Solar PV Power Plant Transformer: Oil Immersed Or Dry Type?

Solar PV Power Plant Transformer: Oil Immersed or Dry Type?

Introduction

To connect a solar PV power plant to the grid, a step‑up transformer is essential. Many customers ask the same question: Should I choose an oil immersed transformer or a dry type transformer?

This article helps you decide from four key perspectives: outdoor environment, voltage level, cost, and maintenance.

1️⃣ Outdoor Environment – Oil Immersed Is More Rugged ️

PV plants are almost always installed outdoors – on wasteland, hillsides, or deserts. Transformers must withstand sun, rain, dust, and salt fog.

• Oil immersed transformer: Fully sealed types reach IP65. The interior is completely isolated from outside air – no problem with dust or moisture. Some models can even survive temporary flooding.

• Dry type transformer: Windings are directly exposed to air. For outdoor use, a metal enclosure is required (adding cost), and dust accumulation over time reduces cooling and insulation performance.

✅ Verdict: For purely outdoor installation, oil immersed is the easier choice.

2️⃣ Voltage Level – 10kV vs 35kV ⚡

Dry type transformers for 35kV are very rare because:

• Higher insulation requirements make them complex, bulky, and expensive

• Price is far higher than oil immersed

✅ Verdict: For 10kV, both are possible. For 35kV, strongly prefer oil immersed.

3️⃣ Cost – Oil Immersed Has Clear Advantages

• Initial purchase cost: For the same capacity, oil immersed is 20–30% cheaper than dry type – a significant saving for PV projects.

• Installation cost: Oil immersed sits directly on a foundation. Dry type needs an extra enclosure, adding civil work and lifting costs.

• Life‑cycle cost: Oil immersed requires oil testing every 3–5 years, but sealed units can run 10+ years without maintenance. Overall, oil immersed is still lower cost than dry type.

✅ Verdict: Oil immersed saves money both upfront and in the long run.

4️⃣ Maintenance – Critical for Remote Plants

PV plants are often in remote areas where maintenance is difficult.

• Oil immersed transformer: Sealed units (especially with natural ester oil) can be 20–30 years maintenance‑free. Just an annual visual check for oil leaks or rust.

• Dry type transformer: Requires regular winding cleaning (vacuum or compressed air). Dust buildup causes partial discharge. In sandy or dusty areas, cleaning may be needed every six months – hard to sustain in remote locations.

✅ Verdict: A fully sealed oil immersed transformer has a lower maintenance burden than a dry type in harsh environments.

Conclusion

For the vast majority of solar PV power plants – especially ground‑mounted large plants – oil immersed transformers are the more mature, economical, and durable choice.

Dry type transformers have their value for rooftop distributed PV, fire‑sensitive locations, and relatively clean indoor environments.

When making your decision, consider:

• Installation location (ground / rooftop / indoor)

• Grid connection voltage (10kV / 35kV / higher)

• Budget

• Maintenance capability

• Local environmental and fire safety regulations

If you are planning a PV project and are not sure which transformer to choose, feel free to contact us. We can provide professional recommendations and a quotation based on your specific capacity, location, and grid connection requirements.