HUARUI 
Three Dimensional Rolled Core Oil-Immersed Distribution Transformer
The three-dimensional wound core oil-immersed transformer is a high-efficiency and energy-saving power transformer that adopts a three-dimensional wound core structure and uses transformer oil as the cooling and insulating medium. Based on the principle of electromagnetic induction, this product converts electrical energy from the high-voltage side to output at the low-voltage side, achieving voltage transformation and power transmission. The product features complete symmetry of the three-phase magnetic circuit, low no-load loss, low operating noise, and a compact structure. It is suitable for medium and low voltage power distribution scenarios such as urban and rural power grids, industrial and mining enterprises, commercial buildings, and residential areas at voltage levels of 10kV and below, making it an ideal device for achieving energy savings, loss reduction, and green power distribution.
Utilizing three geometrically identical single-frame iron cores arranged at 60° angles to form a three-dimensional equilateral triangle structure, the three-phase magnetic circuits have equal lengths and consistent magnetic reluctance. This results in excellent three-phase balance of no-load current, low harmonic content, and significantly improved power supply quality.
The iron core is made of continuously wound silicon steel sheets without any overlapping joints. The magnetic flux direction is perfectly aligned with the rolling direction of the silicon steel sheets, fully utilizing the material's magnetic conductivity.
The seamless structure eliminates the noise source caused by joint vibration due to magnetostriction. Combined with vacuum annealing to eliminate internal stress, operating noise is reduced by 10-19 dB compared to national standards, approaching silent operation. This makes it particularly suitable for quiet environments such as hospitals, residences, and data centers.
The triangular structure is smaller than traditional oil-immersed transformers of the same capacity, effectively saving installation space in the distribution room and reducing civil engineering investment.
The three-dimensional structure provides evenly distributed heat dissipation channels, ensuring smooth oil circulation and low risk of localized overheating. Its short-term overload capacity surpasses that of traditional oil-immersed transformers, making it suitable for load fluctuation scenarios.
The fully sealed structure design isolates the transformer from air and moisture, preventing oxidation and dampness of the insulating oil. No regular oil sampling or maintenance is required, resulting in a service life of over 30 years.
| Parameter | Value / Range |
| Rated Capacity | 30 kVA – 2500 kVA (customizable) |
| High-Voltage Rating | 6 kV – 11 kV (voltage levels customizable) |
| Low-Voltage Rating | 400 V (customizable upon request) |
| Cooling Method | ONAN (Oil-Immersed Self-Cooled), ONAF (Oil-Immersed Forced-Air-Cooled) |
| Insulation Thermal Class | Class A |
| Impedance Voltage | 4% – 5% (depending on capacity and voltage class) |
| Losses | Compliant with GB 20052, UL, CSA, IEC, DOE 2016, IEEE, ANSI, EN60076, etc.; low-loss optimization available |
| Connection Group | Dyn11, Yyn0, YNd11, Yy0, etc. (optional) |
| Number of Phases | Three-phase |
| Rated Frequency | 50 Hz / 60 Hz |
| Protection Class (IP Code) | IP54 |
| Temperature Rise Limits | Top oil temperature rise ≤ 60 K / Winding maximum temperature rise ≤ 65 K |
| Ambient Temperature Range | –40 °C to +45 °C |
Three-Dimensional Winded Core
Three single-frame cores of identical geometric dimensions are joined at 60° angles to form a three-dimensional triangle. They are continuously wound from silicon steel strip without joints, resulting in a symmetrical magnetic circuit and low no-load loss.
High and Low Voltage Windings
High-quality copper/aluminum conductors are wound and embedded in the core columns to form a rigid structure, providing strong short-circuit resistance and a compact design.
Insulating Oil
Mineral oil, synthetic ester oil, or natural ester oil, serving three main functions: insulation, heat dissipation, and arc extinguishing.
Transformer Tank
A fully sealed, welded steel tank housing the core, windings, and insulating oil. The outer wall features a heat dissipation structure, providing both load-bearing and protective functions.
High/Low Voltage Bushings
Ceramic or composite insulating bushings enable internal and external electrical connections. Insert-type bushings can be selected as needed.
Heat Dissipation Components
Includes corrugated tank walls and plate radiators, utilizing natural oil circulation for heat dissipation, eliminating the need for external fans.
Protective Components
Including gas relays, pressure relief valves, oil thermometers, oil level gauges, tap changers, etc., to achieve pressure regulation, monitoring, and fault protection.
Insulation Components
Insulating paper, insulating boards, insulating pads, etc., to ensure internal electrical clearances and creepage distances.
1. Core Product Advantages
① Significant Energy Saving: The seamless, three-dimensional wound core structure ensures the magnetic flux direction is perfectly aligned with the rolling direction of the silicon steel sheets, resulting in a substantial reduction in no-load losses.
② High-Quality Three-Phase Balanced Power Supply: The three-phase magnetic circuits are perfectly symmetrical, resulting in excellent three-phase balance of no-load current, low harmonic content, stable output voltage, and significantly superior power supply quality compared to traditional stacked core transformers.
③ Low Operating Noise: The seamless structure eliminates joint vibration noise caused by magnetostriction. Combined with vacuum annealing, it operates near-silently, making it suitable for quiet locations such as residential areas and hospitals.
④ Strong Short-Circuit Resistance: The three coils are tightly embedded in the core column to form a rigid whole, effectively resisting the electrodynamic forces generated during sudden short circuits, ensuring high operational reliability.
⑤ Strong Overload Capacity: The three-dimensional structure features uniformly distributed oil circulation channels, high heat dissipation efficiency, low risk of localized overheating, and superior short-term overload capacity compared to traditional oil-immersed transformers. ⑥ Fully Sealed and Maintenance-Free: The fully sealed structure isolates the transformer from air and moisture, preventing oxidation and moisture absorption of the insulating oil. Regular oil sampling is unnecessary, resulting in low maintenance costs.
2. Service Life
The three-dimensional wound core is continuously wound from high-quality cold-rolled grain-oriented silicon steel strip. The seamless structure eliminates magnetic flux distortion and localized overheating problems at the joints of traditional stacked cores, leading to extremely slow magnetic performance decay. The copper/aluminum windings are protected by the insulating oil, preventing oxidation and corrosion. The oil circulation channels are evenly distributed, preventing localized overheating and ensuring uniform aging rates of the winding insulation. The fully sealed structure effectively isolates air and moisture, significantly reducing the oxidation rate of the insulating oil. Under standard operating conditions and proper usage, the overall design service life of the three-dimensional wound core oil-immersed transformer can reach over 30 years.
1. Routine Maintenance
① Check for loose fasteners and terminals: Inspect the tightness of core clamp bolts, winding clamping devices, lead wire connection terminals, and grounding wires. Tighten any loose parts according to the torque standard.
② Test insulation performance and monitor indicators: Regularly measure insulation resistance and dielectric loss factor, monitor the trend of partial discharge changes, and determine if the insulation is damp or aged.
③ Check seals and breather: Check for aging and leakage of the oil tank sealing gasket. Check if the silica gel inside the breather (dehumidifier) has changed color and become ineffective. If more than 2/3 of it is discolored, replace it or dry it.
④ Cooling system inspection: Check for blockages and leaks in the heat sink/radiator. Check if the oil pump and fan are operating normally and without abnormal noises, ensuring smooth oil circulation.
⑤ Protection device testing: Regularly calibrate gas relays (gas relays), pressure relief valves, oil thermometers, oil level gauges, and other protection devices to ensure reliable operation.
2. Safety Regulations
① Power Off and Grounding Verification: Before maintenance, the high and low voltage power supplies to the transformer must be disconnected. After verifying the absence of voltage through voltage testing, a grounding wire should be installed, and a "Do Not Close" warning sign should be hung.
② Wearing Protective Equipment: Workers must be certified and wear insulated shoes, gloves, safety glasses, and work clothes to prevent electric shock and injury from insulating oil.
③ Preventing Insulating Oil Contamination: When inspecting or discharging insulating oil, use a dedicated container to collect it. Random discharge is strictly prohibited to prevent soil and water pollution. Waste oil must be recycled by a qualified unit.
④ Releasing Internal Pressure: Before opening the oil tank inspection port or drain valve, ensure the pressure relief valve is not activated. Release pressure slowly to prevent high-temperature oil vapors from splashing and causing injury.
⑤ Ventilation and Fire Prevention: Maintain good ventilation during indoor maintenance. Open flames are strictly prohibited. Dry powder fire extinguishers should be available on site to prevent insulating oil fires.
⑥ Do not operate with faults: If gas activation, abnormal pressure, serious oil leakage or other faults are found, stop the machine immediately for troubleshooting and do not force the machine to continue operating.
1. Urban and Rural Power Grids: Suitable for the renovation and upgrading of urban and rural power distribution networks, especially suitable for residential areas and commercial streets with high power quality requirements.
2. Industrial and Mining Enterprises: Provides stable power to industrial power equipment and lighting systems in factories, mines, petrochemical plants, etc. Its strong overload capacity can cope with fluctuations in industrial load.
3. Transportation Facilities: Used in power supply systems for subways, airports, stations, etc., ensuring the power safety of transportation.
1. Environmental Risks
1. Insulating Oil Leakage and Pollution Risk: While oil-immersed transformers with wound cores employ a fully sealed structure, prolonged operation can lead to aging and failure of the sealing gaskets, resulting in leakage of mineral insulating oil and contamination of soil and water sources.
2. High-Temperature Overheating Risk: When installed in poorly ventilated locations or under prolonged overload, the top oil temperature may exceed the 95°C limit, accelerating insulating oil oxidation and insulating paper aging, thus reducing equipment lifespan.
3. Low-Temperature Operation Risk: Extremely cold environments (below -25°C) can cause increased viscosity and decreased fluidity of the insulating oil, affecting heat dissipation efficiency and even the flexibility of tap changer operation.
4. Moisture and Corrosion Risk: Outdoor-installed oil-immersed transformers exposed to humid and salt-spray environments (such as coastal areas and chemical industrial zones) are prone to corrosion and rust in the tank, and moisture absorption of the insulation can lead to performance degradation.
5. Fire Risk: Mineral oil is flammable and may cause fires or even explosions in the event of arcing faults or severe overloads. Countermeasures: Configure pressure relief valves, gas relays, and other protective devices; in high-fire-risk locations, use high-ignition-point natural ester oil (ignition point > 300℃) or install automatic fire extinguishing systems.
6. Altitude Impact: At altitudes exceeding 1000m, air density decreases, external insulation strength weakens, and heat dissipation efficiency declines.
2. Installation Restrictions
1. Indoor Installation: For oil volumes ≥ 100kg, a separate transformer room must be provided, equipped with an oil storage tank or oil containment facilities.
2. Fire Separation Distance: ≥ 6m from buildings (civilian); if this requirement is not met, a firewall must be installed, ≥ 0.8m from the exterior wall.
3. Fire Protection Facilities: Must be equipped with an emergency oil tank, a pebble layer (≥ 250mm), a fire extinguishing system, and an oil storage pit.
4. Slope Requirements: When a gas relay is present, the top cover should have a 1%~1.5% slope along the airflow direction.
5. Ventilation Requirements: Primarily natural ventilation; exhaust air temperature ≤ 45℃, intake and exhaust air temperature difference ≤ 15℃.
6. Altitude restrictions: For altitudes above 1000m, external insulation and heat dissipation must be modified, and a high-altitude type should be selected.
This product supports full-dimensional personalization and can be precisely adapted to project conditions, environmental conditions, industry standards, and customer needs. The customization scope is as follows, and the main dimensions are as follows:
| Customization Dimension | Available Options / Description |
| Capacity & Voltage | 30 kVA – 2500 kVA; 6 kV – 11 kV (other voltages available upon request) |
| Connection Group | Dyn11, Yyn0, YNd11, Yy0, ZNyn11, etc. |
| Tap-Changer Type | Off-circuit (de-energized): ±2×2.5% or ±5% / On-load: ±8×1.25%, etc. |
| Cooling Method | ONAN, ONAF, etc. |
| Insulating Fluid Type | Mineral oil (IEC 60296) / Environmentally friendly natural ester oil (FR3, etc.) / Synthetic ester oil |
| Winding Material | All-copper, all-aluminum, HV aluminum / LV copper, copper-aluminum composite, etc. |
| Protection & Corrosion Resistance | IP20 – IP55; Corrosion protection classes C3 / C4 / C5 |
| Installation Environment | Standard outdoor / Outdoor pollution-resistant / Indoor (requires additional protective enclosure) — For harsh conditions such as high temperature, extreme cold, high altitude, high humidity, salt spray, dust, etc., custom-tailored solutions for heat dissipation, insulation, sealing, and anti-corrosion are available. |
| Accessories & Smart Features | Optional add-ons: intelligent temperature control, online oil-level monitoring, remote data transmission, fault alarms, automatic voltage regulation — compatible with unmanned smart grid systems. |
| Applicable Standards | UL / EN 60076 / GB 1094 / IEC 60076 / ANSI C57.12 / CSA / DOE energy-efficiency ratings |
| Color & Labeling | Customer-specified RAL or other color codes; nameplates and warning labels in Chinese, English, or bilingual versions |
