For a 75/95 MVA transformer rated 220/110-70/15 kV, the typical vacuum level during insulation drying is usually in the sub-millibar range, around 0.2-0.5 mbar, and in many procedures it is kept below 1 mbar depending on temperature and moisture condition. During oil processing and degassing, vacuum oil purification units normally operate at a slightly higher level, commonly around 1-3 mbar, which is sufficient to efficiently remove dissolved gases and moisture from transformer oil.

A power transformer transfers bulk apparent power between grid voltage levels and is designed for high MVA capacity, thermal performance, and short-circuit withstand. A voltage transformer (instrument transformer, VT/PT) is a metering/protection device that reproduces primary voltage at a reduced, accurate level for relays and meters. Power transformers focus on efficiency, impedance, cooling, and insulation coordination; VTs focus on accuracy, phase error, burden rating, and dielectric strength.

HV is required for efficient transmission; LV is required for end-use safety. Transformers bridge voltage levels from generation to consumption.

Typical buyers include transmission and distribution utilities, IPPs, generation companies, industrial plants (steel, mining, petrochemicals, cement), railways, metro systems, data centers, large commercial campuses, EPC contractors, and sometimes large commercial buildings. They purchase transformers for new substations, plant expansions, grid upgrades, renewable interconnections, and replacement of aging fleet assets, usually via tendering or negotiated framework agreements.

Power transformers handle high voltage and operate near full load between generation and transmission; distribution transformers operate at lower voltage, lower utilization and deliver energy to end users.

It provides voltage transformation, isolation, and coordination between medium-voltage feeders and low-voltage service circuits.

It covers handling, lifting, oil filling, grounding, tap setting, testing, commissioning, and safety instructions for field installation.

IEC 60076-3 specifies dielectric testing requirements, including applied voltage, induced voltage, lightning impulse, and switching impulse tests. These tests verify insulation strength, withstand capability, and partial discharge limits for transformers intended for transmission and distribution systems.

40 ppm at 65 °C is not critical for moisture, because at this temperature the oil saturation level is high and relative saturation is likely low. The more serious concern is tan delta > 1, which usually indicates oxidized or contaminated oil, high acidity, or conductive aging products. DP = 520 means the paper is aged but still serviceable, so slowing further aging is important. An online dryer can help stabilize moisture and protect the paper, but it will not correct a high tan delta. First, check TAN, IFT, resistivity, and DGA. If oil quality is poor, oil reclamation or replacement is needed before relying on online drying.

Areva transformers (heritage now in GE Grid) were widely deployed in transmission and sub-transmission infrastructure, HV substations, nuclear plants, and industrial complexes that require long-life transformer fleets.