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Power Transformers

Two- and three-winding oil-immersed power transformers for substations, industry and renewable step-up, up to 31.5 MVA / 110 kV.

Porcelain high-voltage bushings on a power transformer

Power transformers

For primary substations, industrial plants and renewable-energy step-up, MARS manufactures oil-immersed power transformers from 3,150 kVA to 31,500 kVA at 35, 66 and 110 kV, with on-load or off-circuit tap changers, ONAN/ONAF cooling and two- or three-winding designs. Every unit is designed to IEC 60076 with the customer's impedance, vector group, tapping range and loss guarantees, and is available for witnessed FAT including temperature-rise and impulse tests.

Scope

  • Windings: copper, disc or helical HV, with electrostatic shields and transposed conductor where required.
  • Tap changers: on-load (±8 × 1.25 %) or off-circuit (±2 × 2.5 %).
  • Cooling: ONAN, ONAF, with detachable radiator banks and fan control; conservator with dehydrating breather.
  • Accessories: Buchholz relay, winding and oil temperature indicators, pressure relief, oil level gauge, current transformers, marshalling box.

Our FAT checklist explains the tests to witness; see a representative 66/11 kV grid configuration.

FAQ: Power Transformers

What impedance can you design?

Standard values follow IEC 60076-5 (for example 7–8 % at 10 MVA, 10–12 % at 31.5 MVA), but impedance is set with the buyer against fault level and voltage drop; higher or lower values are available within design limits.

Do you offer three-winding transformers?

Yes — 66/11/11 kV and similar three-winding units for dual-busbar distribution, and 110/35/10 kV units for regional substations, with independent tapping on the HV winding.

What documentation is provided?

Design review documents, outline and foundation drawings, nameplate, routine test reports for every unit, type-test reports, oil analysis, painting and packing specifications, and installation and maintenance manuals.

What lead time should I expect?

Typically 60–90 days for power transformers after drawing approval, depending on rating, tap changer and accessory lead times. Distribution transformers ship in 25–45 days.