Nirav Dhanani A step-up transformer raises the low-voltage AC output of solar inverters to a higher voltage for export, for example from 800 V to 33 kV or from 33 kV to 132 kV at the grid substation. Transformers are designed and tested to IEC 60076, and their losses and impedance feed the plant's energy and fault studies.
Key Takeaways
- Step-up transformer raises inverter LV to MV.
- Typical: 0.69/33 kV or 0.8/13.8 kV.
- Critical for utility-scale plant collection grid.
- Specified per IEC 60076 / IS 2026.
- One per central inverter; or one per group of string inverters.
Where the Step-up Transformer Sits in the Plant
On a utility-scale ground-mount plant, each central inverter converts DC from the array into three-phase AC at a relatively low voltage, commonly 690 V or 800 V, because that’s the practical output level for inverter power electronics.
Carrying that current any real distance at LV would mean thick, expensive cabling and significant I²R losses, so the plant’s step-up transformer sits immediately downstream of the inverter’s AC disconnect, often on the same skid, and raises the voltage to the 10-35 kV level used for internal collection feeders.
From there, multiple transformer outputs are gathered on the plant’s medium-voltage ring and routed to the site substation, where a separate main power transformer steps up again for grid evacuation.
This chain of voltage levels, inverter LV, step-up transformer MV, substation HV, is exactly what a plant’s three-line diagram is drawn to document, and it’s the section of the drawing set reviewers and utilities such as PGCIL scrutinize most closely during interconnection approval.
Sizing, Ratios, and Standards
Voltage ratio is set by matching the inverter’s AC output to the plant’s chosen collection-grid standard, 0.69/33 kV and 0.8/13.8 kV are the two ratios most commonly specified in Indian and international utility-scale designs.
Transformer kVA rating is sized to the inverter’s continuous AC output plus a margin for ambient derating, and units are typically specified per IEC 60076 (or the equivalent IS 2026 in India) covering insulation class, temperature rise, and factory acceptance testing.
On plants built around central inverters, it’s standard to dedicate one step-up transformer per inverter; plants using distributed string inverters more often group several units onto a shared transformer and switchgear station to keep the electrical balance-of-plant simpler to design and maintain.
Related Reading
Step-up transformer sizing rarely gets decided in isolation, it’s one line item in the broader electrical and civil scope of a utility-scale plant. Our guide to open access solar in India covers how plants using this same LV-to-MV-to-grid chain structure their power evacuation and commercial arrangements, and the PVsyst tracker yield study methodology walkthrough shows how the same MW-scale layouts that drive transformer sizing get modeled for yield before construction.
For teams benchmarking an operating ground-mount build against this same inverter-to-transformer-to-substation architecture, Heaven Green Energy’s ground-mount solar park EPC work is a useful reference point.
Disclosure: Heaven Green Energy is a Heaven Designs group company.
Frequently Asked Questions
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