HENTG POWER 400kVA 11kV/0.4kV 500KVA Three-Phase Oil-Immersed Transformer with ONAN Cooling for Commercial & Industrial Use

The HENTG POWER 400kVA oil-immersed transformer is designed for 11kV primary / 0.4kV secondary distribution in commercial complexes and industrial factory environments.
Rated at 50Hz, ONAN (Oil Natural Air Natural) cooling, this three-phase transformer meets IEC 60076 standards.
It is optimized for Nigeria’s grid conditions and tropical ambient temperatures (up to 45°C), providing reliable step-down power from 11kV medium voltage to 400V three-phase / 230V single-phase end-user supply.

• IEC 60076-compliant core & windings – Grain-oriented silicon steel (M5 grade, 0.23mm thickness) reduces no-load loss by consistent magnetic flux density (1.65T).

• Sealed tank design (corrugated wall) – Expansion corrugated fins absorb oil volume variation from -5°C to +55°C ambient, eliminating conservator-related leakage risks.

• High overload capacity – ONAN cooling allows 1.2x continuous overload for 6 hours within 45°C ambient without winding hotspot exceeding 105°C (class A insulation, 220°C cellulose paper).

• Dyn11 vector group – Handles unbalanced loads common in Nigerian commercial clusters (shops, factories with welding equipment).

• Low noise operation – ≤55 dB(A) at 1m distance, measured per IEC 60076-10.

• Anti-condensation treatment – HV/LV bushing sealing with NBR rubber (shore A 70±5) and hydrophobic coating on terminals for high-humidity coastal regions (Lagos, Port Harcourt).

• Rated power: 400kVA

• Primary voltage: 11kV ±2×2.5%

• Secondary voltage: 0.4kV

• Frequency: 50Hz

• Vector group: Dyn11

• Impedance voltage: 4.5% (±5%)

• Core: Step-lap stacked, cold-rolled grain-oriented silicon steel (M5, 0.23mm).

• LV winding: Copper foil (99.9% purity) – better short-circuit withstand than aluminum.

• HV winding: Copper wire (F class insulation, 155°C rated).

• Insulation paper: Thermally upgraded kraft paper (220°C melting point, permittivity 3.5).

• Tank: 3mm steel plate, hot-dip galvanized (Zn coating ≥ 85μm) for corrosion resistance in Nigeria’s humid/saline environment.

• Altitude: ≤ 1000m (customizable for Jos Plateau via derating)

• Ambient temperature: -5°C to +45°C

• Humidity: ≤ 95% non-condensing

• Corrugated tank with no rubber gasket on main body (only on manhole and bushings).

• Gaskets: HNBR (Hydrogenated Nitrile) for oil resistance, compression set ≤ 20% after 1000h at 120°C.

• Bushing sealing torque: factory set at 25Nm ±2Nm, with dual O-ring grooves.

• Paint system: Epoxy primer (80μm) + polyurethane topcoat (80μm) – passed salt spray test 720h (ASTM B117) with no creepage.

• Frequent grid surges and voltage fluctuations cause internal arcing and gasket aging.

• High ambient temperature (up to 45°C) + tropical humidity accelerate rubber seal degradation.

• Poor road conditions during transport lead to tank weld stress cracks.

• Local maintenance culture often lacks torque wrenches, leading to over/under-tightened bushing nuts.

In internal accelerated aging tests (85°C oil temperature, 90% RH, 500h cycle), the corrugated tank and HNBR gaskets showed zero visible leakage; torque retention remained within 22-28Nm range.

Q1: Can this transformer handle 33kV primary? We sometimes have 33kV feeders in industrial zones.
A: The standard model is 11kV primary. For 33kV applications, we offer a variant with 33kV bushings and reinforced insulation (36kV rated, BIL 170kV). Please specify voltage at order.

Q2: How do you prevent oil leakage during transport on bad roads from Lagos to Kano?
A: All HENTG POWER transformers are shipped with zero oil (dry). We use nitrogen-filled tank pressure (0.2 bar) to detect weld leaks before shipment. After installation, first oil fill is done on-site – this eliminates transit vibration leakage.

Q3: What is the standard warranty and do you have a local agent in Nigeria?
A: 24-month warranty from commissioning date or 30 months from shipment, whichever earlier. We have a technical partner in Lagos with stock of bushings, gaskets, and DGA test kits. Service response within 48 hours.

Q4: Can we use this transformer for a cold storage facility with frequent on/off cycling?
A: Yes – the Dyn11 vector group and copper winding (low thermal expansion mismatch) tolerate daily load cycles. However we recommend no more than 4 full load cycles per day to avoid cumulative insulation stress. For frequent switching (e.g., 10 cycles/day), we suggest optional load tap changer (OLTC) – consult HENTG POWER engineering.

Q5: What type of transformer oil is pre-filled? Can we use local oil?
A: Factory-filled with inhibited mineral oil (IEC 60296, grade A, breakdown voltage ≥ 60kV/2.5mm). Local oil can be used only if it meets same dielectric strength and pour point (-30°C) – we advise sending sample to our lab for compatibility test.

Q6: What grounding system do you recommend for Nigerian factories (TN-C or TT)?
A: The LV winding (0.4kV side) comes with a removable neutral link. For TN-C systems, we recommend solid neutral grounding. For TT, use the neutral link with surge arrester (MOV 275V) – not included but can be ordered as accessory.

HENTG POWER specializes in medium-voltage oil-immersed transformers (50kVA to 10MVA) for emerging markets, with a dedicated engineering team for tropical and high-salinity environments.

• IEC 60076-1 to -10 compliant design (Type-tested at KEMA or equivalent independent lab)

• ISO 9001:2015 production facility

• Short-circuit withstand test passed: 400kVA model at 11kV, 4.5% impedance, 25 cycles (IEC 60076-5)

• Core cutting: Silencer shear line with 0.02mm accuracy, step-lap joints.

• Vacuum drying & oil filling: Residual moisture ≤ 0.5% in insulation (measured by Karl Fischer).

• Pressure leak test: 0.3 bar air pressure for 12 hours – zero drop allowed.

• Partial discharge (PD) test: ≤ 10pC at 1.1× rated voltage (IEC 60076-3).

• Every transformer shipped with individual oil sample test report (breakdown voltage, moisture, dielectric dissipation factor).

• Customizable for 50Hz grid fluctuations (±10% voltage, ±5% frequency) – internal design margin for +15% voltage.

• 10-year spare parts availability commitment for gaskets, bushings, and cooling fins.