NAEEA+
Every PV system is required to be protected by NS protection. This protection is already built into PV inverters. Nevertheless, the requirement has been for it to be additionally installed as an external protective device. Rightly so?
Factsheet
- Lead school School of Engineering and Computer Science
- Institute(s) Institute for Energy and Mobility Research IEM
- Research unit(s) IEM / Photovoltaic systems
- Funding organisation Schweizerische Eidgenossenschaft (Bundesverwaltung)
- Duration (planned) 01.12.2022 - 01.01.2025
- Project management Prof. Dr. Christof Bucher
- Head of project David Joss
- Project staff Theo Zwahlen
-
Partner
Bundesamt für Energie BFE
ETH Zürich (Leading House)
Fachhochschule Nordwestschweiz FHNW
Technische Universität Graz
SWISSOLAR - Schweizerischer Fachverband für Sonnenenergie
FGH Mannheim
Kühn - Netz und Systemschutz
Kreuter Electric GmbH
IWB
Groupe E SA
Primeo Energie
Repower AG
Romande Energie SA
SAK AG
Swissgrid AG
Technische Betriebe Weinfelden AG
VSE
VSEK
WWZ Energie AG
AET
AEW Energie AG
BKW Energie AG
CKW AG
EKZ - Energiecontracting
Eniwa AG
ewl - Energie Wasser Luzern
EWS AG
ewz - Keywords Grid connection of photovoltaic systems, NS protection, country settings Switzerland
Situation
The safety of the electrical grid can only be guaranteed if the grid voltage and grid frequency remain within prescribed, narrow limits. If these limits are exceeded, there is a risk of damage to electrical devices, but especially to large power plants. To prevent this from happening, they disconnect from the grid. The resulting power grid failure causes a blackout, at least locally. Photovoltaic systems (PV systems) also have to decouple from the grid, as it would be dangerous if an improper grid condition were prolonged by PV systems. It is for this reason that every PV system is required to have an appropriate protective function, which goes by the name of “NS protection”. Up until 2024, there was much debate as to whether this protective function could be integrated into the inverter or whether there should be an additional external configuration too. Since 2014, and even more explicitly since 2020, the NA/EEA Industry Recommendation of the Association of Swiss Electricity Companies (VSE) has called for PV systems of 30 kVA or over to be equipped with external NS protection. There was much discussion of reasons for and against external NS protection, but no consensus was ever reached. Ultimately, each grid operator makes its own decision as to what applies in its area of the grid. A large consortium consisting of various network operators, associations and universities from Switzerland, Austria and Germany got together in 2022 to find a joint solution to this issue.
Course of action
The following work packages were worked on under the direction of the Research Centre for Energy Networks (FEN) of ETH Zurich: Work package 0: steering committee Work package 1: Qualitative NS protection analysis (AP1.1: Needs assessment for protection behaviour and NS protection configurations (lead: VSE FG Schutztechnik & Swissolar); AP1.2: Basic NS protection function, relevant standards (lead: FHNW); AP1.3: Process analysis (lead: University of Graz); AP1.4: Experimental investigations (lead: BFH)) Work package 2: Quantitative NS protection analysis (lead: ETHZ) (AP2.1: Technical modelling and scenario definition; AP2.2: Selection of criteria and target values for safety quantification; AP2.3: Execution of the quantitative scenario analysis; AP2.4: Evaluation) AP3: Evaluation (AP3.1: Drafting of survey; AP3.2: Undertaking of survey, evaluation) The role of the PV Laboratory in the project is to investigate the behaviour of inverters with and without external NA protection in the event of grid failures. This involves searching for potential malfunctions and examining the switching transients on the grid and system side. The PV Laboratory also has a seat on the project’s steering committee.
Result
In June 2024, the project consortium came to the consensus that the disadvantages of external NS protection outweigh the advantages. The main disadvantages are: The fact that external NS protection offers no added value for any realistic and relevant failure scenario. The high cost of external NA protection. The high level of functionality and safety already built into the inverters. By adding additional complexity to the system, external NS protection renders it more susceptible to malfunction during commissioning and operation. The official communication from the project consortium can be viewed on the ARAMIS website (link below).
Looking ahead
The project members, who are also members of the relevant VSE expert committee that drafts the VSE’s NA/EEA Industry Recommendation, will incorporate the findings from the project into the new version, which is expected to be published in early 2025. But what applies in the meantime? This project has no influence on the legal situation: the distribution system operator stipulates whether or not external NS protection is required. Some grid operators are already doing without NS protection, while others continue to adhere strictly to the current VSE Industry Recommendation. Once the new Industry Recommendation is published, it can be assumed that external NS protection will no longer be installed.
