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Special‑purpose transformers:
Dual‑split transformers are suitable for supplying two loads of different voltage levels simultaneously. Dual‑winding transformers are used for voltage conversion or electrical isolation according to inverter performance requirements.
8. Vector Group Selection
The transformer vector group defines phase relationships and voltage conversion. Select the proper vector group based on grid voltage level and inverter output characteristics.
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Low‑voltage grid‑connected systems:
Ynd11 is commonly used to maintain consistent phase alignment with the low‑voltage distribution network.
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High‑voltage grid‑connected systems:
Dy11 can be used to meet special high‑voltage grid‑connection requirements. Ensure the vector group matches grid specifications and inverter characteristics to avoid faults or equipment damage.
III. Common Types and Characteristics of C&I PV Transformers
1. Oil‑Immersed Transformers
- Features: Large size and heavy weight, but low losses and excellent heat dissipation. Filled with insulating oil, suitable for heavy‑load operation.
- Disadvantages: Risk of leakage and fire; may cause environmental pollution in accidents.
- Applications: Early PV stations; gradually being replaced by dry‑type transformers.
2. Dry‑Type Transformers
- Features: Compact, lightweight, outstanding fireproof, explosion‑proof and moisture‑proof performance; suitable for harsh environments.
- Disadvantages: Relatively higher losses and cost.
- Applications: Modern C&I PV stations, especially those requiring high safety and easy maintenance.
3. Pad‑Mounted Transformers
- Features: High integration, compact design, easy installation; ideal for distributed PV stations.
- Advantages: Uniform internal temperature distribution, which helps improve PV cell conversion efficiency.
- Applications: Rooftop distributed C&I PV stations.
IV. Selection Example Analysis
Suppose a commercial building plans to install a 1 MW distributed PV system connected to the local 10 kV grid.
- Capacity: Considering future expansion, 1.25 MVA or 1.5 MVA is appropriate.
- Type: Located in an urban center with strict fire codes and limited space, a dry‑type transformer is preferred for safety and compactness.
- Efficiency: An amorphous‑alloy dry‑type transformer can be chosen for higher energy efficiency. Although the initial investment is higher, low losses yield significant long‑term economic benefits.
- Protection: Ensure the transformer is equipped with overload protection, short‑circuit protection and temperature/humidity monitoring for safe and stable operation.
V. Summary
Transformers are critical components in C&I PV systems, serving not only for voltage conversion but also improving efficiency, ensuring safety and adapting to complex environments. Proper selection requires comprehensive consideration of capacity, voltage level, losses, safety and maintainability. Currently, dry‑type and pad‑mounted transformers are the preferred choices for C&I PV stations due to their high efficiency and safety.
With the continuous advancement of PV technology, transformer performance will keep improving, providing stronger support for the efficient operation of C&I PV systems.
We hope this article helps you better understand and apply transformers for C&I PV systems and contributes to the development of green energy.
