500 kVA, 33/0.4 kV 50Hz Dyn11 ONAN Al Oil Immersed Transformer

The transformer is rated 500 kVA with a primary (HV) voltage of 33 kV, secondary (LV) voltage of 0.4 kV, and designed for 50 Hz operation.

Dyn11 is the vector group: D = delta connection on one side, y = star (wye) with neutral on the other, n = neutral available, and 11 indicates a 30° phase displacement between primary and secondary. This affects system grounding, parallel operation and protection coordination, so confirm compatibility with your network design.

ONAN stands for Oil Natural Air Natural: heat is dissipated by natural convection of insulating oil inside the tank and natural air flow over the tank/radiators. It is suitable for continuous loads under normal ambient conditions without forced cooling equipment.

It indicates an oil-immersed transformer built using aluminum conductors/windings or aluminum components and insulated with transformer oil. Specifics (e.g., conductor material, oil type: mineral or biodegradable) should be confirmed with the manufacturer or datasheet.

Common accessories include conservator tank with breather, oil level gauge, Buchholz relay, pressure relief valve, temperature gauges/thermostats, HV/LV bushings, surge arresters, and earthing provisions. On-request options may include on-load tap changers (OLTC), forced cooling (ONAF/ONAF+), and remote monitoring.

Parallel operation is possible if transformers have the same vector group, similar percent impedance, phase shift, and compatible ratings. For Dyn11 units, ensure identical vector group and follow manufacturer guidance on impedance matching and protection coordination.

Typical factory tests include winding resistance, voltage ratio, no-load (excitation) test, short-circuit impedance and load loss test, insulation (power-frequency) test, and visual/functional checks. Type tests (impulse, temperature rise, noise) are available per standards on request.

Regular maintenance includes periodic visual inspections, oil level and breather checks, sampling and testing of insulating oil (DGA, moisture, acidity), monitoring temperature and cooling surfaces, checking for leaks and tightening connections. Follow the manufacturer’s maintenance schedule for frequency and specific procedures.

Performance can be affected by high ambient temperatures and high altitude. ONAN cooling assumes moderate ambient conditions; derating may be required above specified ambient/altitude limits. Obtain manufacturer derating curves for precise guidance.

Install on a suitable foundation, use specified lifting points, provide solid earthing/grounding for tank and neutral, install surge protection, and follow lock-out/tag-out procedures during commissioning. All work should be performed by qualified personnel per local electrical codes and standards.

Service life of a well-maintained oil-immersed power transformer is commonly several decades (20–40+ years), depending on loading, environment and maintenance. Warranty terms (duration and coverage) vary by manufacturer and should be confirmed at purchase.

Perform post-installation checks: insulation resistance, ratio and polarity test, winding resistance, continuity, proper grounding, oil level and breather condition, bushing integrity, and functional checks of protective devices. Carry out a controlled energization and monitor temperatures and oil behavior.

Oil-immersed ONAN transformers can tolerate short-term overloads within manufacturer-specified limits (temperature rise and thermal capability). Exact overload capacity and permissible durations must be obtained from the manufacturer’s thermal/overload curves.

Detailed mechanical drawings, weights, center-of-gravity, lifting points and foundation bolt layouts are provided by the manufacturer or in the product datasheet. Request the mechanical package before planning transport and installation.