Distribution transformers step down medium voltage (typically 10 to 30 kV) to the low-voltage level (400 V), supplying households, commercial premises, and smaller industrial facilities. They are by far the most commonly installed type of transformer in the power grid. As distribution grids shift toward bidirectional energy flows and smarter control, modern distribution transformers are taking on new functions.
What power ranges do distribution transformers have?
Distribution transformers typically range from 25 kVA to 2,500 kVA, and in special cases up to 10 MVA. They are predominantly oil-cooled and installed in substations – local substations, customer substations, or pole-mounted stations – but are also available in cast-resin variants for special requirements. The EU Ecodesign Directive requires particularly high efficiencies for new installations.
Key Characteristics at a Glance
- Ratings typically 25 kVA to 2,500 kVA
- Input medium voltage (10–30 kV), output 400 V
- Oil or cast-resin design depending on application
- Compliance with the EU Ecodesign Directive (Tier 2)
- Service life of 30 to 40 years or more
- Regulated distribution transformers with on-load tap changers
- Sensors for online monitoring increasingly standard
Frequently Asked Questions
How is a distribution transformer selected?
Decisive factors are the load forecast, the expected load profiles (day/night, summer/winter), the permissible losses, and the installation site. In the case of decentralized feed-in – for example from PV installations – reverse power flow requirements must also be taken into account.
How high are the losses of a modern distribution transformer?
A modern 630 kVA distribution transformer compliant with EU Ecodesign Tier 2 has typical no-load losses of around 0.6 kW and load losses of around 5.4 kW at full load – figures that were significantly higher just a few years ago.
What are regulated distribution transformers (rONT) and what are they used for?
They have an on-load tap changer that adjusts the secondary voltage during operation. This is particularly valuable in grids with high PV feed-in, since voltage fluctuations are automatically compensated for and more renewable generation can be integrated.
How is a distribution transformer correctly installed?
Important factors include a load-bearing foundation, adequate ventilation, correct earthing, standards-compliant clearances, and careful connection to the supply cables. For outdoor oil-type transformers, an oil containment basin is mandatory. Commissioning follows defined test protocols with documented measurements.
Do you need new or modernized distribution transformers? We supply standard designs and custom solutions – talk to our team.