Brochure · EN — Siemens Energy application brochure (2025) on the micro substation: a pre-assembled, transportable solution that connects directly to an existing high-voltage transmission line and converts high voltage to low voltage in one step, bringing electricity to remote areas without grid reinforcements. Built around a station service voltage transformer (SSVT) covering 72.5 kV to 550 kV on the primary side and 100 V up to 900 V on the secondary side, it is offered as a single-phase solution (up to 333 kVA) or a three-phase solution (up to 1 MVA with three SSVTs, scalable), can be fully assembled SF6-free with the blue portfolio (vacuum switching and clean air insulation), and is suitable for low-temperature applications at -50 °C and below.
The micro substation delivers electricity accessibility through a tailor-made solution for applications such as electrifying remote areas by a direct connection from the existing transmission grid — one step from high voltage to low voltage.
The brochure covers four topics: benefits & flexibility, the single-phase solution, the three-phase solution, and the micro substation's SF6-free technology basis.
The brochure lists eight headline benefits: electricity accessibility; economical solution for remote areas; minimum civil works required; transportable solution; one-step from high voltage to low voltage; applicable solution with blue portfolio; pre-assembled concept; and quick installation on site.
On flexibility: single-phase and three-phase solutions are available as per power demand; solutions come with the latest technology (SF6 free); and substation arrangements are tailored to each location and customer's needs, utilizing options such as skids platform, steel structures or foundations.
The worked example shown is a 145 kV micro substation using AIS technology, with circuit breaker integrated and station service voltage transformer (SSVT) with 167 kVA. Its single-line diagram places the following elements on the HV skid plate (AIS section) and downstream, reproduced verbatim from the diagram labels in the table below.
| Diagram element (as labelled) | Position in the 145 kV example single-line diagram |
|---|---|
| -D51 (arrester symbol) | On the HV skid plate (AIS section), branching from the incoming high-voltage connection |
| DIS | Disconnector switch on the HV skid plate, in series below the incoming connection |
| PORTABLE EARTHING | Earthing point on the HV skid plate, between DIS and CB |
| CB | Circuit breaker on the HV skid plate, below the portable earthing point |
| CT | Current transformer on the HV skid plate, last element before leaving the skid |
| Cable/Jumper | Connection from the HV skid plate down to the transformer |
| PVT — 145/0.415 kV, 167 kVA | Voltage transformation stage (the SSVT of the example), fed via the cable/jumper |
| NCT | On the earthed neutral connection at the transformer stage |
| Cable | Low-voltage outgoing connection below the transformer |
Electricity accessibility is crucial: it enhances quality of life by providing access to lighting, communication, and refrigeration, and supports education, healthcare and economic development. According to the International Energy Agency (IEA), around 770 million people worldwide do not have access to electricity, many of them in remote areas. Development should also reduce reliance on traditional fuels, leading to improved environmental conditions.
Many high-voltage transmission lines already cross areas where the energy is needed, but the high voltage must be converted to low voltage before connecting the final application (e.g. homes, 5G antenna and auxiliary services). The micro substation converts the high voltage directly to low voltage, ready for use: through a station service voltage transformer (SSVT) in a range of 72.5 kV to 550 kV, the voltage is transformed directly to voltage ranges between 100 V up to 900 V.
To ensure operational safety, switching equipment such as circuit breakers and disconnector switches is used. A current transformer measures the current flowing in the micro substation, and surge arresters may also be installed to protect from high-voltage impulses. The single-phase solution can deliver power up to 333 kVA on the secondary side.
When larger power is needed, the three-phase solution supplies a higher value of power — for example in remote areas near highways with a high-voltage transmission line, where a three-phase micro substation can supply applications such as an EV charging station. With three station service voltage transformers (SSVT), up to 1 MVA can be supplied; the solution is designed to be easily scalable by aggregating additional SSVTs whenever demand requires it.
The micro substation is supplied with the protection system customized according to customers' standards. Its connection to an overhead line does not disturb the current performance of the energy transmission; if a fault occurs inside the micro substation, the protection system can discriminate the source of the fault since current transformers are installed on the high-voltage side.
The pictured deployment example is a 145 kV micro substation using AIS technology, with circuit breaker integrated and SSVTs supplying power of 500 kVA — a Siemens Energy solution for an e-charger licensed by a European transmission system operator (TSO).
The micro substation can be completely assembled with SF6-free solutions. Siemens Energy offers the blue portfolio, including vacuum switching technology and clean air insulation, to produce zero harmful emissions without compromising on performance or economic feasibility. With over 10 years of experience in high-voltage vacuum switching, outstanding levels of technical performance and low lifecycle costs have been maintained while reducing the ecological footprint and increasing long-term sustainability — making the blue portfolio the choice for substation applications. It provides the same electrical and insulation features as traditional insulation technologies while giving all the benefits of an SF6-free solution, and is suitable for low-temperature applications at -50 °C and below.
On quality of service, the brochure names "virtually unlimited" power availability and sustainability: the solution provides the quality of supply of a transmission grid to the final customer. The average interruption time of a transmission grid is usually significantly lower than that of a distribution grid, since distribution grids are more affected by external factors such as storms, high winds, heavy snow or forest fires.
The solution is focused on situations where: consumers do not have access to MV/LV energy; quick installations with minimum civil works are available on site; and overhead lines (OHL) are available for usage — mainly outside urban centers, where rural distribution grids can have difficulties supplying the power demand. Finally, the micro substation is a sustainable solution: it gives a new use to existing transmission grids already available across countries, without the need for grid reinforcements due to new power requirements.
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