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Sz-20000-33-11
Yawei
>> Product Introduction
The SZ-20000kVA 33kV/11kV On-Load Tap Changer Power Transformer is a 20MVA step-down unit built to IEC, IEEE, and GB standards. Key features:
✔ Built-in OLTC enables live voltage regulation without load interruption, ensuring stable output under variable grid conditions
✔ Grain-oriented silicon steel core achieves >99% efficiency, reducing no-load losses and operating costs
✔ ONAN/ONAF cooling adapts to load changes, maintaining reliable thermal performance from light to full load
✔ 8% impedance ensures strong short-circuit withstand capability
Suitable for substations, industrial plants, commercial complexes, and renewable energy projects. Designed for 40+ years of service with flexible customization (taps, bushings, protection relays, monitoring systems). Robust construction and premium insulation deliver reliable operation in harsh environments.
Product Advantage
Yawei SZ-20000kVA 33kV/11kV On-Load Tap Changer Power Transformer – Reliable & High-Performance Solution
1. Integrated On-Load Tapping for Uninterrupted Voltage Stabilization
This 20MVA SZ-class transformer delivers dependable 33-kilovolt to 11-kilovolt reduction while incorporating an in-service tap-changing mechanism that enables active output fine-tuning without forcing a supply cut. Core construction utilizes premium textured silicon-steel laminations to constrain standby consumption to ≤18kW and full-load losses to ≤85kW, comfortably satisfying GB/T 6451 and IEC 60076 benchmarks. The resultant 99%-plus efficiency profile translates into around 12% yearly energy-cost mitigation versus legacy counterparts, appealing to utilities and process industries with aggressive operational-expense targets.
2. Dual-Mode Cooling Architecture and Emergency Overload Margin
A hybrid ONAN/ONAF ventilation strategy affords flexible heat expulsion, automatically scaling cooling intensity in response to real-time thermal loading. Rated for uninterrupted operation between -25°C and +50°C external conditions, the assembly additionally tolerates a 20% power excess (120% of nameplate) over two-hour intervals—a critical buffer for grid disturbances or renewable generation intermittency. Infrastructure developers researching online transformer acquisitions will note this model's consistent field durability.
3. Compliance Certification and Short-Circuit Withstand Verification
All design and production phases align with IEC 60076, IEEE C57.12, and GB 1094 frameworks. The transformer presents an 8% reactance value and fortified winding geometries that have successfully endured formal short-circuit proof tests, correlating with a sub-0.2% annual breakdown statistic from installed bases. Its Dyn11 phase relationship facilitates straightforward interfacing with varied distribution architectures, which explains its widespread acceptance among global EPC firms and OEM manufacturing partners.
4. Tailored Feature Sets and Expedited Manufacturing Turnaround
Modification possibilities comprise ±9×1.67% tap adjustment ranges, alternative terminations (ceramic, polymeric, or solid-dielectric bushings), remote surveillance via SCADA-ready instrumentation, C5-M grade protective coatings for saline or chemically aggressive settings, and noise-suppression measures achieving <65dB for urban deployments. With over 150 reference installations internationally, our manufacturing lead time stands at 12 weeks—contact us for a project-specific quotation or to explore engineering adaptations for your particular site demands.
>> Technical Parameters
| Type | Step downpower transformer |
| Model | SZ-20000-33±9×1.67%/11 |
| Cooling Method | ONAN/ONAF |
| Primary Voltage | 33KV |
| Secondary Voltage | 11kV |
| Rated Frequency | 50HZ |
| Rated Power | 20MVA |
| Winding Material | Copper |
| Voltage Regulation | OLTC (On-Load Tap Changer) |
| Tapping Range | ±9×1.67% |
| Connection Group | YNd11 |
| Transformer Dimension | 6800×4500×5300 mm (approx.) |
| Weight | 42000 kg (approx.) |
>> Product Uses
Here are four specific application scenarios of Power Transformer:
1. Utility Substations & Urban Distribution Networks
The SZ-20000kVA 33/11kV power transformer is well-suited for 33kV/11kV primary substations, enabling efficient voltage step-down between transmission-level and medium-voltage distribution networks. With ONAN/ONAF cooling and >99% efficiency, it helps keep grid losses in check even during heavy loading periods. Its 8% short-circuit impedance provides the stiffness needed to maintain stable operation during network disturbances, making it a dependable choice for municipal power authorities and urban infrastructure developments.
2. Renewable Energy Integration (Solar/Wind Farms)
This transformer is frequently deployed in renewable generation projects, stepping up voltage from 11kV collection networks to 33kV for grid interconnection. The built-in OLTC proves particularly valuable here—solar and wind outputs fluctuate constantly, and the tap changer compensates in real time to keep delivery voltage steady. The 120% overload capacity provides a useful buffer for sudden generation spikes, and its robust design holds up well in outdoor farm environments with minimal maintenance intervention.
3. Heavy Industrial Facilities (Mining/Metallurgy)
Heavy industrial operations—steel mills, cement plants, mining sites—often draw large blocks of power at 33kV and need reliable step-down to 11kV for internal distribution. This transformer handles that duty without fuss. The ONAN/ONAF cooling system adapts to the brutal load swings typical of industrial processes, while the OLTC compensates for voltage drops caused by heavy motor starts or arc furnace cycling. The all-copper winding construction and reinforced mechanical bracing ensure it survives repeated short-circuit stresses that would cripple lesser units.
4. Commercial Complexes & Large Mixed-Use Developments
Large shopping centers, hospital campuses, airport facilities, and high-rise office towers increasingly take supply at 33kV to reduce cable losses over long incoming feeders. This transformer steps that down to 11kV for distribution within the site. The low-noise design option (under 65dB) makes it neighbor-friendly in urban settings, and the C5-M corrosion protection package is available for coastal or high-humidity locations. Property developers appreciate the 40+ year design life, which aligns well with long-term asset planning horizons.
>> Product Operate Guide
General installation and operational instructions for 33kV/11kV class power transformers, covering the following sections:
1. Unpacking, Lifting & Jacking
Use designated lifting points and synchronized hydraulic jacks to hoist and level the transformer without tilting or stress damage.
2. Transport, Handling & Site Positioning
Keep the unit upright (tilting ≤15°) during transit and place it on the prepared foundation per layout drawings.
3. Pre-Assembly Inspection & Acceptance
Visually check for damage, oil leaks, and loose parts, and verify all nameplate data and accessories against the packing list.
4. Temporary Storage & Preservation
Store in a dry, ventilated area with nitrogen blanketing (0.01–0.03 MPa) if installation is delayed, and keep auxiliaries in original crates with desiccants.
5. On-Site Reassembly
Install radiators, bushings, conservator, and OLTC mechanism, torque all bolts to specified values, and manually exercise the tap changer through its full range.
6. Vacuum Oil Filling
Pull vacuum below 1 mbar for at least 8 hours after full reassembly, then introduce preheated, degassed oil to the required conservator level.
7. Surface Cleaning & Touch-Up
Clean the tank, apply touch-up paint to scratched areas, and add anti-corrosion coating for coastal or humid environments.
8. Pre-Commissioning Tests
Perform winding resistance, ratio, impedance, insulation, and OLTC transition tests before energization.
9. Commissioning & Energization
Apply rated voltage unloaded for 2–4 hours while monitoring temperature and noise, then gradually step up the load to full rating.
10. Routine Monitoring & Maintenance
Monitor oil temperature, level, and DGA regularly; conduct visual inspections weekly and major overhauls every 10–15 years.
