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Power Distribution Transformers

Oil-Immersed Distribution & Power Transformers (S11 / S13 / 35kV OLTC)

XBRELE provides a complete range of oil-immersed transformers covering S11 & S13 fully-sealed distribution units (30–2500 kVA) and 35kV OLTC power transformers for substations and heavy-duty industrial networks. Designed for long service life, low losses and reliable outdoor performance.

S11 / S13 Series 10kV / 20kV 35kV OLTC 30–31500 kVA
Oil Immersed Transformer Overview

Reliable Oil Immersed Transformers for Power Distribution & Industrial Applications

Oil Immersed Transformers are essential for a variety of industrial and power distribution applications. XBRELE offers a range of oil-immersed transformers to meet the specific needs of mining, industrial drives, and high-voltage power networks.

Oil Immersed Transformers are built with precision engineering to provide excellent cooling and insulation, ensuring safe and efficient power delivery. Whether it’s for small-scale industrial usage or large-scale power generation, these transformers are built to last and perform under demanding conditions.

For more details on power distribution transformers and specifications, visit our Power Distribution Transformers Pillar Page .

Technical Specifications

Oil-Immersed Transformer Data by Series

Switch between S11, S13 and 35kV OLTC series to review rated capacities, voltage combinations and key loss parameters for power distribution and substation applications.

S11-M 10/20kV Fully Sealed Distribution
S13-M Low-Loss Fully Sealed Distribution
35kV OLTC Oil-Immersed Power Transformers
XBRELE S11-M 10kV fully sealed oil-immersed distribution transformer
S11-M 30–2500kVA fully sealed oil-immersed distribution transformer for 10/0.4kV and 20/0.4kV networks.

S11-M Series — Standard Fully Sealed Distribution Transformers

S11-M oil-immersed transformers adopt hermetically sealed corrugated tanks, high-permeability cold-rolled silicon steel cores and concentric windings. They are widely used in 10kV and 20kV distribution networks with 30–2500kVA ratings.

10 / 20kV 30–2500kVA Fully Sealed Tank Dyn11 / Yyn0

Main Technical Parameters (S11-M Series)

Rated capacity (kVA)High voltage (kV)Tap range (%)Low voltage (kV)Connection groupNo-load loss (W)Load loss (W) Dyn11/Yyn0Impedance voltage (%)No-load current (%)
3010±5 / ±2×2.50.4Dyn11 or Yyn0100600/6304.01.50
5010±5 / ±2×2.50.4Dyn11 or Yyn0130870/9104.01.30
8010±5 / ±2×2.50.4Dyn11 or Yyn01801040/10904.01.20
10010±5 / ±2×2.50.4Dyn11 or Yyn02001250/13104.01.10
12510±5 / ±2×2.50.4Dyn11 or Yyn02401500/15804.01.10
16010±5 / ±2×2.50.4Dyn11 or Yyn02801800/18904.01.00
20010±5 / ±2×2.50.4Dyn11 or Yyn03402200/23104.01.00
25010±5 / ±2×2.50.4Dyn11 or Yyn04002600/27304.00.90
31510±5 / ±2×2.50.4Dyn11 or Yyn04803650/38304.00.90
40010±5 / ±2×2.50.4Dyn11 or Yyn05704300/45204.00.80
50010±5 / ±2×2.50.4Dyn11 or Yyn06805150/54104.00.80
63010±5 / ±2×2.50.4Dyn11 or Yyn081062004.00.60
80010±5 / ±2×2.50.4Dyn11 or Yyn098075004.50.60
100010±5 / ±2×2.50.4Dyn11 or Yyn01150103004.50.60
125010±5 / ±2×2.50.4Dyn11 or Yyn01360120004.50.50
160010±5 / ±2×2.50.4Dyn11 or Yyn01640145004.50.50
200010±5 / ±2×2.50.4Dyn11 or Yyn01940183005.00.40
250010±5 / ±2×2.50.4Dyn11 or Yyn02290212005.00.40
Request S11-M Detailed Datasheet
XBRELE S13-M fully sealed low-loss oil-immersed distribution transformer
S13-M 30–2500kVA low-loss fully sealed oil-immersed distribution transformer for 10kV systems.

S13-M Series — Low-Loss Fully Sealed Distribution Transformers

S13-M transformers upgrade the S11 platform with optimized three-column iron cores and tighter loss limits. Compared with the previous generation, no-load loss is reduced by about 30% and noise is lower, while keeping high short-circuit strength and overload capability.

Low Loss 30–2500kVA 10kV GB / IEC Compliant

Key Technical Parameters & Loss Data (S13-M)

Rated capacity (kVA)High voltage (kV)Tap range (%)Low voltage (kV)Connection groupNo-load loss (W)Load loss (W) Dyn11 / Yyn0Impedance voltage (%)No-load current (%)
3010±5 / ±2×2.50.4Dyn11 / Yyn0100600 / 6304.01.50
5010±5 / ±2×2.50.4Dyn11 / Yyn0130870 / 9104.01.30
8010±5 / ±2×2.50.4Dyn11 / Yyn01801040 / 10904.01.20
10010±5 / ±2×2.50.4Dyn11 / Yyn02001250 / 13104.01.10
12510±5 / ±2×2.50.4Dyn11 / Yyn02401500 / 15804.01.10
16010±5 / ±2×2.50.4Dyn11 / Yyn02801800 / 18904.01.00
20010±5 / ±2×2.50.4Dyn11 / Yyn03402200 / 23104.01.00
25010±5 / ±2×2.50.4Dyn11 / Yyn04002600 / 27304.00.90
31510±5 / ±2×2.50.4Dyn11 / Yyn04803650 / 38304.00.90
40010±5 / ±2×2.50.4Dyn11 / Yyn05704300 / 45204.00.80
50010±5 / ±2×2.50.4Dyn11 / Yyn06805150 / 54104.00.80
63010±5 / ±2×2.50.4Dyn11 / Yyn081062004.00.60
80010±5 / ±2×2.50.4Dyn11 / Yyn098075004.50.60
100010±5 / ±2×2.50.4Dyn11 / Yyn01150103004.50.60
125010±5 / ±2×2.50.4Dyn11 / Yyn01360120004.50.50
160010±5 / ±2×2.50.4Dyn11 / Yyn01640145004.50.50
200010±5 / ±2×2.50.4Dyn11 / Yyn01940183005.00.40
250010±5 / ±2×2.50.4Dyn11 / Yyn02290212005.00.40
Request S13-M Loss Table & Datasheet
XBRELE 35kV double-winding OLTC oil-immersed power transformer for substations
35kV double-winding oil-immersed power transformer with on-load tap changer, rated up to 31500kVA.

35kV Double-Winding OLTC Oil-Immersed Power Transformers

Designed as main step-down units in 35kV substations and industrial power systems, these transformers provide flexible voltage regulation with on-load tap changers and wide capacity coverage from 50kVA up to 31500kVA.

35kV 50–31500kVA On-load Tap Changer Dyn11 / Yd11 / YNd11

Main Technical Parameters — 35kV OLTC Section 50–2500kVA

Rated capacity (kVA)No-load loss (kW)Load loss (kW)No-load current (%)Short-circuit impedance (%)
500.161.20 / 1.14 (Dyn11 / Yyn0)1.36.5
1000.232.01 / 1.911.16.5
1250.272.37 / 2.261.16.5
1600.282.82 / 2.681.06.5
2000.343.32 / 3.161.06.5
2500.403.95 / 3.760.956.5
3150.484.75 / 4.530.956.5
4000.585.74 / 5.470.856.5
5000.686.91 / 6.580.856.5
6300.837.860.656.5
8000.989.400.656.5
10001.1511.50.656.5
12501.4013.90.606.5
16001.6916.60.606.5
20001.9919.70.556.5
25002.3623.20.556.5

Note: Above data for 50–2500kVA section are based on the manufacturer’s standard OLTC design at 35kV / 10.5kV, Dyn11 or Yyn0 connection.

Main Technical Parameters — 35kV OLTC Overall Range 630–31500kVA

ItemParameterTypical value / rangeRemarks
Rated capacitykVA630 – 31500Covers 630, 800, 1000, 1250, 1600, 2000, 2500, 3150, 4000, 5000, 6300, 8000, 10000, 12500, 16000, 20000, 25000, 31500.
High voltagekV35 / 35–38.5Standard 35kV system; some models with extended 35–38.5kV tap range.
Tap range (HV)%±2×2.5 / ±5 / +3 ~ −5On-load tap changer, tap pattern depends on capacity section.
Low voltagekV6.3 / 6.6 / 10.5Typical distribution levels for 35kV/10kV substations and feeders.
Connection group—Dyn11 / Yd11 / YNd11Dyn11 for low-voltage 10.5kV section; Yd11 or YNd11 for higher capacities.
No-load losskW≈ 0.83kW (630kVA) – 21.8kW (31500kVA)See detailed tables in the following high-capacity section or full catalogue.
Load loss (75°C)kW≈ 7.86kW (630kVA) – 115kW (31500kVA)Values vary with capacity and tap position.
No-load current%0.25 – 0.65Typical range from 35kV OLTC transformer parameter tables.
Short-circuit impedance%6.5 / 7.0 / 8.0 / 10.06.5% for small ratings, 7–8% for medium, 10% for 25–31.5MVA section.
Cooling—ONAN / ONAF (for larger ratings)Natural oil-air cooling; forced oil cooling available for high-capacity models.
Measuring & protection—Oil level gauge, oil temperature indicator, gas relay, Buchholz relayAs described in the structural features section of the catalogue.

Main Technical Parameters — 35kV OLTC High-Capacity Section 2000–31500kVA

Rated capacity (kVA)No-load loss (kW)Load loss (kW)No-load current (%)Short-circuit impedance (%)
20002.3019.20.506.5
25002.7220.60.506.5
31503.2324.70.506.5
40003.8729.10.506.5
50004.6434.20.506.5
63005.6336.70.506.5
80007.8740.60.407.0
100009.2848.00.407.0
1250010.956.80.357.0
1600013.170.30.358.0
2000015.382.70.358.0
2500018.397.80.3010.0
3150021.81150.3010.0

Note: High-capacity 35kV OLTC transformers are usually supplied with Yd11 or YNd11 connection, tap ranges ±2×2.5% / ±5%, and cooling type ONAN/ONAF according to project requirements.

Request 35kV OLTC Specification Sheet
Engineered for Reliability

Features of Oil-Immersed Distribution Transformers

XBRELE’s S11/S13/S20 oil-immersed transformers deliver high efficiency, low loss and exceptional durability—ideal for power distribution grids, industrial loads, and substations.

Low Loss

High-Efficiency Core (S11 / S13)

Built with high-grade cold-rolled silicon steel sheets to minimize core loss and improve long-term operating efficiency.

  • Reduced no-load loss: 20–30% lower than older S9 models.
  • Lower noise level: Precision lamination & core structure.
  • Energy-saving design: Meets GB/T 6451 and IEC 60076.
Durability

High-Strength Windings

Copper windings with improved mechanical strength help the transformer withstand short-circuit forces during grid faults.

  • Strong short-circuit endurance: Reinforced with epoxy resin & bracing.
  • Uniform temperature rise: Improves insulation lifespan.
  • Multi-layer structure: Ensures stable electrical performance.
Safe & Reliable

Oil Tank & Cooling System

The robust oil-immersed structure ensures stable cooling and long-term safe operation in outdoor or indoor substations.

  • Corrugated tank: Self-regulating oil expansion.
  • ONAN cooling: Natural air-oil circulation.
  • Enhanced sealing: Prevents leakage and moisture ingress.
Quality Control

Manufacturing & Testing of Oil-Immersed Transformers

From core laminations to final routine tests, every XBRELE oil-immersed transformer follows a controlled process to meet IEC/GB standards for long-term grid operation.

Controlled Manufacturing Process

Each S11 / S13 / S20 transformer is manufactured on a dedicated line, with clear steps from core cutting to vacuum oil filling to ensure low loss and high reliability.

  • 01

    Core Cutting & Stacking

    Cold-rolled silicon steel sheets are sheared and stacked with step-lap joints to reduce no-load loss and noise.

  • 02

    Coil Winding & Insulation

    Copper windings are wound under tension, with layered paper/pressboard insulation to withstand thermal and short-circuit stresses.

  • 03

    Vacuum Drying

    The active part is placed in a vacuum oven to remove moisture from windings and insulation, improving dielectric strength.

  • 04

    Oil Filling Under Vacuum

    Transformer oil is filled under deep vacuum, ensuring no air bubbles remain in the winding and core gaps.

  • 05

    Tank Sealing & Leak Test

    Fully assembled tanks are pressure-tested and checked for leaks before painting and nameplate installation.

QA Standards

Routine & Type Tests

All transformers are tested according to IEC 60076 and GB/T 6451 to verify electrical, mechanical and insulation performance.

Electrical Verification

  • Ratio & polarity test for each tapping position.
  • Impedance & load loss measured at 75 °C.
  • No-load loss & current checked against S11 / S13 tables.
  • Applied & induced voltage tests on HV/LV windings.

Oil & Insulation Control

  • Transformer oil tested for breakdown voltage, water content and dielectric loss factor.
  • Insulation resistance and tan δ measurements on windings.
  • Partial discharge level checked for higher-capacity units.

Mechanical & Appearance

  • Design verified for short-circuit withstand capability.
  • Tank, radiators and fittings inspected for weld quality and coating.
  • Final visual check of nameplate, terminals and accessories before packing.
Test reports can be supplied with each shipment for utility or EPC documentation.
Delivery & Project Support

Reliable Supply Chain for Oil-Immersed Transformers

Whether you need urgent replacements for a transformer in the field or batch delivery for a new power station, XBRELE ensures that your oil-immersed transformers arrive on time and are ready for installation.

Lead Time

Flexible Production

Our manufacturing lines are optimized for quick turnaround of oil-immersed transformers, ensuring your critical installations are met with urgency.

  • Standard Oil-Immersed Transformers: 30–45 days lead time for typical orders.
  • Custom Capacity Orders: 60–90 days depending on transformer rating and customization.
  • Emergency Replacements: Expedited production for urgent replacement needs in power plants.
  • Spare Parts: Key components such as bushings and tap changers are often in stock for quick dispatch.
Packing & Logistics

Heavy-Duty Protection

We understand that shipping transformers requires robust protection. Our packaging ensures your equipment survives long-distance transport safely.

  • Wooden Crating: Fumigated export crates for all heavy transformer units.
  • Moisture Barrier: Vacuum-sealed packaging to prevent corrosion, especially during sea transport.
  • Shock Protection: Reinforced foam and padding to protect delicate transformer bushings.
  • Labeling: Detailed labeling for easy receiving and inventory at project sites.
Engineering Support

Expert Installation & Maintenance Support

Our technical team is always ready to assist with transformer installation and ongoing maintenance requirements.

  • Installation Guidance: We provide guidance on proper installation and connection for optimal performance.
  • Testing & Commissioning: We offer on-site commissioning support to ensure the transformer operates within the required parameters.
  • Maintenance Protocols: Detailed maintenance manuals and recommendations to ensure long-term reliability.
  • Remote Support: Our team can provide remote troubleshooting and support if necessary.
Get a Quote & Lead Time for Oil-Immersed Transformers
FAQ · Oil Immersed Transformers

Common Questions About Oil Immersed Transformers

Here are answers to frequently asked questions about Oil Immersed Transformers, including their benefits, installation, and maintenance.

What is an Oil Immersed Transformer? +
An Oil Immersed Transformer is a type of transformer where the core and windings are submerged in oil. This oil not only provides insulation but also helps cool the transformer during operation. It is widely used in power distribution networks due to its reliability and cost-effectiveness.
What are the advantages of Oil Immersed Transformers? +
Oil Immersed Transformers provide excellent cooling and insulation properties. The oil helps to dissipate heat and maintain optimal operating temperatures. Additionally, the oil provides dielectric strength, preventing short circuits. These transformers are reliable, cost-effective, and have a long service life when maintained properly.
What is the lifespan of an Oil Immersed Transformer? +
The typical lifespan of an Oil Immersed Transformer is between 20 and 40 years, depending on usage, maintenance, and environmental factors. Regular oil testing and maintenance are key to ensuring longevity.
How do I maintain an Oil Immersed Transformer? +
Maintenance of an Oil Immersed Transformer involves checking the oil quality, monitoring the temperature, inspecting the bushings, and testing the tap changer. Regular oil analysis is crucial for detecting moisture, contaminants, or any signs of deterioration. Periodic inspection of the transformer’s mechanical parts is also necessary to ensure optimal operation.
Are Oil Immersed Transformers suitable for outdoor use? +
Yes, Oil Immersed Transformers are designed for both indoor and outdoor use. For outdoor applications, they are usually housed in weatherproof enclosures to protect them from environmental factors like rain, dust, and temperature fluctuations.
Can I use an Oil Immersed Transformer in harsh environments? +
Yes, Oil Immersed Transformers are ideal for use in harsh environments. Specialized models with solid-embedded poles and additional protection are available for use in industries with high pollution, humidity, or extreme temperatures. These models, such as the LZNJ Series, are designed to withstand challenging conditions like those found in cement plants or steel mills.
What testing standards are followed for Oil Immersed Transformers? +
Oil Immersed Transformers are tested according to international standards, such as IEC 60076 and IEEE C57.12.01. These tests include dielectric tests, load losses, temperature rise, and mechanical strength tests to ensure the transformer operates safely and efficiently. For more detailed information, check out the IEC 60076 standards documentation.