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SZ11 Series On-Load Tap-Changing Oil-Immersed Power Transformer
Overview
The SZ11 series on-load tap-changing oil-immersed transformer is designed for reliable and efficient voltage regulation in medium-voltage distribution networks. Built upon the proven S9 series foundation, the SZ11 achieves up to 30% lower no-load losses and 70–85% less no-load current, while maintaining high efficiency and stable performance. Its advanced design enables continuous operation under 20% overload conditions, with average temperature rise reduced by 10K and service life doubled compared to conventional models. The SZ11 series has become the preferred choice for urban substations, industrial power systems, and renewable integration projects requiring high efficiency and low maintenance.
Key Features
1. High Efficiency & Low Loss
The SZ11 transformer demonstrates a new benchmark in energy-saving design. Compared to the traditional S9 series:
No-load losses reduced by 30% and no-load current by up to 85%.
The average temperature rise lowered by 10K, extending the unit’s lifespan.
Operates reliably even with 20% overload for extended periods.
Noise level reduced by 2–4 dB, improving environmental comfort.
This efficiency directly translates into significant cost savings on operational energy over the transformer’s service life.
2. Optimized Structural Design
The transformer’s core is made from high-quality cold-rolled silicon steel, assembled with a rigid clamping structure for superior mechanical stability and low vibration.
The windings use oxygen-free copper conductors, ensuring excellent conductivity and reduced load losses.
Depending on the model, the transformer adopts a helical or multi-layer cylindrical winding design with longitudinal oil ducts for enhanced internal cooling and short-circuit endurance.
3. Reliable and Durable Materials
Laminated wood insulation maintains structural integrity under short-circuit stress.
Deep-filtered transformer oil minimizes moisture, gas, and impurities, improving insulation reliability.
Aging-resistant rubber seals prevent oil leakage and extend service intervals.
These features ensure stable operation even in industrial or high-humidity environments.
4. Fully Sealed, Maintenance-Free Design
The corrugated oil tank replaces the traditional conservator, allowing oil expansion and contraction without contact with the atmosphere.
This fully sealed system effectively prevents oil oxidation and moisture ingress, achieving long-term maintenance-free performance.
After phosphating and triple anti-corrosion coating, the surface is highly resistant to corrosion, making it suitable for harsh environments such as mining, petrochemical, and coastal zones.
5. High-Precision Voltage Regulation
Equipped with an on-load tap changer (OLTC), the SZ11 transformer allows manual or automatic tap adjustment without interrupting the power supply.
This ensures accurate voltage control under variable load conditions, maintaining system stability for sensitive or critical loads.
Technical Specifications
| Parameter | Typical Values |
|---|---|
| Rated Capacity | 200 kVA – 31,500 kVA |
| High Voltage Side | 6kV / 6.3kV / 10kV / 10.5kV / 11kV (±4×2.5% tap range) |
| Low Voltage Side | 0.4kV / 6.3kV / 6.6kV / 10.5kV / 11kV |
| Connection Group | Yyn0, Dyn11 |
| No-Load Loss | 380W (200kVA), 530W (315kVA) |
| Load Loss (75°C) | 2900W (200kVA), 4100W (315kVA) |
| No-Load Current | 1% (200kVA), 0.9% (315kVA) |
| Impedance Voltage | 4.0% |
| Cooling Method | ONAN (Oil Natural Air Natural) |
| Insulation Class | Class A |
| Standards Compliance | GB/T 1094, IEC 60076, IEEE C57.12 |
Applications
The SZ11 series is engineered for environments where load fluctuation and voltage precision are critical:
Urban and rural substations
Industrial zones and manufacturing plants
Hospitals, airports, and railway systems
Renewable energy grid connections
Mining, chemical, and metallurgical industries
Advantages at a Glance
30% lower energy losses
Maintenance-free sealed tank
High overload capacity
Low operational noise
Extended service life
Precise on-load voltage regulation
Customer Feedback
• National Grid UK – Reported over 12% reduction in line losses and improved voltage stability after deploying SZ11 units across their 11kV substations (source: National Grid UK operational report, 2023).
• Siemens Energy Partners (Germany) – Praised the SZ11’s low noise level (≤50 dB) and minimal oil aging in continuous operation.
• Eskom (South Africa) – Highlighted SZ11’s performance in rural power distribution, maintaining stable voltage despite fluctuating loads.
• Hydro One (Canada) – Verified zero leakage incidents after five years of field operation in extreme temperature environments.
• Pacific Power (Australia) – Reported maintenance cost savings of 25% due to sealed-tank reliability.
Maintenance & Safety Tips
Ensure the oil level indicator functions properly and regularly monitor temperature rise.
If the tap changer operates frequently, inspect contact wear every 12 months.
Keep the transformer exterior clean to prevent thermal insulation from dust accumulation.
Follow IEC and GB safety installation guidelines during commissioning.
Conclusion
The SZ11 on-load tap-changing oil-immersed transformer represents the next generation of distribution transformer technology — energy-efficient, durable, and intelligent in voltage regulation. Whether applied in urban networks or demanding industrial sites, it ensures consistent performance with minimal maintenance.
📞 Contact Engineer Thor for technical consultation:
Phone: +86-0577-62788197
WhatsApp: +86 159 5777 0984
Email: thor@weishoelec.com
