Ring main distribution switchgear-latest trends in use, control, and operation

For many decades the design of ring main units was based on the traditional oil filled concept with either oil immersed or air insulated HV fuse links in the tee-off circuit protecting the connected transformer. Whilst these units gave first class service over the years, there was recognition in the industry, during the late seventies, of a need for oil-free equipment to be developed in order to overcome fire hazard, environmental and maintenance considerations associated with oil. Here, the authors describe the latest trends in the use, control and operation of SF₆ ring main distribution switchgear