Development of 420 kV gas insulated switchgear with one–break spring operated gas circuit breaker

Reduction of life-cycle cost of high-voltage electric equipment including installation and maintenance costs is an increasing need for electric power utilities. In general, gas insulated switchgear (GIS), which is one of the high-voltage electric equipment, should be compact and have high-reliability that enables the reduction of installation period and maintenance work. 420 kV GIS with one-break spring operated gas circuit breaker (GCB) has been developed to meet the growing demand for substation construction together with the demand for reduced installation and maintenance costs. The paper presents key benefits and their supporting technologies applied to the developed GIS.

Reduced installation period is achieved by the compact design of GIS with concentrated configuration. Application of one-break GCB enables reduced size of GCB and contributes to the concentrated configuration of the primary circuit of the GIS connected to both sides of the GCB. Operating mechanism for GCB is arranged in front of GIS, which results in lower height of GCB and easy accessible for maintenance than that for existing GIS. Concentrated configuration enables single transportation per GIS unit and reduction of installation work to 60% because many gas compartments assembled in factory can be installed without assembly work on site. Compactness also reduces the installation footprint of switchgear to 60% of that for existing switchgear, and results in the reduction of building cost for the whole substation.

Reduced maintenance work is achieved by GCB with torsion-bar spring operating mechanism and flexible linkage applied to disconnectors (DS) and earthing switches (ES). Operating mechanism with torsion bar spring possesses enough capability to applied one break GCB while also providing benefits of increased mechanical reliability and reduced maintenance work. It also enables to design a compact operating mechanism with large stored energy, and higher interrupting capability can be achieved with simple mechanical puffer interrupter. Flexible linkage using metallic wires is applied to DS and ES to achieve easy access for maintenance work. Metallic wires transmit operating force from the operating mechanism to the moving parts of DS or ES, while enable the flexible location of the operating mechanism. They also contributes to concentrated configuration of all operating mechanisms located in front of the GIS unit, that results in enables single location for maintenance of the GIS unit and reduction of the maintenance work. Reduced environmental impact is achieved by the compact design of the developed GIS. SF₆ gas is reduced to 60% compared to existing GIS. Use of material can also be reduced to 50%. Type tests were carried out on prototype GIS in accordance with IEC standard.