Service continuity criteria for gas insulated switchgear (GIS) - Utility experience in green field and brown field GIS substations

Global industrialization & increasing population results in rise of demand for quality and uninterrupted power-supply. To achieve this, Substation equipments have to be made more efficient & reliable to cope up with increasing demand. Moreover, shortage of geographical area needs creation of compact but efficient power-supply medium. Hence, Gas Insulated Substation (GIS) is the right solution to address the above stated attributes. Gujarat is one of the prosperous states of India where power requirement has grown steadily in all segments.

Recently, peak power demand has reached to 24544 MW in comparison to 12348 MW in 2012-13. To mitigate-the solution, GETCO has no option other than creating Gas Insulated Switchgear (GIS) substation as a Green-field or Brown field substation by uprating & expanding existing substation due to space constraint. In view of above, Gujarat Energy Transmission Corporation Ltd (GETCO) has adopted 33 kV to 400 kV Gas Insulated Switchgear (GIS) technology due to its excellent features like compactness and maintenance free switchgear as compared to Air Insulated Substation (AIS). However, availability & service continuity of GIS substation is the main concern for any power utility during Maintenance, Repair & Extension (MRE) or on site dielectric testing of GIS.

MRE procedure for GIS is much more complicated due to its compact design and installation within restricted space. All these activities are challenging for any utility since it includes gas work, dismantling the equipment to be inspected and high-voltage test prior to re-energization. Moreover, there is no complete awareness of how to dismantle faulty Gas Compartment without disturbing other bays in limited time frame with safety considerations-for different GIS make. Hence, it is always recommended that maintenance/repair/extension activities should be carried out with specific safety measures by qualified & experienced personnel and as per defined Method-of Statement (MOS) for safety of equipment and personal.

In view of above, improper or inadequate design of GIS can endanger personnel and may lead to failure of various components of equipment. In certain cases, long shutdown is required for maintenance which is not-permissible as well as affordable to utilities. Therefore, GIS should be designed in a way to achieve maximum-service continuity and personnel safety during both normal operating and maintenance conditions.

As observed, by not defining Service Continuity Criteria requirement in Technical Specification, GIS OEM offers-simpler design as per their standard practice which ultimately require longer shut downs and in certain cases, complete substation shutdown in case of MRE activities. Hence, service continuity requirements /criteria by users/utilities during purchase /tendering stage shall be well defined for all activities (i.e. maintenance, repair, extension and HV test) and same shall be identified by OEMs during quotation phase to accomplish users requirement and transparent discussion to avoid loopholes in specification for satisfying users expectation.

The full-length paper covered the importance of defining service continuity criteria in specification. In addition, also addressed various factors for improving service continuity criteria for MRE activities and how GIS design-was modified to achieve the expectation of users. For this various case studies have been presented to demonstrate advantages of introducing service continuity criteria/requirement. This way, utility can achieve-higher reliability ensuring safety of personnel as well as equipment.