Project Snapshot
| Product | 63 MVA / 110 kV Oil-Immersed OLTC Power Transformer |
| Voltage Ratio | 110 kV / 10.5 kV |
| Vector Group | YNd11 |
| Cooling | ONAN |
| Tap Changer | On-load (OLTC), ±8-step, HV side |
| Voltage Regulation Range | ±10% of nominal grid voltage |
| Total Weight | ~80 tonnes |
| Insulation Level (HV) | LI 480 kV / AC 200 kV |
| Partial Discharge | <50 pC at 1.5× rated voltage |
| Client | Ningxia Helium Technology Co., Ltd. |
| Project Location | Gaoshawo Industrial Park, Yanchi County, Ningxia Autonomous Region |
| Commissioning | July 2025 |
| Operational Status | In service — zero unplanned downtime over six months |
Background: Power for a Continuous-Process Facility
Ningxia Helium Technology Co., Ltd., in strategic partnership with Sany Energy Equipment Co., Ltd., built this facility with a total investment of 520 million RMB. The first phase focuses on two products: liquefied natural gas at 2 million m³/day capacity and high-purity helium at 600,000 m³/year — one of the few domestic helium extraction operations at this scale in China.
Helium is a strategic material. Its applications span semiconductor manufacturing, medical MRI systems, aerospace, and scientific research. Supply constraints and import dependence have made domestic helium production a national priority, which gives this facility an economic and strategic significance beyond its raw production numbers.
The power supply requirement for this application is demanding. High-pressure compression, cryogenic liquefaction, precision decarburisation, and helium separation all run continuously. Any power interruption or sustained voltage instability could compromise product purity, trigger emergency shutdowns, or damage cryogenic equipment. The incoming substation transformer must deliver stable voltage regardless of fluctuations on the 110 kV grid — which is why the client specified an on-load tap-changing design rather than a standard off-circuit unit.
Why OLTC for This Application
An off-circuit tap changer requires the transformer to be de-energised before any tap position change. For a cryogenic gas facility running 24/7, de-energisation is not operationally acceptable. The OLTC mechanism allows tap position changes under full load — the switching sequence happens inside a dedicated oil compartment, isolated from the main tank, with contact transition engineered for tens of thousands of operations over the transformer’s service life.
For the Ningxia facility, this means the substation can compensate for seasonal and diurnal grid voltage variations automatically, without scheduled outages and without dispatching maintenance personnel to the substation.
Manufacturing
The core uses grain-oriented silicon steel laminations in a step-lap configuration — the same approach applied to the 16,000 kVA and 31,500 kVA units documented in other case studies on this site, scaled to the demands of a 63 MVA unit. Step-lap construction minimises air gaps between sheets, directly reducing no-load losses. For a transformer that will remain energised continuously for 30+ years, the cumulative energy saving from a well-built core is substantial.
Winding fabrication uses high-conductivity copper with continuous disk winding technology and vacuum pressure impregnation. Before oil-filling, the entire winding assembly undergoes vacuum drying to remove residual moisture from the cellulose insulation — residual moisture is the primary driver of premature insulation aging in oil-immersed transformers.
Factory Acceptance Testing
Each transformer, especially main transformer, which playes a very critical role in the whole system behind it, undergoes a comprehensive factory acceptance test programme before dispatch:
| Test | Purpose |
|---|---|
| Winding resistance (all tap positions) | Connection integrity and tap changer verification |
| Voltage ratio and phase displacement | Confirm correct transformation and vector group |
| No-load loss and current | Core performance and magnetising characteristics |
| Load loss and short-circuit impedance | Copper loss and impedance at rated current |
| Induced overvoltage / separate source AC | Insulation integrity at above-operating voltages |
| Lightning impulse (480 kV) | Impulse withstand capability of HV insulation system |
| Partial discharge (<50 pC at 1.5× rated) | Internal insulation quality and void detection |
| OLTC mechanical operation (50 cycles min.) | Tap changer reliability and contact performance |
| Dissolved gas analysis baseline | Pre-service DGA reference for condition monitoring |
Transportation
The assembled transformer weighs approximately 80 tonnes. Transport from Zhongxin General’s Chengdu facility to Yanchi County, Ningxia — approximately 1,500 km — required a specialised heavy-transport vehicle, route survey, bridge load assessment, and police escort coordination on restricted sections.
The ONAN cooling radiator panels were removed for transport, reducing overall height and weight to road-legal dimensions. They were packaged separately for on-site reassembly — standard practice for large power transformers.
On-Site Installation and Commissioning
Upon arrival at Gaoshawo Industrial Zone, the Zhongxin General installation team carried out a complete pre-installation inspection — post-transport condition assessment, oil sampling and dielectric testing, and foundation acceptance — before positioning the main unit.
The commissioning sequence followed standard IEC 60076 practice: pre-energisation checks (insulation resistance, winding resistance, turns ratio confirmation, OLTC operation at all 17 positions), initial no-load energisation, staged load application, protection system coordination testing, and performance verification at full load.
Six Months of Operational Performance
Since July 2025, the 63 MVA / 110 kV OLTC transformer has delivered continuous operation supporting the LNG liquefaction and helium extraction processes at Yanchi County. The key performance outcome:
Zero unplanned downtime over six months of continuous operation.
The transformer has operated through Ningxia’s full seasonal range — summer temperatures above 35°C, winter temperatures below -20°C — at approximately 1,500 m altitude, with the dust and sand loading typical of this industrial environment in northwest China.
Representatives from Ningxia Helium Technology confirmed the transformer’s stable voltage regulation has been critical to maintaining helium extraction product purity, where voltage fluctuations affecting cryogenic equipment could directly impact separation quality.
International Standards Compatibility
The SZ22 series OLTC oil-immersed transformer is available in alternative high-voltage ratings for international substation projects:
| HV Rating | Standard | Primary Markets |
|---|---|---|
| 110 kV | IEC 60076 / GB 1094 | China domestic, IEC international markets |
| 115 kV | ANSI / IEEE C57 | USA, Canada, Latin America |
| 132 kV | IEC 60076 | UK, India, Southeast Asia, Middle East |
| 220 kV | IEC 60076 / GB 1094 | China, IEC international markets |
Special environmental specifications — high altitude (above 1,000 m), tropical humidity, seismic zones, extreme cold — are available on request.
Related Case Studies
→ 16,000 kVA OLTC Transformer — Dedicated 35kV Industrial Zone Substation The complete production process from core stacking to dispatch — a smaller OLTC unit in the same product family, showing the manufacturing process in detail.
→ 31,500 kVA OLTC Transformer — Jing Teng Energy 35kV Dedicated Substation Main transformer for a new dedicated industrial substation in Alar City, Xinjiang. Delivered January 2026, confirmed in operation March 2026.
→ Custom Prefabricated Modular Substation — Aktau Port, Kazakhstan A complete substation solution — not just the transformer — for a Belt & Road port project on the Caspian Sea.
→ 8,000 kVA / 120 kV OLTC Transformer — DR Congo Power Station Export International logistics and nitrogen transport for a higher-voltage export project.
About Zhongxin General Electric Energy Co., Ltd.
Zhongxin General is a Sichuan-based National “Little Giant” Enterprise and National High-Tech Enterprise manufacturing oil-immersed and dry-type power transformers (30 kVA to 100 MVA, 0.4 kV to 138 kV), medium-voltage switchgear, prefabricated substations, microgrids, and energy storage systems. The company is a strategic partner of State Grid Corporation of China and China Southern Power Grid.
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