Special Transformers
Dry-type and oil-immersed transformers for furnace, rectifier, traction, test-bay and isolation duty, where a distribution transformer would not survive the load profile.
- Rated power
- 25 – 25 000 kVA
- Primary voltage
- up to 35 kV
- Vector group
- Dyn11, Yyn0, Dd0, special
- Insulation
- Class B / F / H
- Cooling
- AN / AF / ONAN / ONAF
- Duty
- Furnace, rectifier, traction, test
A furnace transformer sees a short-circuit every time the electrodes strike. A rectifier transformer feeds a load that is not sinusoidal. A test transformer has to be stable at 5 % of its rating. None of these are distribution duty.
Electromash designs to the duty cycle supplied by the customer, including harmonic spectrum, K-factor and the expected number of through-faults over the life of the unit.
Both dry cast-resin and oil-immersed constructions are available, with off-circuit and on-load tap changers.
Key characteristics
Designed to the actual load spectrum
Harmonic content and duty cycle are design inputs, not a derating factor applied afterwards.
Through-fault withstand verified
Winding bracing dimensioned for the declared number and magnitude of short-circuit events.
Multi-secondary configurations
Phase-shifted secondaries for 12- and 24-pulse rectifier arrangements.
Replacement to existing footprint
Tank, bushing positions and rail centres can be matched to the transformer being replaced.
Construction
- Cast-resin or oil-immersed core-form construction
- Copper foil or disc windings depending on current and impulse level
- Electrostatic shield between windings on isolation duty
- Buchholz, oil level, winding and oil temperature protection
- Off-circuit tap changer ±2 × 2.5 % as standard
Available configurations
- Furnace, rectifier, traction, isolation, earthing, test duty
- Dry cast-resin (AN / AF) or oil-immersed (ONAN / ONAF)
- Off-circuit or on-load tap changer
- 12- or 24-pulse multi-secondary
- Seismic and marine qualification on request
Monitoring options
- Winding temperature via Pt100 and thermal image relay
- Oil temperature and level
- Buchholz gas and surge protection
- Fan and pump control contacts
2 series, 6 models
A series shares one design; the variants below differ by frame size and rating. This table is generated from the series definition — the variant list is never maintained by hand.
TF — furnace transformer series
Oil-immersed furnace transformers with on-load tap changer, braced for repeated electrode short circuits.
TR — rectifier & isolation series
Dry cast-resin transformers for rectifier, isolation and traction duty, including 12- and 24-pulse arrangements.
Principal applications
Suitable industries
Documentation for this family
PDFs supplement the pages above. Nothing here is required to establish whether a machine is a candidate.
- Download (mock)CatalogueSpecial Transformers — Technical CataloguePDF · 7.8 MB · Rev. 02 · updated 2025-12 · EN
- Download (mock)Data sheetTF Furnace Transformer — Data SheetPDF · 1.1 MB · Rev. 01 · updated 2025-12 · EN
- Download (mock)QuestionnaireTechnical Questionnaire — Special TransformersPDF / online form · 0.3 MB · Rev. 01 · updated 2026-06 · EN
- Download (mock)Data sheetTR Rectifier & Isolation — Data SheetPDF · 1.0 MB · Rev. 02 · updated 2026-01 · EN
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