Auto­
transformers

An autotransformer shares part of its winding between the primary and secondary circuits, while a two-winding transformer keeps them fully separate. That shared winding is why autotransformers run more efficiently and cost less at high MVA — but it also means they don't provide galvanic isolation between the HV and LV sides. For transmission interconnection, where both sides are already part of the same grounded network, that trade-off works in your favor. See our Power Transformers page for the fully isolated alternative.

Not typically. A GSU sits between a generator and the grid, and that interface usually calls for the full electrical isolation a two-winding design provides — it keeps a fault on one side from propagating directly to the other. LIMIK autotransformers are engineered for transmission-to-transmission interconnection, not generator interconnection. For generation applications, see our Generator Step-Up Transformers page.

It depends on your substation design. A tertiary winding is typically added when you need to supply station auxiliary loads at a third voltage, connect reactive compensation equipment (capacitor banks or reactors), or suppress harmonics from an otherwise wye-wye connected unit. If your interconnection doesn't call for any of those, a two-winding autotransformer without a tertiary is a simpler, lower-cost specification. Our engineering team can confirm which configuration your system needs.

Solid grounding is the standard configuration and keeps ground-fault currents at their natural magnitude, which most transmission protection schemes are built around. An NGR limits that fault current — used where a specific protection coordination study calls for a reduced ground-fault magnitude, or where equipment on the connected system has a lower fault-current withstand rating. This is a system-level decision made with your protection engineer, not a default choice.

No — LIMIK's autotransformer line is built for transmission voltage interconnection, not for controlling power flow direction between parallel paths, which is what a phase-shifting transformer does. If your project needs power-flow control rather than voltage-class bridging, that's a different unit type outside our current product line.

345/500 kV, 230/345 kV, 138/230 kV, and 115/230 kV cover most of the interconnections we're asked to engineer, but the unit is built to your actual system voltages, not a preset list. If your combination isn't listed, request a quote and our engineering team will confirm feasibility.

The same range applies across Power Transformers, Autotransformers, and Generator Step-Up units — all are engineered and built at the same class of manufacturing complexity. The clock starts once your specification is finalized. See the full comparison of LIMIK transformer types for how the three platforms line up side by side.