In the afternoon of 17 July, the lights went out over large areas of Valais. Power failure. As a result of various construction projects in the transmission grid, protection tests were planned in the Chippis substation on that day. In the course of this work there was an unintended protective tripping of the grid node Creux de Chippis at 4.23 p.m. This led to the regional supply disruption in the distribution grid. Investigations carried out so far into this complex event have shown that a combination of technical and human factors led to the incident.
How did this incident occur?
Adrian Häsler: First of all, I would like to say that we are sorry for this incident. We sincerely regret any inconvenience caused by it.
The incident on 17 July is to be seen in the context of the grid expansion in Valais. The work is extremely complex and demanding. When checking the protection settings in the substation in Chippis, the busbar protection tripped out unintentionally. Investigations carried out so far have shown that a combination of technical and human factors led to the incident.
What were the technical factors?
There is grid congestion in Valais. The capacity of the transmission grid in the region in question is not adequate for transporting the energy from the high levels of electricity production of the alpine hydroelectric power plants in the summer. Incidentally, we recognised these grid congestion problems in the context of «Strategic Grid 2025» and addressed them in 2015. The grid expansion as planned by Swissgrid is essential to maintain the long-term security of supply. The «Chamoson – Chippis», «Chippis – Bickigen» and «Chippis – Lavorgo» projects will effectively eliminate the strained grid situation in Valais and hence increase the robustness of the whole of Swissgrid’s infrastructure in the region.
We recognized and addressed these grid congestion problems in the context of «Strategic Grid 2025».Adrian Häsler, Swissgrid
However until this work has been completed, Swissgrid will have to completely disconnect the transmission grid in the Mörel substation in the east-west direction for around 15 weeks of the year, in order to guarantee grid security and the necessary transfer capacity in the region. This will lead to lower fault tolerance in the region.
The ongoing grid expansion projects in Valais also resulted in adjustments to the operation of the Chippis substation, which affected the protection settings of the system. These settings were made by the contracted service provider in December 2019 and correspond to the usual procedure.
And which were the human factors?
Scheduled tests of protection parameters took place in the Creux de Chippis substation on 17 July 2020. Some errors were made in the process; for example, the system was not put into revision mode. In the course of the work the busbar protection was unintentionally tripped. Consequently the switchgear in the Chippis substation was disconnected from the power supply. As a result of the special grid situation, the substations in Stalden, Bitsch, Zermeiggern and Mörel were were also affected by the loss of power. This led to the regional supply disruption in the distribution grid.
The Swiss transmission grid is one of the safest in the world.Adrian Häsler, Swissgrid
Could this incident occur again anywhere?
It is extremely unlikely. The Swiss transmission grid is closely interconnected and is operated in accordance with the n-1 rule. If a grid element, such as a line, fails, no other element must be overloaded. As mentioned above, this level of redundancy was temporarily unavailable in the Chippis region. The supply disruption in Valais is an extremely rare occurrence. We are doing our utmost to deal with the incident thoroughly and conscientiously and to draw the correct conclusions, so that it is not repeated in future. We take this work very seriously and it is taking some time to complete.
Was it negligent to undertake this type of work in this configuration?
No. This type of work does not normally have any effect on the security of supply In addition to which, it was absolutely essential for the renovation of the connections between Bickigen, Chippis and Wimmis.
Has Swissgrid learned from this incident? And will these findings influence its day-to-day work?
We have already checked the processes for working on systems accordingly. The findings from the incident are being incorporated into the training of both internal and external specialists. It is important for me to emphasise that safety has top priority at Swissgrid. Safety for people, systems and the environment. We have a safety-first approach, which is firmly embedded in the company and at our service providers.
The safety of people, systems and the environment is top priority for Swissgrid.Adrian Häsler, Swissgrid
Are there many such incidents in the Swiss transmission grid?
No, the Swiss transmission grid is one of the safest and most stable in the world. According to the Swiss Federal Electricity Commission (ElCom), Switzerland scores top marks in terms of the quality of supply throughout Europe. The average outage duration per consumer and year in Switzerland was 19 minutes in 2019. Only 0.2 per cent of this can be attributed to the transmission grid.