This unit is manufactured to GB20052-2024 Tier 1 energy efficiency, China’s highest efficiency grade for power transformers, which is more stringent than the EU’s Ecodesign Regulation No. 548/2014 Tier 1 and Tier 2 loss limits. Lower no-load and load losses translate directly into reduced lifetime energy cost for the end user.
Technical Specifications
| Parameter | Value |
| Type | SZ22-12500/35 |
| Product Code | 1ZX.710.9029 |
| Rated Capacity | 12500 kVA |
| Rated Frequency | 50 Hz |
| Short-circuit Impedance | 7.85 % |
| No-load Loss | 5892 W |
| No-load Current | 0.20 % |
| Load Loss | 50180 W |
| Serial Number | NO.25045 |
| Vacuum Withstand (Tank) | 49 kPa |
| Standard Codes | GB1094.1,2-2013, GB1094.3-2017, GB/T6451-2023, GB20052-2024 |
| Insulation Level | HV Terminals LI 200 AC 85 kV / LV Terminals LI 75 AC 35 kV |
| Number of Phases | 3 Phase |
| Vector Group | YNd11 |
| Service Condition | Outdoor |
| Cooling Method | ONAN (Oil Natural Air Natural) |
| Insulating Oil Weight | 5400 kg |
| Active Part Weight | 11800 kg |
| Total Weight | 22100 kg |
| Date of Manufacture | November 2025 |
On-Load Tap Changer (OLTC) Positions
| Tap Position | HV Voltage (V) | HV Current (A) | LV Voltage (V) | LV Current (A) |
| 1 | 37625 | |||
| 2 | 36750 | |||
| 3 | 35875 | |||
| 4 | 35000 | 206.2 | 10500 | 687.3 |
| 5 | 34125 | |||
| 6 | 33250 | |||
| 7 | 32375 |
At the rated tap position, HV current is 206.2 A and LV current is 687.3 A.
Manufacturing Process
Every SZ22-12500/35 transformer starts with precision core stacking using grain-oriented silicon steel to minimize no-load loss.
The stacked core is then carefully inserted into the pre-formed HV and LV windings, a step that determines the mechanical strength of the unit under short-circuit conditions.
Copper conductors and insulation paper are wound to precise dielectric clearances to meet the rated insulation levels (LI 200 AC 85kV on the HV side).
Quality Control & Testing
Before tanking, every unit undergoes routine factory tests — including insulation resistance, winding resistance, no-load loss, load loss, and induced/applied voltage withstand tests — in line with GB1094.1-2013 and GB1094.3-2017. For background on how we handle stricter export testing requirements, see our case study on exporting dry-type transformers to Europe.
Completed Unit
Once testing passes, the transformer is tanked, oil-filled under vacuum (49 kPa withstand), and finished for dispatch.
The HV and LV porcelain bushings are inspected for creepage distance and sealing integrity before shipment.
The tank top and HV bushing area house the pressure relief and oil conservator connections.
For voltage regulation under load, the unit is equipped with an on-load tap changer offering 7 tap positions from 32,375V to 37,625V — allowing the transformer to compensate for grid voltage fluctuations without interrupting supply. We have delivered similar OLTC transformers for industrial substations, such as this 31,500kVA OLTC transformer project in Xinjiang.
The bottom oil drain valve enables safe oil sampling and maintenance access throughout the transformer’s service life.
Applicable Standards & Testing
Routine tests (every unit): winding resistance measurement; voltage ratio and vector group verification; no-load loss and no-load current; load loss and short-circuit impedance; induced overvoltage withstand test; separate-source AC withstand test; on-load tap changer operation test.
Type tests (reports available on request): temperature rise test; lightning impulse test.
Special tests (available on request): partial discharge measurement; sound level (noise) measurement; short-circuit withstand test.
All tests are conducted to IEC 60076 and GB1094 / GB/T 6451. Factory Acceptance Test (FAT) with client witness is supported. For an example of how we handle stricter client-witnessed testing on export orders, see our case study on exporting dry-type transformers to Europe.
Available Options & Configurations
- Winding material: copper (standard) or aluminium
- Voltage class: HV customizable to match local grid standards
- Frequency: 50 Hz (standard) or 60 Hz
- Energy efficiency grade: GB20052-2024 standard or Tier 1
- Tap changer: on-load (OLTC) as standard on this model, 7 positions
- Conservator sealing: oil-filled (standard) or nitrogen-sealed for long-distance sea freight
- Export wooden crating with full documentation package
Typical Applications
The 12,500 kVA 35kV-class OLTC transformer is specified for dedicated industrial substations, petrochemical and energy processing loads, data center and commercial power infrastructure, and any project requiring stable on-load voltage regulation at this capacity. We have delivered comparable OLTC units for projects such as this 31,500kVA OLTC transformer for Alar Jing Teng Energy, Xinjiang and this 16,000kVA OLTC transformer for an industrial zone substation.
Inquire About 12,500 kVA OLTC Transformer
Need a quotation, technical datasheet, or Factory Acceptance Test arrangement? Tell us your grid voltage, required LV output, frequency, efficiency grade, and installation conditions — and we will configure the right unit for your project.
Contact Us for Price & Datasheet
About Zhongxin General — Oil-Immersed Transformer Manufacturer & Factory
Zhongxin General (Sichuan Zhongxin General Electric Energy Co., Ltd.) is a China-based manufacturer and factory specialising in oil-immersed power transformers and dry-type power transformers, HV/MV/LV switchgear, prefabricated substations, and energy storage systems.
Headquartered in Xinjin District, Chengdu, Sichuan Province, the company holds National “Little Giant” Enterprise status alongside National High-Tech Enterprise certification. Our oil-immersed transformer portfolio covers 30 kVA to 100 MVA, including OLTC configurations at 35kV class and above, in both GB and IEC standard configurations. Every transformer undergoes full routine testing before dispatch, with test reports issued as standard documentation.
Browse our full oil-immersed transformer product range, or explore our case studies and delivery projects to evaluate Zhongxin General as a supplier.
