Winding Configuration of Dry-Type Transformers for Grid-Connected PV Power Generation

Dyson

06/25/2025

Solar photovoltaic power generation, a key form of solar energy use, converts sunlight to electricity via solar cells. Free from resource, material, or environmental limits and eco - friendly, it has broad prospects and is a priority renewable energy tech globally. In grid - connected PV systems, transformers (core energy - conversion gear) are essential. Current step - up transformers for PV mainly use 10 kV/35 kV SC - series epoxy - insulated dry - type units, split into two - winding and double - split types. This paper details their selection.

1 Two - Winding Dry - Type Transformers

The structure of two - winding dry - type transformers for PV (as in Figure 1, original reference retained) differs little from traditional distribution dry - type ones in design, process, and manufacturing—core difference is their step - up role. Usually, a single inverter gets a matching two - winding unit based on its rated output and grid voltage.

Given that neutral - point grounding of the dry - type transformer can fail during inverter operation and harmonics exist, their connection group is generally Dy11 to ensure stable equipment running.

2 Double - Split Dry - Type Transformers

In recent years, to limit short - circuit currents and cut capital costs, split transformers (with one winding, usually low - voltage, split into electrically disconnected branches ²) are increasingly adopted. For PV projects, double - split transformers are common: two independent inverter units connect to two branches of the double - split winding, operable independently or together.Considering inverter harmonics, their connection group is usually D, y11y11 or Y, d11d11. Domestically, they’re structurally axial - split or radial - split.

As shown in Figure 2 (original reference), the low - voltage winding has two axially - distributed branches on the same core. Branches have no electrical but magnetic coupling (degree depends on structure ²), and can be segmental or wire - wound. The high - voltage winding has two parallel branches matching the low - voltage ones, with similar specs and total capacity equaling the transformer’s.

2.1 Axial Double - Split Dry - Type Transformers

With a symmetrical structure and uniform leakage flux, it performs well in through/half - through operation. Large impedance between axially - split branches reduces short - circuit currents, ensuring one branch can run if the other fails.

However, its high - voltage winding (two parallel windings) doubles turns but halves conductor cross - section vs conventional. A 35kV D - connected design faces winding production issues (turn control, low efficiency), affecting safety/reliability.

Also, upper/lower low - voltage windings (arranged vertically) have ~20K temperature difference (upper hotter due to air convection). So, design/manufacturing needs enhanced temperature - rise checks and proper insulation selection.

2.2 Radial Double - Split Dry - Type Transformers

Common radial double - split dry - type transformers (structural layout in Fig. 3) have two radially - distributed low - voltage winding branches (usually wire - wound, due to structural specificity) and a single integral high - voltage winding.

The high - voltage winding, with normally - selected turns and conductor cross - section, boasts better winding process/efficiency than axial double - split types. Its near - perfect symmetry ensures good ampere - turn balance in through/half - through operation, plus uniform low - voltage winding temperature rise.

Yet, radially - split low - voltage windings have small division impedance and large coupling capacitance, increasing inter - winding interference. This impacts output power quality and inverter component reliability, requiring adjustments to the inverter - side control loop and system.

2.3 Special Double - Split Dry - Type Transformers

Fig.4 depicts a hybrid design combining axial (segmental/wire - wound low - voltage) and radial (single high - voltage) splits. This hybrid addresses radial low - voltage and axial high - voltage issues, reducing costs and improving manufacturing efficiency.

However, half - through operation (e.g., due to environmental factors or inverter faults) causes severe ampere - turn imbalance, leading to end - winding leakage flux and overheating. This design is thus high - risk.

3 Conclusion

Grid - connected PV transformers primarily use two - winding (step - up, D, y11) or double - split configurations. Key recommendations for double - split designs:

Maintain sufficient low - voltage division impedance for power quality.
Account for axial split temperature differentials in insulation selection.
Use Y, d11d11 for 35kV applications.
Avoid special hybrid designs due to half - through operation risks.

Topics

Solar Transformer Design and Simulation

Dyson

Focused on the design of electrical equipment, proficient in electrical principles and relevant specifications, and skilled in using design software. From intelligent substations to various types of electrical equipment, I am adept at optimizing design solutions, integrating new technologies. With practical experience and collaborative management capabilities, I deliver outstanding electrical design achievements.