Product Introduction

Solar transformer is a core power equipment designed specifically for solar power generation systems. It converts the low-voltage AC power output by the inverter into medium and high-voltage AC power suitable for grid connection or long-distance transmission, in order to reduce line losses, improve transmission efficiency, and achieve electrical isolation from the power grid, ensuring the safe and stable operation of the system.

Core Functions and Working Principle

The primary function of a solar transformer is voltage boosting. Solar panels generate low-voltage direct current (DC), which is converted to alternating current (AC) by an inverter.

Voltage Boosting: The low voltage direct current (DC) generated by solar panels, typically between 400V and 1000V, is not suitable for long-distance transmission. It is converted into alternating current (AC) of 11kV, 33kV, or even higher through an inverter to meet grid access standards and achieve long-distance, low loss transmission and safe grid connection of electrical energy.
Electrical isolation: achieving physical isolation between the photovoltaic system side (primary side) and the grid side (secondary side), preventing high voltage reverse or fault current backflow in the grid, and protecting the safety of core equipment such as inverters and batteries.
Power quality optimization: Suppress the 3rd, 5th, and 7th harmonics generated by inverters (total harmonic distortion can reach 8% -15%), reduce pollution to the power grid, and ensure that grid connected electricity meets national standards.
System adaptation and stable support: matching the fluctuation characteristics of photovoltaic output, with good overload capacity (able to withstand short-term loads of 110% -120%), adapting to frequent power fluctuations caused by changes in lighting, and ensuring stable operation of the system.
Working principle: The transformer consists of a closed iron core and two insulated windings: the primary winding is connected to a low-voltage power supply, and the secondary winding outputs high-voltage electrical energy.
According to Faraday's law of electromagnetic induction, the voltage can be proportionally increased by adjusting the turns ratio of the primary and secondary windings.
Energy is transmitted through magnetic field coupling without direct electrical connection, achieving dual functions of voltage conversion and electrical isolation.

Mainstream Types and Technical Specifications

When selecting a solar transformer, the type is primarily determined based on the installation environment, capacity requirements, and safety standards:

Type	Key technical parameters and design features	Advantages and disadvantages
Oil immersed transformer	Use mineral oil or natural ester (vegetable oil) for cooling and insulation. Natural esters have a high ignition point (about 360 ° C) and are characterized by biodegradability and high fire safety	Advantages: Strong overload capacity, good heat dissipation, and relatively low cost Disadvantage: There is a risk of oil leakage and regular maintenance is required
Dry type transformer	Insulated with solid materials such as epoxy resin, relying on natural or forced air cooling	Advantages: Fireproof, explosion-proof, environmentally friendly, maintenance free, suitable for installation in residential areas or buildings Disadvantages: High initial cost, large size, and sensitivity to environmental dust
Box-type substation	Integrating transformers, high-voltage switchgear, and low-voltage distribution equipment into outdoor enclosures, commonly used in ground power stations	Compact structure, small footprint, quick installation

Core Challenges and Special Design Strategies

The biggest difference between solar transformers and ordinary power transformers is that they need to deal with the special electrical characteristics of photovoltaic systems:

Dealing with harmonics and high dv/dt: The inverter uses high-frequency pulse width modulation (PWM) technology to output non sinusoidal currents, including high-order harmonics and steep voltage fronts (dv/dt can reach 500V/microsecond), which can easily cause additional eddy current losses and local overheating in the transformer winding, accelerating insulation aging.
Solution: Adopt a special winding structure (such as split winding) and electrostatic shielding layer to filter high-frequency ripples and protect the main insulation.
Dealing with voltage fluctuations and DC components: Photovoltaic power generation is affected by weather, resulting in large output fluctuations and the risk of DC component injection, which may cause transformer core saturation and heating.
Solution: Design a wider voltage regulation range (such as ± 2 × 2.5%) and have a certain DC bias magnetic tolerance.
Dealing with harsh environments: Photovoltaic power stations are often built in extreme environments such as deserts, plateaus, and coastal areas, facing challenges such as high temperatures, sandstorms, salt spray corrosion, and large temperature differences between day and night.
Solution: Improve the protection level (IP54/65), use C5-M anti-corrosion coating, and use insulation materials that are UV resistant and high-temperature resistant.

Summary

Solar transformers are an indispensable link in photovoltaic systems, and they must have three major functions: boosting, isolation, and filtering. Choosing the right transformer not only depends on the capacity and voltage on the nameplate, but also on its ability to optimize harmonic suppression, heat dissipation design, and environmental adaptability. This is crucial for ensuring the power generation revenue of photovoltaic power plants throughout their 25 year lifecycle.

FAQs

Q1: Where is the solar transformer placed in the photovoltaic system? What are the categories?

A: There are mainly two categories:
1.On site step-up transformer: located near the photovoltaic array (box transformer) raise the output of the inverter (0.4kV~0.69kV) to 10kV/35kV;
2.Main transformer of the booster station located in power station collection station, raise the medium voltage inside the station to a higher voltage for grid connection (such as 35kV → 110kV/220kV).

Q2: Why is the protection level required so high for a solar transformer?

A: Solar transformers (especially on-site step-up box transformers) are usually installed outdoors in harsh environments. Coastal areas ≥ IP65, windy and sandy areas ≥ IP54.

Q3:What is the role of solar transformers in suppressing component PID?

A: One effective solution to suppress PID (potential induced decay) is to connect an isolation transformer behind the inverter.

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