Stable power, superior cooling – oil-immersed distribution transformer, the reliable heart of energy distribution.
01 General
1.1 Project Description
500 kVA oil-immersed distribution transformer was delivered to Australia in 2025. The rated power of the transformer is 500 kVA with KNAN cooling. The high voltage is 11 kV with ±2*2.5% tapping range (NLTC), the low voltage is 0.415 kV, they formed a vector group of YNd11.
Designed for outdoor and exposed environments such as Barrow Island, Western Australia, this unit complies with IEC 60076 and AS/NZS 60076 standards. It is engineered for high ambient temperatures (up to 50°C) and severe environmental conditions, including cyclonic winds (260 km/h) and seismic activity (0.11G).
Key Technical Highlights
1. FR3 Oil (Natural Ester Fluid)
- Type: FR3 natural ester (instead of MIDEL 7131, as offered by the manufacturer)
- Benefits: K-class, high fire point (≥300°C), biodegradable, and environmentally friendly. Supports a fully sealed, gas-free tank design with no conservator or nitrogen cushion.
2. HV Cable Box
- Type: Enclosed, pressurizable cable box with removable connections
- IP Rating: IP56 (dust-tight and protected against powerful water jets)
- Features: Accommodates 11 kV cables, includes bushings for HV neutral termination, and supports bottom entry with load-break elbow terminations (optional).
3. LV Cable Box + Extended Copper Busbars & Supports
- LV Termination: Cable box with extended copper busbars and dedicated busbar supports
- Capacity: Designed for 4 × 240 mm² XLPE/PVC copper cables per phase
- Entry: Bottom or side entry, with a conventional terminal block (not load-break elbows)
4. Terminal Box with Anti-Condensation Heater
- Type: IP56 terminal box with built-in space heater
- Heater Specification: 230 VAC, 50 W (copper)
- Function: Prevents internal condensation, ensuring reliable operation in humid or variable climate conditions.
5. Secondary Wire Contacts (Auxiliary / Alarm / Trip Contacts)
- Winding Temperature Indicator (WTI): Alarm at 110°C, Trip at 130°C
- Oil Temperature Indicator: Alarm & trip contacts
- Pressure Relief Device: Alarm & trip contacts
- Oil Level Gauge: Low oil level alarm
- Control Voltage: All auxiliary contacts rated at 230 VAC
1.2 Technical Specification
500 kVA oil-immersed distribution transformer specifications type and data sheet
| Delivered to | USA |
| Year | 2025 |
| Type | Pad mounted transformer |
| Standard | IEC60076 |
| Rated Power | 500 kVA |
| Frequency | 50HZ |
| Phase | 3 |
| Cooling Type | KNAN |
| Primary Voltage | 11 kV |
| Secondary Voltage | 0.415 kV |
| Winding Material | Copper |
| Vector Group | YNd11 |
| Impedance | 5.75%±7.5% |
| Efficiency | ≥99.16% |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | ≤0.95 kW |
| On Load Loss | ≤5.8 kW |
1.3 Drawings
500 kVA oil-immersed distribution transformer diagram drawing and size.
02 Manufacturing
2.1 Core
| The core uses CRGO silicon steel with a step‑lap construction to minimise hysteresis and eddy current losses. Measured no‑load loss (0.728 kW) and no‑load current (0.60%) are well below the required 0.95 kW and 1.2%, fully matching the specification and complying with IEC 60076. Routine tests confirmed stable thermal performance (HV winding rise 59.25 K ≤ 60 K) and very low noise (46.9 dB(A) vs. 75 dB(A) limit). Quality is ensured by 100% incoming material inspection and online stacking control. The manufacturing highlight is a low‑loss, quiet core that exceeds efficiency requirements. |  |
2.2 Winding
 | Windings are wound from 99.9% electrolytic copper for high conductivity and mechanical strength. Load loss (5.657 kW) and short‑circuit impedance (5.91%) match the required ≤5.8 kW and 5.75% ±7.5%, under IEC 60076. Dielectric tests passed including lightning impulse (75 kV), applied voltage (28 kV HV / 3 kV LV), and induced voltage withstand; temperature rise was 59.25 K for HV and 58.23 K for LV (both ≤60 K). Winding quality is controlled by tension monitoring, 100% turn insulation testing, and vacuum drying before oil filling. The highlight is high short‑circuit withstand capability for harsh outdoor service. |
2.3 Tank
| The fully sealed corrugated steel tank has no conservator or nitrogen cushion and provides IP56 protection. Top oil temperature rise (48.89 K) is within the 55 K limit, and the tank passed a 15 kPa / 24 hour leak test with no leakage, meeting IEC 60076. Quality is assured by controlled welding, 100% kerosene leak detection, and sandblasting before painting. The tank is coated with RAL 7035 polyurethane (minimum 100 μm DFT) for corrosion and UV resistance, making it suitable for high‑salinity environments like Barrow Island. |  |
2.4 Final Assembly
 | The assembled unit integrates all project‑specified features: FR3 environmental natural ester fluid (high fire point ≥300°C, biodegradable, K‑class), a gas‑filled HV cable box with detachable connections, an LV cable box with extended copper bars and supports, a terminal box with an anti‑condensation device (heater/breather), and secondary wiring contacts for monitoring oil temperature, winding temperature and pressure. All accessories match the transformer ratings and comply with IEC 60076 and AS/NZS 60076. Tests confirmed correct operation of the winding temperature indicator (WTI), consistent no‑load tap changer (NLTC) contact resistance, and passed secondary circuit insulation withstand. Quality is ensured through a FAT procedure and pull‑testing of secondary contacts. The manufacturing highlight is modular cable boxes and an anti‑condensation terminal box, ideal for humid, high‑temperature island environments. |
03 Testing
All routine tests were performed per IEC 60076 and witnessed. Key results: no‑load loss 0.728 kW (≤0.95), load loss 5.657 kW (≤5.8), impedance 5.91% (5.75%±7.5%), top oil rise 48.89 K (≤55 K), winding rises 59.25 K / 58.23 K (≤60 K), lightning impulse (75 kV) passed, applied voltage (28/3 kV) passed, sound level ≤46.9 dB(A) (≤75), and 15 kPa/24h leak test passed with no leakage.
04 Packing and Shipping
4.1 Packing
| The transformer is packed on a wooden skid or steel base with a waterproof cover and export‑grade steel strapping. All bushings, cable boxes and the terminal box are fitted with protective caps, and desiccant is placed inside a sealed bag to prevent moisture ingress. Packing complies with export seaworthy requirements (AS/NZS) and includes shock and rust protection. Quality is assured by a final electrical check before packing, photo documentation, and attachment of the complete test report and nameplate drawing. |  |
4.2 Shipping
 | Shipping is done in a 40‑ft open top or flat rack container with the transformer fully assembled. It is secured by bottom bolting, wooden wedges, steel strapping and anti‑skid mats. Positive pressure (dry air or nitrogen) is maintained during transit to avoid moisture ingress. The shipment follows international maritime non‑hazardous regulations (FR3 is K‑class environmental fluid). A shock indicator is attached before departure and inspected upon arrival to ensure no rough handling. |
05 Site And Summary
This 500kVA 11/0.415kV oil‑immersed transformer fully matches the project technical specification. It incorporates FR3 environmental oil, HV and LV cable boxes (the latter with extended copper bars and supports), an anti‑condensation terminal box, and secondary wiring contacts. All parameters are compliant with IEC 60076 and AS/NZS 60076. Reliability is proven by the routine test report: losses lower than guaranteed, ample temperature rise margins, all dielectric and impulse tests passed, leak‑tight, and very low noise. Quality is assured by an ISO 9001 traceable manufacturing process. With its hermetically sealed corrugated tank, IP56 protection and features for humid/salty environments, this transformer is ideally suited for outdoor exposed locations such as Barrow Island, WA.
