When you’re designing or upgrading an industrial facility, the choice of a 35kV power transformer for industrial plant is one of the most critical decisions. This voltage class bridges the utility distribution network (33kV to 35kV) and your plant’s low-voltage switchgear (typically 400V to 690V). A wrong specification can lead to costly downtime, overheating, or even catastrophic failure.
In this guide, we’ll walk through the essential technical parameters, standards, and real-world case studies that procurement managers and electrical engineers need to consider. We’ll also share how FIJ TECH, an experienced transformer manufacturer with 15 years of export expertise, approaches these projects.
Why 35kV Class?
Industrial plants with high load densities—such as steel mills, petrochemical facilities, data centers, and large manufacturing lines—often receive power at 33kV or 35kV to reduce line losses and cable sizes. A dedicated 35kV transformer steps down to a usable low voltage for motors, drives, and lighting.
- Reduces I²R losses on long cable runs
- Allows higher power transfer per feeder (up to 31.5 MVA with custom designs)
- Compatible with common international grid voltages (33kV, 35kV, 36kV class)
- Flexible secondary voltages: 0.4kV, 0.69kV, 3.3kV, 6.6kV, or 11kV
Key Technical Parameters for 35kV Transformers
Before requesting a quote, you must define your load profile, ambient conditions, and installation constraints. Below are the critical parameters that FIJ TECH’s engineers evaluate for every industrial transformer.
Voltage and Capacity Range
| Parameter | Standard Range | Custom Options |
|---|---|---|
| Primary Voltage | 33kV, 35kV | 6kV, 10kV, 11kV, 20kV, 33kV, 35kV |
| Secondary Voltage | 0.4kV (400V) | 0.69kV, 3.3kV, 6.6kV, 11kV |
| Capacity | 2500kVA (standard) | 30kVA to 2500kVA; up to 31500kVA custom |
| Frequency | 50Hz / 60Hz | Both available |
| Cooling | ONAN (oil), AN (dry) | ONAF, AF |
Efficiency and Loss Standards
Energy efficiency is not optional in modern industrial plants. Depending on your target market, you may need to comply with different efficiency benchmarks.
- China: GB 20052-2020 (Grade 1, 2, or 3)
- Europe: EU EcoDesign Tier 2 (for distribution transformers)
- United States: DOE 2016 efficiency regulations
- International: IEC 60076 (power transformers) and IEC 60076-11 (dry-type)
FIJ TECH can design transformers to meet the highest efficiency grade, which often pays back the initial cost within 3-5 years through lower no-load losses.
Dry-Type vs. Oil-Immersed for Industrial Plants
Your installation environment dictates the transformer type. For indoor or fire-sensitive areas, a dry-type transformer is often mandatory. For outdoor or high-power applications, oil-immersed units offer better cooling and lower cost per kVA.
When to Choose Dry-Type (Cast Resin)
- Indoor substations with limited footprint
- Fire safety regulations (no oil containment required)
- High humidity or corrosive atmospheres (with appropriate enclosure)
- Low maintenance requirements
FIJ TECH’s SG(B)13 / SC(B)13 Dry-Type Transformer series covers 35kV class with capacities up to 2500kVA (standard) and custom designs for higher ratings. These units use vacuum-cast resin coils with F-class insulation (155°C) and are available with IP31 or higher enclosures.
When to Choose Oil-Immersed
- Outdoor installations with ample space
- Power ratings above 2500kVA (up to 31500kVA)
- Cost-sensitive projects where oil cooling is more economical
- Existing oil containment infrastructure
Our oil-immersed power transformers are manufactured to IEC 60076 and IEEE C57.12.00 standards, ensuring global acceptance.
Case Study: 35kV Dry-Type Transformer for Middle East Commercial Complex
To illustrate how a 35kV transformer performs in a real-world project, here is a recent FIJ TECH case study.
Project: Commercial Complex in Saudi Arabia
Product: SCB14-2500/35 (35kV/0.4kV, 2500kVA)
Industry: Commercial building (large shopping mall and office tower)
Challenge: The basement substation had limited ceiling height and strict fire safety rules. Oil-filled transformers were not permitted due to the risk of fire spreading.
Solution: FIJ TECH supplied a SCB14 cast resin dry-type transformer with F-class insulation and an IP31 enclosure to protect against dust and accidental contact. The unit was designed to fit the compact basement layout without oil containment pits.
Certifications: The transformer was tested and certified to IEC 60076-11, CE, and ISO 9001:2015, meeting the project’s international specifications.
Customer quote: “The dry type transformer fits our basement substation perfectly. No oil containment needed.” — Facilities Manager, Saudi Arabia
This example shows that a 35kV dry-type transformer can solve logistical and safety challenges that oil units cannot.
Voltage Drop & Short-Circuit Impedance Check
One of the most common engineering oversights is ignoring the transformer’s impedance voltage (uk%) when coordinating with downstream switchgear. Here’s a practical method to verify your design.
- Verify transformer impedance voltage (uk%) matches switchgear breaking capacity. For example, a 10kV distribution transformer typically has uk = 4%. This limits the short-circuit current to about 25 times the rated current, which your switchgear must handle.
- Calculate voltage drop under load: ΔU = β × uk × (cosφ + sinφ × tanθ), where β is the load factor, cosφ is the power factor, and tanθ is the tangent of the load angle.
- Ensure voltage drop at full load stays below 5% at motor terminals. This is critical for induction motors that are sensitive to voltage sags.
For example, if your 35kV/0.4kV transformer has uk = 6% and you run it at 80% load with a power factor of 0.8 (cosφ=0.8, sinφ=0.6), and assuming tanθ = tan(acos(0.8)) = 0.75, the voltage drop would be:
ΔU = 0.8 × 6% × (0.8 + 0.6 × 0.75) = 0.8 × 6% × 1.25 = 6%.
This exceeds the 5% limit, so you might need a transformer with lower impedance (uk=4%) or on-load tap changer (OLTC) to regulate voltage.
FIJ TECH’s engineering team can perform this check for your specific load profile and recommend the optimal uk% and tap range.
Switchgear Integration and Protection
A 35kV transformer is only as reliable as its protection and switching equipment. In many industrial plants, the transformer is fed from a ring main unit or metal-enclosed switchgear.
FIJ TECH also manufactures XGN15-12 AC Metal-Enclosed Ring Network Switchgear, which is suitable for 12kV networks. For 35kV systems, we can supply matching switchgear from our partners or integrate your preferred brand.
Remember to coordinate the transformer’s impedance with the switchgear’s breaking capacity to avoid damage during faults.
Standards and Certifications to Look For
When buying a 35kV transformer for export, ensure the manufacturer holds these certifications:
- ISO 9001:2015 (Quality Management System)
- IEC 60076 (Power Transformers) – covering all parts
- IEC 60076-11 (Dry-Type Transformers) – for resin-insulated units
- IEEE C57.12.00 – for US projects
- GB 1094 – Chinese national standard (often stricter than IEC)
- GB/T 17467 – for compact substations
- CE (European Conformity) – required for EU shipments
- VDE (Germany) – on a project basis
FIJ TECH’s transformers are designed and tested to these standards, and we can provide type test reports upon request.
Why Choose FIJ TECH as Your 35kV Transformer Manufacturer?
With over 15 years of experience in exporting power and distribution transformers, FIJ TECH has built a reputation for reliable performance and responsive engineering support.
- Custom design for unique voltage, frequency, and impedance requirements
- Full range of dry-type and oil-immersed transformers up to 31.5 MVA
- Global compliance: IEC, IEEE, GB, CE, ISO 9001
- Competitive pricing without compromising quality
- On-time delivery with complete documentation
Our engineers work directly with you to confirm the technical specification, perform the necessary calculations, and ensure the transformer integrates seamlessly with your existing switchgear and protection scheme.
How to Get a Quote for Your Industrial Plant
Ready to specify your next 35kV power transformer for industrial plant? Contact FIJ TECH today with your project details: primary and secondary voltages, capacity (kVA), frequency, cooling type, installation environment (indoor/outdoor), and any special standards you need to meet.
Our team will respond within 48 hours with a preliminary technical proposal and budget pricing. We also offer engineering support for transformer selection, voltage drop calculations, and protection coordination.
Visit our product catalog to explore our full range of dry-type transformers and oil-immersed transformers, or browse specific models like the SC(B)13 dry-type transformer and XGN15-12 ring main switchgear.
Let FIJ TECH be your trusted partner for reliable, efficient, and code-compliant power transformation. Request your quote today and experience the difference of working with a manufacturer who understands industrial demands.
For more insights on transformer selection and standards, you can also check our blog posts under transformer-selection and iec-60076.