GDF Suez Energy 275kV Gas-Insulated Switchgear

Following the completion of multiple repair and maintenance contracts at GDF Suez Energy Power Stations, TP Power Services were requested to quote for dismantling and re-sealing of the gas-insulated switchgear (GIS) connecting their 48MVA station transformer to the National Grid operated substation. With the sulphur hexafluoride diagnosed as leaking from the GIS’s transformer connection; each of the three phases had their gas removed for temporary storage, the section was stripped down to it’s component parts, gaskets inspected and replaced, re-greased and the system vacuum tested before refilling with the recycled gas and commissioned. In addition to the maintenance works on the GIS, the station transformer was given its 5 Yearly Maintenance and the conservator cell membrane were replaced.


Preliminary testing of the SF6 for oxygen, moisture and contaminated gases for integrity and safe handling
Removal of SF6 gas to half pressure in adjacent zones using DILO gas cart and flow monitoring equipment
Removal of SF6 gas to zero pressure on the gas zone to be dismantled
Dismantle of the connector cover to expose main conductors and completion disconnection
Further dismantle of the main connector and replacement of multiple gaskets with new EPDM gaskets
Application of sealants on all gaskets and greases via injection nipples for flange connections
Reassembly of the connector set and application of external sealants and Tor-Wax
Re-filling of gas zone using recycled gas and new gas to replace that lost through original leaks
Use of gas detection equipment to inspect for leaks and ensure integrity of the remedial works
Refilling of adjacent gas zones from half to full pressure and completion of gas handling documentation
Follow-up testing of the SF6 to ensure oxygen content and dew point are suitable for operation
Review and transmittal of all SF6 gas handled as per legal requirements; recycled, new and disposal

Due to the nature of the works additional QA procedures were implemented to ensure the integrity of the system, such as purging with nitrogen to eliminate ingress of moisture during the completion of works, ductor testing of conductors and cleaning of components using isopropyl alcohol.


“Overall it was an excellent job and the work scope was extended threefold during the program and TP Power services still managed to complete the works in time…… engineers worked the Easter weekend including bank holidays to keep the task on schedule. I would have no hesitation in recommending TP Power Services to others both within our company and externally”

Derren Wickes – EC&I Section Engineer
KPI Score Awarded: 93%