The latest European Commission proposal on Fluorinated Greenhouse Gases (F-gases) published earlier this year aims to reduce the use of Sulphur Hexafluoride (SF6), the extremely potent greenhouse gas (GHG), in medium voltage (MV) gas insulated switchgear (GIS) by two thirds by 2030 compared to 2014 [1]. Switchgear are key hardware components found throughout electrical infrastructure and act like grid-scale light switches - turning off and on different nodes of the grid.
However, currently, in EU regulation, there is no oversight of SF6 inventories, or emissions, in the MV segment, while oversight requirements in the high voltage (HV) segment are stringent. Considering that the amount of installed SF6 in the MV segment is equal to the amount installed in the HV segment, how is this the case? How could emissions containment and inventory reporting be used to reduce emissions, and encourage the adoption of sustainable switchgear alternatives? This article explores these, and other related, questions.
Why is it important to track and, where possible, limit the use of SF6?
SF6 is the world’s strongest greenhouse gas. It has a global warming potential (GWP) of 25,200, which means that 1 kg of SF6 is equivalent to 25,200 kg of CO2 [2]. Also, it has an extremely long atmospheric life-span of 3,200 years [3]. Thus, even a relatively small amount of SF6 represents a serious environmental problem.
Annual SF6 emissions are around 8,000 tons which is equivalent to the yearly CO2 emissions produced by around 100 million cars. To make matters worse, by 2030 its installed base is expected to grow by 75% (from 2019 levels) [2]. It is commonly used in high voltage (HV) and medium voltage (MV) electrical switchgear, transformers and substations as an electrical insulation, arc quenching, and cooling medium.
Furthermore, SF6 destruction is very difficult and expensive. A 2020 California Air Resource Board (CARB) report underlined that though “recycling of used SF6 is common practice, it is usually not destroyed because of the difficulty and cost associated with destruction. Therefore, it can be expected that SF6 that exists now and that is produced in the future will persist for thousands of years, whether in GIE equipment or, ultimately, in the atmosphere” [4]. For this reason, all installed SF6 should be considered banked emissions.
What is the difference between medium voltage (MV) and high voltage (HV) switchgear?
High-voltage switchgear
Standards for switchgear generally define voltages above 52 kV as high voltage (HV). This specification includes HV electricity distribution networks (e.g. 110 kV or 132 kV) and extra high voltage transmission networks (e.g. 220 or 400 kV). Other relevant networks covered here are, for example, connections in offshore wind farms (72 kV). A typical HV switchgear uses between 90 and 500 kg of SF6 [5].
Medium voltage switchgear
Switchgear between 1 kV and 52 kV is generally defined as medium voltage (MV). Within MV switchgear, we differentiate between primary and secondary distribution. A typical MV switchgear uses around 3.5 kg of SF6 [5].
Why is the use of SF6 in HV switchgear regulated differently compared to MV switchgear?
EU regulations on managing the use, and leakages, of SF6, apply only to GIS that contains 6 kg or more of the GHG [6]. As a result, rules with respect to HV GIS are stringent, while they are non-existent in MV GIS. This greater attention to the HV segment can be explained by the following [7]:
HV switchgear are responsible for a higher share of SF6 emissions during the operational phase
Per switchgear, they use a much larger amount of SF6
HV switchgear operate under higher gas pressure
SF6 leakage is more common because HV switchgear are not hermetically sealed
HV equipment are often older than MV equipment, and the older the equipment, the higher the risk of leakages.
For these reasons, strict regulations are applied to HV switchgear. These include [6]:
Product labeling
Leak prevention
Mandatory leak checks
Record keeping
Reporting of imports
Why do we need stricter oversight of SF6 in MV switchgear?
Despite the fact that individual HV switchgear uses more SF6 than MV switchgear, the SF6 operating inventory (banked emissions) in the MV segment is almost the same as in the HV segment (see fig. 1).
The reason for this is that grid infrastructure requires many more MV switchgear than HV switchgear. However, in the MV segment, regulation has no oversight of SF6 handling or associated emissions [8].
Fig. 1: Comparison of the SF6 inventory or SF6 operating emissions in Germany [8]
A study by the Fraunhofer Institute found the leakage rate from MV switchgear to range from 1.5% (industry best practice) to 40% (market worst case), with a best guess of 10% on average over the course of the MV switchgear’s lifecycle [9].
Similarly to the HV segment, in the MV segment, SF6 emissions occur through the following [10]:
Operation
There was a total decline in the SF6 operation emissions for the HV switchgear between 2010 - 2020 from 6 to 5 tonnes. However, for the MV switchgear operation, emissions increased from 1 to 1.5 tonnes during the same period [8].
Maintenance
During the service life of MV switchgears, up to 40 years, SF6 emissions that take place due to maintenance are estimated to be around 0.1% per year [11]. The reason for this, is that MV-GIS are generally designed to be maintenance-free.
Recycling
For MV switchgear, recycling is usually performed at the manufacturing plant. Although SF6 emissions occur during the recycling process, there is no reporting of the amounts emitted [12].
Destruction
In addition to being very difficult and expensive, SF6’s destruction process also results in a high level of emissions [4]. However, there is no reporting on the amount of SF6 emitted during its destruction process.
Why will this become increasingly relevant in the future?
Future projections indicate that network extension until 2050 will result in a 40% increase in MV switchgear installations [9]. This is mainly due to grid modernization, the increase in energy demand, and the further dissemination of renewable energy systems (see Fig 2 below). Since this increase in electrification by renewable energy is expected to occur at MV levels [8], switchgear that continues to use SF6 or other F-gases, should be more tightly controlled.
These increased operational requirements would help reduce emissions, provide incentives for the continued development - and adoption - of sustainable MV switchgear alternatives, which are increasingly becoming available.
Fig. 2: World energy consumption and electricity generation by energy type till 2050 [13][14]
Discussion
Exempting MV switchgear from SF6 reporting and inventory records is argued on the basis of practicality, mainly because the number of MV units is much greater than the HV units.
However, as the world fights climate change by moving towards an emissions-free electricity sector, business-as-usual is no longer an option. The MV GIS segment is home to 50% (and growing) of all banked, and recorded SF6 emissions. Therefore, it just can’t be the case that there is no oversight on how much SF6 is in circulation and being emitted over the course of a MV GIS’ lifecycle. For this reason, MV switchgear should be included in Articles 6 (Leakage detection systems) and 7 (record keeping) of the European Commission’s proposal on F-Gases [15].
In conclusion, tracking, and reporting the use and emissions of MV switchgear is crucial for mitigating the harmful impacts of the sector on the environment, and would further encourage the use of SF6-free alternatives.
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