Why Oil-Immersed Transformers Are Critical for PV Systems
Oil-immersed transformers provide the thermal stability, environmental resistance, and efficiency required by photovoltaic (PV) systems. Because PV output varies throughout the day due to sunlight changes, transformers must withstand cyclic heating and rapid load fluctuations. Mineral oil and ester oil provide superior cooling performance, ensuring long-term reliability compared with dry-type alternatives.
Heat Resistance for Cyclic PV Loads
PV generation fluctuates from sunrise to sunset. Oil-immersed transformer designs manage cyclic heating more effectively, maintaining stable temperatures under variable inverter load conditions and preventing thermal stress failures.
Outdoor Durability in Harsh PV Environments
ZTELEC CHINA’s oil-immersed transformers are built for demanding environments such as deserts, coastal regions, and high plateaus. They offer strong resistance to dust, moisture, salt fog, UV exposure, and extreme temperature swings.
High Efficiency to Maximize Solar Energy Harvest
Low load and no-load losses help increase the total energy yield of PV systems. This supports the long-term goal of reducing operational costs and improving the return on investment for both utility-scale and commercial PV plants.
ZTELEC CHINA’s Oil-Immersed Transformers in Major PV Applications
ZTELEC’s oil-immersed PV transformers are engineered to meet the operational requirements of different photovoltaic installation types. They provide stable performance, high efficiency, and long-term environmental resistance.
Utility-Scale Ground-Mounted PV Plants (100+ MW)
ZTELEC Solution: S13-M-20000/35 (20,000 kVA, 35 kV)
Why It Works:
ONAF cooling supports continuous high-load operation. Anti-corrosion tank coatings withstand 100 km/h sandstorms, making it suitable for desert solar bases.
Case Study:
ZTELEC provided 60 oil-immersed transformers for a 1.2 GW PV project in Xinjiang, China. Operating efficiency reaches 98.8%, contributing 2.1 TWh of annual clean electricity—enough to supply 500,000 households.
Distributed Commercial & Industrial (C&I) PV (1–50 MW)
ZTELEC Solution: S11-M-1250/10 (1250 kVA, 10 kV)
Why It Works:
Compact dimensions (1.8 m × 1.2 m × 1.5 m) make it ideal for rooftop or indoor transformer rooms. Noise level ≤ 60 dB meets urban industrial noise standards.
Application Example:
A 15 MW rooftop PV system at a Guangdong electronics factory uses 12 ZTELEC units. The installation reduces power costs by 40% and cuts CO₂ emissions by 8,000 tons yearly.
PV + Energy Storage System (PV-ESS) Hybrid Projects
ZTELEC Solution: Custom S13-M-5000/20 with OLTC
Why It Works:
The OLTC enables dynamic voltage control during battery charging and discharging. Reinforced insulation withstands voltage spikes from bi-directional ESS inverters.
Global Project:
ZTELEC supplied 15 transformers for a 75 MW PV + 30 MWh ESS project in Australia. The system stabilizes evening peak supply and reduces grid reliance by 25%.
High-Altitude & Extreme-Temperature PV Plants (≥2,000 m)
ZTELEC Solution: Customized S13-M-3150/10 for altitude adaptation
Why It Works:
2 mm insulation paper compensates for reduced air dielectric strength at high elevations. Automatic oil tank heaters prevent freezing at −5°C or below.
Reliability Record:
Twenty ZTELEC transformers have been operating for six years in a 50 MW PV plant in Tibet—achieving zero downtime even in −25°C winters.
Common Key Specifications of ZTELEC’s Oil-Immersed PV Transformers
ZTELEC’s oil-immersed PV transformers comply with IEC 60076, GB/T 6451 and support customization for voltage levels, cooling methods, environmental protection, and ESS integration. The most-used specifications for mainstream PV applications include 10 kV, 20 kV, and 35 kV configurations.
A complete specification table can be added here based on project requirements.
| Parameter Category | Specification Details | ZTELEC Typical Models & Notes |
|---|---|---|
| Rated Capacity | Distributed PV: 500 kVA – 2.5 MVA
Utility-scale PV: 3.15 MVA – 40 MVA |
S11-M-1250/10 (1250 kVA): For 5-8 MW distributed projects
S13-M-20000/35 (20,000 kVA): For 100+ MW ground plants |
| Voltage Class | LV Side (Inverter Match): 0.4 kV / 1.14 kV
MV Side (Grid Connection): 10 kV / 20 kV / 38 kV |
0.4kV LV: Matches 90% of PV inverters (e.g., 1500V DC inverters)
35kV MV: Standard for utility-scale grids in China/Europe |
| Insulation System | Insulation Class: Class A (≤60K temp rise) / Class B (≤70K temp rise)
Insulating Oil: GB 2536 Mineral Oil (≤15ppm water) / Optional Ester Oil |
ZTELEC uses Kraft insulating paper (high tear resistance) for PV’s cyclic loads
Ester oil option for eco-sensitive areas (e.g., forests) |
| Temperature Limits | Top Oil Temp Rise: ≤55K (above ambient)
Winding Temp Rise: ≤65K (Class A) / ≤75K (Class B) |
Built-in PT100 sensors (ZTELEC patent) for real-time monitoring—vital for desert PV (ambient ≥45°C) |
| Efficiency Class | GB/T 6451 Class 1 (High Efficiency)
No-Load Loss: 3.2 kW (2500 kVA model) Load Loss: 18.5 kW (2500 kVA model) |
S13 series: 0.3-0.5% higher efficiency than Class 2 models—saves 5,000+ kWh/year per unit |
| Short-Circuit Withstand | 10kV Side: 25 kA (2s)
35kV Side: 16 kA (2s) Winding Material: Copper/Aluminum |
Reinforced copper windings (ZTELEC design) resist electromagnetic forces during PV inverter faults |
| Physical Features | Tank Material: Corrosion-resistant Q235 steel
Noise Level: ≤65 dB (1m, 1250 kVA) Cooling Method: ONAN (Natural) / ONAF (Forced Air) |
Anti-sand coating (optional) for desert PV
ONAF cooling for 10+ MVA models (high-load scenarios) |
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