800 kVA Oil-Immersed Transformer for Heavy Industrial Loads

Role of the 800 kVA Transformer in Heavy Industry

An 800 kVA oil-immersed transformer supplies medium-voltage distribution to large industrial loads such as manufacturing machinery, mining equipment, and continuous production lines. It steps down primary voltages of 10 kV, 20 kV, or 35 kV to utilization voltages of 0.4 kV or 1.14 kV, providing the power density required by factories and mine sites.

Design Features for Industrial Environments

Rugged Tank Construction

The tank is fabricated from 5 mm carbon steel with anti-corrosion and anti-impact coatings, providing better resistance to industrial dust, chemical fumes, and mechanical collision than a standard 3 mm tank.

High-Load Tolerance

Thickened copper windings with a conductor cross-section of at least 120 mm squared and a high-density silicon steel core allow the unit to carry 150% of rated load for one hour, which is important for batch production peaks.

Enhanced Cooling System

The ONAN cooling arrangement, Oil Natural and Air Natural, uses extended radiator fins to increase heat dissipation and maintain stable operation even in high-temperature workshops with ambient temperatures up to 50 degrees Celsius.

Industrial-Grade Protection

Pressure relief valves, oil moisture absorbers, and high-temperature alarms reduce failure risks during continuous industrial operation and protect the unit from overpressure caused by load spikes.

Performance Advantages

Low Energy Loss

The transformer is designed to meet the efficiency requirements of IEC 60076 and modern energy-efficiency classes for distribution transformers, with no-load loss as low as 850 W and load loss of about 6200 W. Low losses directly reduce electricity costs for plants that operate around the clock.

Stable Voltage for Sensitive Equipment

An off-circuit tap changer with a ±2x2.5% tapping range allows the secondary voltage to be adjusted for grid variations, protecting sensitive machinery such as CNC lathes and hydraulic systems from voltage fluctuation.

Long Continuous Operating Life

The sealed tank uses high-quality mineral insulating oil compliant with IEC 60296 with anti-oxidation additives, extending oil replacement cycles to 8-10 years. Core components have a design life of more than 30 years.

Low Maintenance Requirements

Oil level sight glasses and pressure gauges enable easy visual inspection. Only annual oil sampling and cleaning are required, minimizing maintenance downtime for industrial production.

Technical Specifications

Parameter	Specification
Rated Capacity	800 kVA
Primary Voltage	10 kV / 20 kV / 35 kV, customizable
Secondary Voltage	0.4 kV / 1.14 kV, three-phase four-wire
Frequency	50 Hz / 60 Hz
Cooling Method	ONAN
Insulation Class	Class A, mineral oil insulation
Temperature Rise	Top oil up to 60 K, winding up to 65 K
Protection Level	IP23 standard, IP54 optional for dusty or mining areas
Approximate Weight	4800 kg
Dimensions L x W x H	2800 mm x 1800 mm x 2200 mm
Short-Circuit Withstand	25 kA for 2 seconds
Applicable Standards	IEC 60076 series

Selection and Installation Notes

Choose the primary voltage to match the local grid, for example 35 kV for mining networks. For extreme high-load scenarios, an ONAF cooling upgrade with forced air can be specified. For dusty or chemically aggressive areas, an IP54 enclosure and corrosion-resistant coatings are recommended. Every unit should undergo routine and type tests according to IEC 60076 before delivery, including temperature rise, short-circuit withstand, and dielectric tests.

FAQ

Q1: What does ONAN cooling mean for an 800 kVA transformer?

ONAN stands for Oil Natural and Air Natural. The oil circulates naturally by convection and dissipates heat through the tank and radiator fins to the surrounding air, requiring no pumps or fans.

Q2: Can an 800 kVA oil-immersed transformer handle overloads?

Yes. The design can carry 150% of rated load for one hour, and smaller overloads for longer periods within the limits of IEC 60076-7, which supports batch production peaks in industrial plants.

Q3: How often should the insulating oil be replaced?

With high-quality mineral oil compliant with IEC 60296 and anti-oxidation additives, the oil replacement cycle is typically 8-10 years, provided annual oil testing shows acceptable quality.

Q4: What is the difference between IP23 and IP54 enclosures?

IP23 protects against solid objects larger than 12 mm and water spray up to 60 degrees from vertical. IP54 adds protection against dust and water splashes, making it suitable for dusty or mining environments.

Q5: Is a 35 kV primary version available?

Yes, the primary voltage can be customized to 10 kV, 20 kV, or 35 kV to match the local industrial grid, and the secondary voltage can be arranged as 0.4 kV or 1.14 kV.

Q6: What tests should be performed before commissioning?

Routine tests per IEC 60076 include winding resistance measurement, turns ratio test, dielectric tests, no-load loss and current measurement, load loss and impedance measurement, and temperature rise tests for type approval.