Project Snapshot
| Parameter | Value |
| Product | SZ20-31500/35 On-Load Tap-Changing Oil-Immersed Transformer |
| Rated Capacity | 31,500 kVA |
| Project | New Dedicated 35kV Substation — Industrial Production Base |
| Client | Jing Teng Energy Co., Ltd., Alar City, Xinjiang |
| Application | Main transformer for client’s own dedicated substation |
| Project Location | Alar City Industrial Zone, Xinjiang, China |
| Delivery Date | January 12, 2026 |
| Vector Group | YNd11 |
| Cooling Method | ONAN |
| Standards | GB 1094.1/2-2013 · GB 1094.3-2017 · GB/T 6451-2023 · GB 20052-2024 |
Background: A Growing Energy Enterprise Builds Its Own Power Infrastructure
Jing Teng Energy Co., Ltd. is an Alar City-based energy and industrial enterprise engaged in biomass gas production and supply, gas operations, metal materials manufacturing, and engineering management services — operating from its production base in the Alar City Industrial Zone, Xinjiang. With registered capital of RMB 312.5 million and a growing operational footprint, the company reached the scale at which relying on the public distribution network was no longer sufficient for its production needs.
The decision to build a new dedicated 35kV substation at the Alar production base gives Jing Teng Energy direct control over its own power supply — independent voltage regulation, supply continuity, and the ability to manage power quality to the precise standards required by its industrial processes. For an energy production enterprise operating continuous processes, this level of control over power infrastructure is both a practical necessity and a long-term strategic investment.
The main transformer is the defining component of any substation — the unit that steps down the 35kV grid supply to the 10.5kV distribution voltage used throughout the facility, and whose performance characteristics directly determine the quality and stability of power across the entire production base. Jing Teng Energy selected Zhongxin General Electric Energy Co., Ltd. as the main transformer supplier following a technical and commercial evaluation, specifying an on-load tap-changing design capable of continuous voltage regulation without supply interruption.
Why an OLTC Transformer for This Application?
The choice of an on-load tap-changing (OLTC) transformer over a conventional off-circuit tap-changing unit is a deliberate engineering decision suited to continuous industrial operations.
An off-circuit tap changer requires the transformer to be de-energized before the tap position can be adjusted — acceptable for installations where grid voltage is stable and adjustments are only needed during planned maintenance. For an energy production facility running continuous processes, this constraint is operationally unacceptable. Production cannot be interrupted for tap-changing, and grid voltages in western China’s developing industrial zones can fluctuate meaningfully across seasons and load conditions.
The OLTC mechanism allows tap position changes — and therefore output voltage corrections — continuously under full load, without any interruption to supply. The SZ20-31500/35 provides nine tap positions spanning a ±7.5% regulation range around the nominal 35kV input, enabling the substation’s control system to maintain stable 10.5kV output voltage regardless of incoming grid variations.
For Jing Teng Energy’s production base, this means process equipment, gas production systems, and facility infrastructure all receive consistently regulated power — without requiring manual intervention or planned outages for voltage adjustments.
Manufacturing Process: From Core Assembly to Factory Acceptance
At 31,500 kVA and a total weight of 49,320 kg, the SZ20-31500/35 is a substantially larger and more complex unit than a standard distribution transformer. Each manufacturing stage requires more precise engineering, heavier tooling, and more rigorous quality control.
The core is built from grain-oriented silicon steel laminations, stacked in a step-lap configuration that minimizes air gaps between sheets — directly reducing no-load losses. For a transformer that will remain energized continuously for decades, the cumulative energy savings from a well-built core are substantial. Once stacked, the core is secured with steel clamping frames and insulating wooden spacers that mechanically stabilize the lamination stack and maintain electrical isolation between core and structure.
Erecting the completed core from horizontal to vertical requires coordinated use of both a forklift and the workshop overhead crane — a controlled lift demanding careful load management at every stage.
After winding fabrication, the coil assemblies undergo vacuum drying before oil impregnation. This step removes residual moisture from the cellulose insulation system — moisture that would degrade dielectric strength over time and significantly shorten service life. For a unit destined for critical industrial infrastructure, this process step is non-negotiable.
Full Technical Specifications
Core Nameplate Data:
| Parameter | Value |
| Model | SZ20-31500/35 |
| Rated Capacity | 31,500 kVA |
| Rated Frequency | 50 Hz |
| Phases | 3-Phase |
| Vector Group | YNd11 |
| Cooling Method | ONAN |
| Installation | Outdoor |
| Short-Circuit Impedance | 10.5% |
| No-Load Loss | 13,970 W |
| No-Load Current | 0.20% |
| Load Loss | 102,600 W |
| HV Insulation Level | LI200 / AC85 kV |
| LV Insulation Level | LI75 / AC35 kV |
| Insulating Oil Weight | 11,150 kg |
| Core & Winding Weight | 23,500 kg |
| Total Weight | 49,320 kg |
| Tank Vacuum Resistance | 49 kPa |
| Serial No. | A250455 |
| Manufactured | January 2026 |
OLTC Tap Changer Voltage Settings (7-Position On-Load):
| Tap Position | HV Voltage (V) | HV Current (A) | LV Voltage (V) | LV Current (A) |
| 1 | 37,625 | — | — | — |
| 2 | 36,750 | — | — | — |
| 3 | 35,875 | — | — | — |
| 4 (Nominal) | 35,000 | 519.6 | 10,500 | 1,732.1 |
| 5 | 34,125 | — | — | — |
| 6 | 33,250 | — | — | — |
| 7 | 32,375 | — | — | — |
Regulation range: ±7.5% around nominal 35kV, adjustable under full load without supply interruption.
Compliance Standards:
- GB 1094.1/2-2013 — Power transformers: general requirements and temperature rise
- GB 1094.3-2017 — Insulation levels, dielectric tests and external clearances
- GB/T 6451-2023 — Technical parameters for oil-immersed transformers
- GB 20052-2024 — Energy efficiency limits for distribution transformers
Key Components: Engineering for Long-Term Reliability
The OLTC mechanism is the most technically complex component in this transformer. Unlike the simple off-circuit tap selector in a standard distribution transformer, the OLTC must switch between tap connections while carrying full load current — a carefully sequenced make-before-break switching operation inside a dedicated oil compartment, isolated from the main tank oil. The mechanism is designed for tens of thousands of switching operations over its service life, requiring only periodic oil changes and contact inspection.
International Voltage Compatibility
The SZ20-31500/35 is built to China’s GB standard 35kV system voltage. The same OLTC transformer series is available in alternative high-voltage ratings for international substation projects:
| HV Rating | Standard | Primary Markets |
| 33 kV | IEC 60076 / BS 171 | UK, India, Southeast Asia, Sub-Saharan Africa, Middle East |
| 34.5 kV | ANSI / IEEE C57 | USA, Canada, Latin America |
| 35 kV | IEC 60076 / GOST | Continental Europe, Russia, Central Asia |
| 36 kV | IEC 60076 (Um=36kV) | Europe, IEC-compliant international projects |
| 35 kV | GB 1094 | China domestic |
For international projects requiring OLTC transformers at 33kV, 34.5kV, or 36kV, tap changer range, insulation levels, and bushing ratings are all re-specified to match the local grid standard and applicable IEC or ANSI requirements. Contact our engineering team to discuss your project specifications.
Delivery: 49 Tonnes Heading to Xinjiang
With factory acceptance testing complete, the SZ20-31500/35 was prepared for heavy transport to Alar City, Xinjiang — a unit weighing nearly 50 tonnes requiring a specialized vehicle, route pre-survey, and structural loading analysis.
The SZ20-31500/35 departed Zhongxin General’s Sichuan facility on January 12, 2026, bound for Alar City, Xinjiang — a long-haul delivery requiring specialized heavy transport with full pre-departure securing inspection and route planning.
On-Site Installation: From Delivery to Commissioning
On-site installation was carried out by Jing Teng Energy’s own project team at the Alar City Industrial Zone substation site. Following delivery of the transformer main tank, the team proceeded with field assembly of the cooling radiator panels — a standard procedure for large power transformers where radiators are removed for transport to reduce overall dimensions and weight.
The transformer’s ability to be delivered with radiators removed and reassembled on-site by the client’s own team is a practical demonstration of the product’s installation-friendly design and the completeness of Zhongxin General’s technical documentation package — a factor that matters to international buyers evaluating Chinese suppliers.
Project Status: Substation in Operation
As of March 2026 — approximately eight weeks after delivery — the Jing Teng Energy 35kV substation is fully commissioned and in active operation. Real-time CCTV monitoring of the substation confirms the SZ20-31500/35 OLTC transformer is performing in outdoor service, with primary switchgear and secondary protection systems all operational. The substation now provides dedicated, stable power supply to Jing Teng Energy’s Alar City industrial production base as designed.
Related Case Studies
6,300 kVA Oil-Immersed Transformer — Xinjiang Data Center → Standard off-circuit tap-changing transformer for a data center project in Xinjiang Altay. Comparing this project with the SZ20-31500/35 illustrates the key engineering decision between OLTC and off-circuit designs — and when each is the right choice.
63 MVA/110 kV OLTC Transformer — Ningxia LNG & Helium Project → Our largest recent OLTC delivery: a 80-tonne, 110kV transformer for a strategic LNG and high-purity helium production facility. Six months of zero unplanned downtime since commissioning in July 2025.
Intelligent Power Distribution System — Xinjin District People’s Hospital → A 16,730 kVA intelligent power distribution system for a 129,900 m² hospital campus — another mission-critical application where power quality and supply continuity are non-negotiable.
Exporting Dry-Type Transformers to Europe → A first-hand account of navigating EU Commission Regulation 548/2014, CE documentation, and international FAT reporting — the technical refinement process that opened the door to European export markets.
About Zhongxin General Electric Energy Co., Ltd.
Zhongxin General is a Sichuan-based manufacturer of oil-immersed and dry-type power transformers, switchgear, prefabricated substations, microgrids, energy storage systems, and cloud-based power monitoring platforms. The company holds National “Specialized, Refined, Distinctive & Innovative” (Little Giant) Enterprise status — China’s highest SME innovation designation — alongside National High-Tech Enterprise certification and Sichuan Provincial Enterprise Technology Center recognition.
Our transformer portfolio covers 30 kVA to 100 MVA, configurable to voltage classes including 6kV, 6.6kV, 10kV, 10.5kV,11kV, 15kV, 22kV, 33kV, 35kV, 69kV, 110kV, 120kV, and 132kV, in both GB and IEC/ANSI standard configurations for domestic and international projects. with both GB and IEC/ANSI standard variants available for international projects. Strategic cooperation partnerships with State Grid Corporation of China and China Southern Power Grid validate quality management and delivery capability at utility scale.
Planning a Substation or Industrial Power Supply Project?
Whether you need a main transformer for a new dedicated substation, an OLTC unit for a voltage-sensitive industrial application, or a standard distribution transformer for a data center or commercial facility — Zhongxin General’s engineering team can help you define the right specification and execute delivery to your site.
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