An evaluation of the environmental impact and of the safety of compact and modular equipment using SF6 up to 36 kV

In high voltage electrical installations (up to 36 kV), there has recently been a considerable increase in the use of compact and modular equipment whose insulation and cut-off medium is SF₆ gas. The reasons for this increase are: enhanced reliability; improved degree of safety; zero maintenance; and a huge reduction in volume. Pure SF₆ is an innocuous gas. It is assigned a threshold limit value (TLV) similar to that for any inoffensive gas not present in the usual working atmosphere, and its use can present new environmental conditions in transformer substations. This paper examines the most extreme environmental situations that can occur inside a transformer substation caused by accidental gas leaks, such as oxygen displacement, and the concentration of by-products for each situation, and their comparison with the TLVs required by the ACGIH (American Conference of Governmental Industrial Hygienists). Cases examined are: during the installation of equipment; during the equipment working life; due to internal arcing; and during the recovery of the equipment