Grid transformers and interconnecting autotransformers 380–400 kV
Grid transformers and autotransformers connect power systems of different voltages in the 380–400 kV class. A built example is an autotransformer of 250 MVA, 400/135 kV, vector group Yna0, KDAF cooling. They are used at 220–400 kV substations of the system operator and at renewable power evacuation nodes.
- Type
- transformers and autotransformers connecting systems of different voltages
- Example
- autotransformer 250 MVA, 400/135 kV, Yna0, KDAF cooling, vegetable ester
- Green autotransformer prototype
- 250/375 MVA, 400/135±10 % kV (2017), short-circuit withstand tested at CESI
- Insulating liquid
- mineral oil, natural or synthetic ester
Price, availability and lead time on request. We help with analogue selection, customs clearance and delivery.
Description
Transformers and autotransformers for power transmission connect power systems of different voltages and keep the trunk grids running without interruption. Growing demand for interconnections between national grids is one of the manufacturer's lines of work. These are nodes where a failure is felt by the whole power system. Such apparatus is designed individually, taking into account grid conditions and operator requirements. An interconnecting autotransformer has a common part of the winding between the 400 and 135 kV sides, so for the same throughput power it is lighter and smaller than a two-winding transformer. The manufacturer produces about 200 transformers a year to customers' needs, and grid apparatus is a separate line alongside shunt reactors and phase shifting transformers. For interconnection in the 380–400 kV class, rating, losses, noise and behaviour during short circuits are important, so they are built into the design in advance and verified during testing.
An example of a built project is an autotransformer of 250 MVA, 400/135 kV, vector group Yna0, KDAF cooling, with vegetable ester insulation, for the Martignone substation (Bologna). After the fire at the San Damaso substation, the unit was urgently relocated there to restore the grid. It was manufactured almost four months ahead of the contract deadline. Such speed is possible when design, manufacture and testing are brought together at one enterprise and the unit is designed for operation in a trunk grid.
The first large prototype of a green autotransformer of 250/375 MVA, 400/135±10 % kV was installed in 2017. It passed routine, type and special tests, including short-circuit withstand tests at the CESI laboratory (Rondissone), and has been in regular service since then. In 2026 the manufacturer received a contract for three autotransformers for the Danish grid.
The insulating liquid is mineral oil or natural or synthetic ester. Ester has a high flash point, so the substation footprint can be reduced, along with fire protection systems and oil containment requirements. Voltage regulation is by OLTC according to the project. Applications are 220–400 kV substations of the system operator, interconnections and renewable power evacuation nodes.
Technical specifications
| Type | transformers and autotransformers connecting systems of different voltages |
|---|---|
| Example | autotransformer 250 MVA, 400/135 kV, Yna0, KDAF cooling, vegetable ester |
| Green autotransformer prototype | 250/375 MVA, 400/135±10 % kV (2017), short-circuit withstand tested at CESI |
| Insulating liquid | mineral oil, natural or synthetic ester |
| Regulation | OLTC (per project) |
Replacement for
АТДЦТН-200000/330/110, АОДЦТН-167000/500/220, АОДЦТН-267000/500/220
selected by purpose and main parameters, please confirm with our manager
Request a price and lead time
Grid transformers and interconnecting autotransformers 380–400 kV. We reply within one business day.
Or email sales@usk.ua or call 044 339-50-20.
Questions and answers
What parameters does the built interconnecting autotransformer have?
It is an autotransformer of 250 MVA, 400/135 kV, vector group Yna0, KDAF cooling, with vegetable ester insulation.
Was the green autotransformer tested for short-circuit withstand?
Yes, the 250/375 MVA, 400/135±10 % kV prototype installed in 2017 passed short-circuit withstand tests at the CESI laboratory.
Which substations is this apparatus intended for?
For 220–400 kV substations of the system operator, interconnections and renewable power evacuation nodes. Ester insulation makes it possible to reduce fire protection systems.
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