Brochure · EN — Siemens Energy brochure (© 2024, publicly published) presenting the power transformer portfolio: machine (generator step-up) and network transformers from 30 to over 1,300 MVA, up to the 800 kV insulation class, built to IEC 60076 and ANSI/IEEE. It walks through the global 13-factory production network, the manufacturing chain (core, windings, tap changers, tank, cooling, final assembly), factory testing, lifecycle services, a total-cost-of-ownership methodology with an illustrative loss-optimization example, and four project references including the first 400 MVA/420 kV natural-ester transformer and the first 400 kV ester-filled MIDEL 7131 unit.
Every power transformer is a one-off design, engineered around the customer's voltage, power rating, climate, network topography, noise limits, and many other criteria. Siemens Energy translates these individual requirements into transformers with a reputation for reliable operation over many years.
All Siemens Energy transformer plants worldwide operate consistently certified quality-management systems such as DIN ISO 9001:2008, backed by more than a century of experience in the field and continual research and development.
For more than 100 years the company has partnered with power supply and industrial companies around the world, supporting the full journey from planning, design, and production through transport, commissioning, and after-sales service. Transformer Lifecycle Management extends the service life of installed units and accommodates special customer requirements.
The chief applications are machine and network transformers. Equipped with on-load or deenergized tap changers — or a combination of both — they hold a constant output voltage.
Units are manufactured to the intended application and customer requirements as single-phase or three-phase designs, as multi-winding transformers or autotransformers, with power ratings up to 1,300 MVA and voltages up to the highest insulation class of 800 kV. They can also be designed to be fully or partially transportable.
All transformers are built to IEC 60076 and other international and national standards such as ANSI/IEEE and IEC. Recent innovations that have entered the standard delivery range include extra-quiet transformers, eco-friendly liquid dielectrics, and DC compensation solutions.
Siemens Energy manufactures power transformers in 13 factories on four continents: Nuremberg, Weiz, Zagreb, Linz, Trento, Dresden, Jundiaí, Tenjo, Guanajuato, Guangzhou, Wuhan, Jinan, and Charlotte (under construction at time of publication).
Harmonized design, globally standardized design guidelines, and common IT programs across all plants ensure customers receive the same product quality regardless of which factory builds the unit, while a modular principle accommodates customer-specific requirements.
The network's stated advantages: prompt bid preparation, optimized end-to-end project management, noticeably shorter production and delivery times, very high delivery reliability, flexibility through backup factories, fast standardized documentation, and just-in-time delivery.
The iron core is built from high-grade, cold-rolled, laser-treated sheets with thicknesses of 0.3 mm or less, precision-cut on computer-controlled machines. Sheets are stacked manually using the step-lap technique, giving especially good flux distribution at the joints and therefore exceptionally low losses and minimal no-load noise. A hydraulic platform then raises the finished core into the vertical position for winding assembly.
Windings face continuously high electrical and mechanical loads. Disk and cylindrical coils with transposed copper conductors provide high mechanical strength and long operational reliability. High-voltage disk coils are continuously wound — minimizing soldering points — and divided by radial and axial channels for oil cooling; precise control systems maintain contact pressure and winding tension throughout. Low-voltage multi-layer windings consist of concentrically superimposed cylindrical coils separated by axial oil ducts.
After winding, the coils are pressed, dried under constant pressure, impregnated with oil, measured exactly, and geometrically adjusted where required.
Grid and generator voltage can deviate significantly from the rated value, so every transformer provides a means of adapting its voltage to grid conditions: either in the deenergized state via a deenergized tap changer, or in steps under load via on-load tap changers.
On-load tap changers — and optionally deenergized tap changers — are fitted with a motorized drive and can be controlled locally or remotely.
The tank houses the core-and-winding assembly and the insulating oil, which together often weigh several hundred tons. It must add little extra weight yet remain structurally sound and leak-proof under mechanical stress; first-class corrosion protection is a basic requirement for long tank life.
Cooling is dimensioned to avoid hot spots and excess heating. The principal systems are ONAN, ONAF, OFAF, and ODAF oil-air cooling and OFWF and ODWF oil-water cooling; radiator banks and oil-air or oil-water coolers can be mounted on the transformer or installed separately.
In final assembly, axial shear forces are minimized by a joint press ring for all windings on a core limb, fixing the geometrical position of the individual windings. The core-and-coil assembly is dried in a vapor-phase system under vacuum at 130°C; while still above 100°C, all bolted connections are tested and secured and the assembly is tanked as quickly as possible, then immediately filled with insulating oil so the insulation absorbs no ambient moisture. After attachments such as the motor drive, control cabinets, bushings, and monitoring equipment are fitted, the transformer rests unenergized before final testing.
Every factory has its own high-voltage test bay. The test program spans voltage tests — including lightning impulse voltage withstand — temperature-rise tests, and special tests for insulation resistance, harmonics, and noise level. Short-circuit tests are performed at internationally recognized and approved institutes. A transformer is dispatched only after final inspection and testing succeed.
After delivery, Siemens Energy handles transport and, on request, installation and commissioning. Lifecycle services cover oil analysis and fault diagnosis, online monitoring, maintenance and repair, fast procurement of spares, and retrofits; the Transformer Academy provides customer training on every aspect of the units.
Because transformers repay their cost over decades, the purchase price alone should not drive the buying decision — operating costs, downtimes, and failure risk belong in the equation. Efficiencies of over 99 percent are standard, and more efficient transformers are also quieter; where extra-quiet operation is needed, "whisper transformers" actively remedy the root cause of transformer hum rather than relying on passive attenuation.
Alternative liquid dielectrics — mineral-oil alternatives, silicone oils, and synthetic and natural esters — enable deployment in locations with particularly high safety requirements such as nature reserves, groundwater protection areas, or offshore.
Reliability engineering targets maximum short-circuit strength, overload capability, high-temperature operation, reliable start-up after a power outage, and low maintenance costs, since unscheduled disconnection from the grid causes high costs.
The brochure compares two illustrative transformer designs to show the method: evaluation depends on purchase price plus total operating costs (TOC = Cc + CP0 + CPK + CD). In the printed example, the energy saving of the loss-optimized transformer of $168,996 per year pays for the increased purchase price of $276,361 in less than 2 years. Example A (low-cost design): no-load losses 200.01 kW, load losses 904.70 kW, purchase price $2,679,337, total cost of owning and operating $2,425,211 per year. Example B (loss-optimized design; printed as "Low-optimized"): no-load losses 217.49 kW, load losses 763.3 kW, purchase price $9,995,698, total cost of owning and operating $2,256,215 per year. (Values are the brochure's illustrative example, reproduced as printed.)
| Parameter | Symbol | Formula | Value | Unit |
|---|---|---|---|---|
| Depreciation period | n | - | 30 | years |
| Interest rate | p | - | 12 | % |
| Energy charge | Ce | - | 0.25 | $/kWh |
| Demand charge | Cd | - | 350 | $/kWh |
| Equivalent annual load factor | a | - | 0.8 | - |
| Depreciation factor | r | r = p*q^n/(q^n-1) | 12.41 | - |
| Interest factor | q | q = p/100+1 | 1.12 | - |
| Purchase price | Cp | $/ | ||
| Capital cost | Cc | Cc = Cp*r/100 | $/year | |
| Cost of no-load loss | CPO | CP0 = Ce*8760h/year*P0 | ||
| Cost of load loss (printed as "Cost of no-load loss", an evident misprint) | CPK | CPK = Ce*8760h/year*PK*α | ||
| Cost resulting from demand charge | CD | CD = Cd (P0+Pk) | 650 mm |
Kupferzell, TransnetBW, Germany (2019): first transformer with natural ester at a rating of 400 MVA/420 kV, with improved cold start thanks to a lower pour point at -30°C. Total weight 460 tons; insulation liquid Midel eN 1204 natural ester; cooling type KDAN/KNAN.
Consolidated Edison, New York, USA (2020): 100 MVA single-phase 60 Hz resilience transformer with plug-in bushings and cable connections, transported oil-filled, rated for full ConEd overload conditions (e.g., 169%, 1 hour, at 30°C ambient). LV with alternative plug-in cable connections to grid; OLTC and DETC for voltage regulation and switching between operating voltages; noise level 70 dB(A) no-load; KDAF cooling with MIDEL 7131 synthetic ester; hybrid insulation using NOMEX and TUP.
First Sensformer Advanced, Allgäu Überlandwerke, Germany (2021): 31.5/40 MVA, 112/20 kV power transformer with new virtual sensors from a thermal digital-twin model (virtual top-oil temperature and HV/LV winding hot-spot temperature) plus additional real sensors beyond the usual specification — ambient temperature sensors on both sides, LV winding current, and oil-temperature cooler inlet/outlet on both sides. Cooling ONAN/ONAF, KDAF with MIDEL 7131 synthetic ester, hybrid NOMEX/TUP insulation.
Highbury, National Grid UK (2015): first-ever 400 kV ester-filled MIDEL 7131 transformer — a 240 MVA three-phase autotransformer, 400/132/13 kV, with a heat-recovery system for school and residential buildings and an ultra-low-noise cooler at 30 dB(A) at 10 m. (Pictured as a 300 MVA three-phase autotransformer.)
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