Medium-voltage switchgear insulated with SF6 (sulphur hexafluoride*) gas is less harmful to the environment than the associated cables, overhead lines and transformers, according to a joint study by leading power companies.
A life cycle assessment (LCA) study to acquire environmental data about medium voltage power distribution in Germany was recently commissioned as a joint project by ABB, Areva T&D (formerly ALSTOM), Siemens, EnBW, EON Hanse, RWE and Solvay Fluor.
The LCA study establishes an environmental profile comparing air-insulated and SF6-insulated switchgear. It shows that the total contribution of power distribution grids to global warming is very low. That switchgear technology in the medium-voltage range makes only a very minor contribution to the greenhouse effect. And, that ohmic losses (heat produced by electrical resistance) caused mostly by the use of cables, overhead lines and transformers are the principle ways a power grid contributes to the greenhouse effect.
This contribution can be even further reduced by the use of SF6- insulated switchgear systems, the study says. In addition, the ohmic losses of SF6-insulated switchgear are lower in the operational phase.
PROCEDURE AND SCOPE
The LCA was conducted in accordance with ISO 14040-43 standards and verified by TUV NORD CERT.
Data was gathered for a representative mix of medium voltage switchgear: transformer substations, ring main units and customer substations. It included key electrical figures (in particular ohmic losses), material data from disassembly analyses as well as electrical load and lifetime.
At grid level, two representative model grids were examined an urban and a rural region. At the switchgear level, a representative mix of medium voltage switchgear was determined based upon a current delivery statistic from the Zentralverband Elektrotechnikund Elektronik-industrie (ZVEI). It includes switchgear both for use in utility grids and for industry and infrastructure grids.
OHMIC LOSS FINDINGS
The LCA analysed representative power distribution networks in urban and rural areas, and found 92 percent of the contribution to the greenhouse effect made by power distribution comes from ohmic losses in cables, overhead lines and transformers, and only eight percent from switchgear. Switchgear of any type was found to cause only a relatively small proportion of these losses, and furthermore, the use of SF6 as an insulating and arc-quenching medium in switchgear is proven to be ecologically competitive compared to other forms of insulation.