The proposal of building what could be India’s first “Green GIS” switching station on the ISTS network will be deliberated by the National Committee on Transmission (NCT) in its next meeting.
This plan has been under discussion at various regional committees since November 2022 and will now be deliberated upon at the next NCT meeting scheduled later this month. Interestingly, NCT has discussed this scheme in at least two meetings last year but deferred its final decision. (Details presented ahead)
The green switching station will be part of an ISTS scheme called “North Eastern Region Expansion Scheme – XXI, Part B” or “NERES-XXI, Part-B” and will mainly involve converting the existing 132kV Badarpur switching station (AIS) to “Green GIS”.
Owned by Power Grid Corporation of India Ltd (PGCIL), the 132kV Badarpur switching station is located on NH-44 in district Hailakandi in Assam, and helps evacuation from power generation plants in Assam, such as Pallatana and Bongaigaon.
Rationale
The Badarpur switching substation was commissioned way back in 1999 and will be completing 25 years of service this year. PGCIL has notified that it was facing issues in operations & maintenance (O&M) of this switching station. The Central PSU had also suggested upgrade of the switching station from the current “single main bus transfer” scheme to “double main bus transfer scheme.” PGCIL had also recommended converting it from AIS to GIS.
It was later felt that in line with the philosophy of adopting newer and cleaner technology, the GIS (gas insulated switchgear) could be of the “green” type.
A “green” GIS would mean using of eco-friendly substitutes for the conventional SF6 (sulphur hexafluoride) gas that is known to be a greenhouse gas with detrimental ecological implications.
SF6 alternatives
According to information available with T&D India, several developed nations have pledged to go SF6-free, in alignment with their carbon-neutrality goals. Leading equipment suppliers like Siemens, Hitachi, ABB, GE and Eaton, to name a few, are actively working on SF6-free technology in switchgear. Some alternatives to SF6 that are currently being developed include a combination of vacuum interruption technology and clean air (as seen in switchgear products launched by Siemens under its “Blue” portfolio; see picture) or a fluoronitrile-based gas mixture that is under development by a partnership of GE and Hitachi. Eaton is also believed to have “solid insulated switchgear” that has no insulating material, be it SF6 or any other gas or even air for that matter.
AIS versus GIS
Speaking to T&D India over phone, Praveen Gargava, Chief Engineer, Madhya Pradesh Power Transmission Company Ltd (MPPTCL), explained that a switching station differs from a substation in that a switching station has no transformer and therefore does not change the system voltage. Gargava noted that converting the AIS switching station to the GIS variety will entail dismantling of the entire AIS ecosystem that comprises isolators, breakers, relays, etc, and replacing it with an integrated gas-insulated switchgear (GIS). The land saving from this conversion is very significant as GIS needs less than 40 per cent of the land required for an AIS-based station. Praveen Gargava also observed that due to this land-saving aspect, MPPTCL is also going in for GIS substations, albeit the conventional ones using SF6 gas, at least for now. All the same, the state utility is very proactive in scientifically monitoring SF6 leakage as fugitive emissions of SF6 can have extremely dangerous ecological implications, Gargava cautioned.
Scheme details
“NERES-XXI, Part B,” the ISTS scheme entailing the Green GIS will be officially termed as “Upgradation of single main & transfer bus to double bus arrangement with Green GIS at 132kV Badarpur (POWERGRID) switching station along with upgradation of necessary control, protection, communication, automation & LT auxiliary system.”
The scheme is expected to cost Rs.110 crore and is envisaged for completion in 30 months. NCT’s deliberations on the scheme will also include a decision on the mode of implementation – whether TBCB (tariff-based competitive bidding) or regulate tariff mechanism (RTM).
Previous NCT meetings
It is interesting to note that this scheme had come up for deliberations at an earlier meeting of NCT, held in August 2023. It was then felt that since the average life of a switching substation is generally 35 years, there should be ascertainable reasons for replacing the 132kV Badarpur substation within 25 years. After detailed deliberations, NCT decided to review the scheme at a later date.
The scheme was once against discussed at the NCT meeting in November 2023 where it was decided to defer the scheme at present, and take it up after more discussions on “green technology” that would touch upon aspects like advantages of Green GIS, availability of Green GIS vendors in India, cost implication of converting conventional AIS to Green GIS, etc.
The ensuing NCT meeting will therefore be very crucial in charting the future course of India’s first “Green GIS” on the ISTS network.
Featured photograph showing a switching station is for representation only
