What a Step-Up Transformer Does in Your Project
A step-up transformer raises the generator terminal voltage to the transmission or sub-transmission level so power can travel over distance with acceptable losses. In a power plant, a solar park, a wind farm, or a biomass unit, this unit sits between the generator bus and the switchyard. Because every megawatt has to pass through it, the step-up transformer is the single most consequential asset on the generator side and the one that decides how smoothly your plant connects to the grid.
A power transformer used as a generator step-up unit is specified differently from a distribution unit. It has to withstand continuous full load, tolerate harmonics from inverters, hold voltage under grid faults, and accept the thermal cycling of a plant that starts and stops. We build these units for continuous duty, not for the intermittent profile of a distribution network.
35-110kV 6.3-63 MVA IEC 60076
| Specification | Value |
|---|---|
| Rated capacity | 6.3 MVA to 63 MVA |
| Primary voltage (generator side) | 6.3kV, 10.5kV, 11kV, 13.8kV, 15.75kV, 21kV |
| Secondary voltage (grid side) | 33kV, 35kV, 66kV, 110kV, 132kV |
| Phase / frequency | Three-phase, 50Hz or 60Hz |
| Vector group | YNd11 (generator side delta winding blocks third harmonics) |
| Cooling | ONAN / ONAF / OFAF depending on rating |
| Insulation | Class A mineral oil, optional ester fluid for fire-sensitive sites |
| Tap changer | Off-circuit (NLTC) or on-load (OLTC) with remote control |
| Impedance | Typically 10-14 percent, tuned to your short-circuit study |
| Applicable standard | IEC 60076, IEEE C57 / ANSI C57 where required |
| Routine tests | Ratio, winding resistance, insulation resistance, no-load and load loss, induced and applied voltage, oil dielectric |
| Typical lead time | 30 days from approved drawings |
Matching the Unit to Your Generator and Grid Code
The first three decisions are the generator terminal voltage, the grid connection voltage, and whether an on-load tap changer is required by your grid operator. Those three answers fix the rating, the vector group, and the cooling class. For units feeding into a weak grid or a long radial line, we usually recommend OLTC so the plant can hold voltage without tripping during grid disturbances.
High-voltage units in the 66-132kV band are grouped under our high voltage transformer line. Typical examples include a 25 MVA 110/11kV unit, a 31.5 MVA 66/11kV unit, and a 63 MVA 110/11kV unit for large thermal and hydro blocks.
For renewable projects the inverter-side harmonic spectrum matters more than rating. We size the winding and core with a K-factor margin and, where the collector network is long, pair the unit with a compact substation so the step-up, protection, and metering arrive as one factory-assembled block.
Where These Units Are Installed
Technical Highlights
- Generator-side delta winding suppresses triplen harmonics before they reach the grid
- Impedance tuned to your short-circuit study rather than a catalogue default
- ONAF / OFAF cooling stages hold full output on hot days without derating
- OLTC option with motor drive and remote position indication
- Sealed conservator or fully sealed corrugated tank to keep moisture out
Application Scenarios
- Thermal, hydro, and biomass power plants feeding a sub-transmission network
- Solar PV plants connecting an inverter station to the 33kV or 66kV grid
- Wind farms with a generator-side collection network
- Grid substations needing a replacement step-up unit
- Captive and industrial generation with export to the utility
Key Features
- Core built from high-permeability grain-oriented silicon steel for low no-load loss
- Winding conductor sized for continuous full-load operation at 40 degrees ambient
- Terminal arrangements configurable to match existing busbar or cable boxes
- Full routine test report issued with every unit before dispatch
- Factory-witnessed or third-party witnessed acceptance testing
Optional Configurations
- Ester fluid or silicone fluid for fire-sensitive or indoor installations
- Marshalling box with RTD, Buchholz, and winding temperature wiring to terminal blocks
- Neutral grounding resistor mounting frame and CT provision
- Special painting or stainless fittings for coastal and high-corrosion sites
- Spare parts kit and oil filtration connection points
Testing Before Shipment
Every unit leaves only after its routine tests are complete and signed off. Fully assembled units also undergo a factory acceptance test sequence – see our FAT witness checklist for the exact list. For应试 the individual test methods and tolerances, our guide to IEC 60076 and IEEE C57 testing standards walks through each test.
Frequently Asked Questions
Can one unit step up from generator voltage directly to 110kV or 132kV?
Yes. Generator step-up units are regularly built with a low-voltage generator-side winding and a 110kV or 132kV grid-side winding in one tank. Where the plant already has a 33kV bus, a two-stage arrangement using a 33kV unit followed by a high-voltage unit is also common and sometimes cheaper to maintain.
Do I need an on-load tap changer?
Grid operators usually require OLTC when the plant must regulate voltage continuously or when the connection point voltage swings widely. If your grid operator allows voltage variation within a narrow band and you can accept off-circuit taps adjusted during outages, NLTC keeps cost and maintenance lower.
Which vector group is standard for generator step-up units?
YNd11 is the usual choice: the star-connected high-voltage winding gives a neutral for earthing, while the delta low-voltage winding provides a circulating path for third harmonics. Our vector group selection guide explains the trade-offs.
What information do you need to quote?
Generator terminal voltage and MVA, grid connection voltage, frequency, ambient and altitude conditions, cooling preference, and whether OLTC is required. With those six data points we can return a budgetary proposal quickly.
How long does delivery take?
Standard configurations ship within 30 days of drawing approval. Units requiring OLTC, ester fluid, or special enclosures take longer; we confirm the schedule with each quotation rather than quoting a single number for every case.