Not every investment can be supplied directly from the low-voltage (LV) network. When power demand exceeds the capacity of the existing LV infrastructure, building a dedicated medium-voltage to low-voltage (MV/LV) transformer station becomes necessary. When exactly is this required, and what does such an investment involve?
When Is a Transformer Station Needed?
A dedicated transformer station is required in the following situations:
- connection capacity above 40 kW — the practical limit for LV network supply,
- industrial and manufacturing facilities — factories, production halls, process lines with high-power motors,
- shopping centres and office buildings — due to the large number of loads and continuity-of-supply requirements,
- photovoltaic farms above 50 kWp — requiring connection to the 15 kV or 20 kV MV network,
- residential estates — the developer builds the station as part of the infrastructure.
Types of Transformer Stations
Three main types are used:
- Indoor (brick-built) stations — a masonry or concrete building with the transformer inside, common in urban areas and housing estates,
- Pole-mounted (overhead) stations — transformer on a reinforced concrete or lattice pole, popular in rural areas, capacity up to 250 kVA,
- Container (prefabricated) stations — ready-made concrete or metal modules, fast installation, capacity from 160 kVA to 2500 kVA.
Costs and Financing
Approximate costs for building a transformer station:
- pole-mounted station 100–250 kVA: PLN 80,000–150,000,
- container station 400–630 kVA: PLN 200,000–400,000,
- indoor station 630–1000 kVA: PLN 350,000–600,000.
Additional costs include the MV cable line from the nearest network point and the connection fee payable to the DSO.
Permits and Procedures
Building a transformer station requires:
- obtaining MV connection conditions from the DSO,
- a construction design prepared by a licensed designer with electrical qualifications,
- a building permit or notification (depending on the station type),
- coordination of the MV switchgear and protection settings with the DSO,
- acceptance tests and measurement protocols.
Maintenance Obligations
The owner of a transformer station is obliged to:
- carry out periodic inspections every 5 years (earth resistance measurements, thermographic surveys, transformer oil testing),
- ensure supervision by qualified electrical personnel with appropriate licences,
- maintain an operational logbook for the station,
- provide the DSO with access to the station in case of grid faults.
A properly designed and maintained transformer station operates reliably for 30–40 years.