Energiforsk 2018-540 Framtidens Nätstation (2018)

Full citation: Sjöberg, G., Wämundson, M. & Karlsson, D. (DNV GL). Framtidens nätstation. Energiforsk Report 2018:540. Stockholm: Energiforsk AB, December 2018. Program: Smarta Elnät. ISBN 978-91-7673-540-4.

Open access: Published by Energiforsk. Project reference group included Vattenfall, Ellevio, Svenska kraftnät, Kraftringen, Öresundskraft, and Karlstad El & Stadsnät; programme board chaired by Vattenfall Eldistribution.

Summary

A DNV GL study for Energiforsk’s Smarta Elnät programme on how Swedish secondary substations (nätstationer — the 12–24/0.4 kV transformer stations between the fördelningsstation and the customer) should evolve. The report’s central finding is a plainly stated information gap, illustrated with a concrete Vattenfall field trial, and it proposes a four-tier maturity model — bronze, silver, gold, platinum — for how much a given nätstation can measure, control, and reason about itself.

Key claims

The core problem — informationsbrist

“Det övervägande problemet, som delas av flertalet elnätsföretag, är att man helt saknar information om förhållandena mellan utgående fack i fördelningsstationen (mellanspänningsnivå) och kundanslutningspunkter (dels på mellanspänningsnivå, dels på lågspänning).”

The report states this as the dominant, shared problem across most Swedish DSOs — not lack of primary equipment (transformers, cables), but lack of information about how the network between the distribution-station’s outgoing bays and each customer connection point is actually configured and behaving. Consequences named directly: DSOs cannot monitor or attribute network losses, cannot reconcile actual power/energy flows against the documented network topology (kopplingsbild), become dependent on customers and the public to detect and report faults, and risk consequential damage from problems that better information gathering would have caught earlier.

Vattenfall field trial (14 nätstationer)

A concrete illustration cited from the reference group: Vattenfall installed energy metering in 14 of its nätstationer as a trial.

• 8 of 14 behaved as expected — measured losses matched documented topology.
• 1 of 14 showed negative losses — meaning the documented topology does not match reality.
• 5 of 14 showed inexplicably high losses — indicating component faults, incorrect customer metering, incorrect documented topology, or some combination.

In 6 of the 14 trial stations (the negative-loss and high-loss cases) actual measurement pointed to a fault or a data-integrity problem, such as a documented topology that does not match the network, once compared against the assumed network model.

Why measurement in nätstationer is hard

Suitable current/voltage measurement transformers are not universally available at existing nätstationer; retrofitting is especially difficult in older station types. Continuous current/voltage measurement would resolve much of the informationsbrist, including detecting nollfel (poor neutral contact or neutral-conductor breaks).

Asset age context

Cited from IVA’s Sveriges framtida elnät (2016): approximately 70% of Swedish local- and regional-grid components are older than 20 years, and approximately 37% are older than 38 years. The grid was not built out evenly — a large expansion 40–50 years ago means the network is now in an “extreme investment trough” (investeringspuckel), and retrofit conditions vary enormously station to station as a result.

The bronze/silver/gold/platinum maturity model

The report’s own framework for nätstation capability, in ascending order:

The step from bronze to silver specifically requires solving collection and communication of the desired information (e.g. metering values, station status) — the report frames this as the open question, not a solved problem.

Conclusion

Development potential is judged to lie mainly in metering and communication systems, not in primary apparatus (transformers, cables) — even a modest move to stations with simple communication and rudimentary metering would improve outage handling efficiency. Regardless of technical readiness, regulation (delivery-quality requirements) is judged the most significant driver of which upgrades DSOs actually pursue, since the revenue-cap framework is explicitly designed to make DSOs evaluate cost-effectiveness of measures against quality requirements.

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