Case Study: 400 kV GIS Erection at Koyna Stage IV Hydro Project
Client: ALSTOM Export (India Branch)
Location: Koyna, Maharashtra
Project Year: 1999
Sector: Transmission Infrastructure / Hydro Power
The Koyna Stage IV hydroelectric project (2 × 250 MW) required a high-reliability GIS (Gas Insulated Switchgear) installation for its 400 kV switchyard. ALSTOM Export engaged Mahati for the erection of this critical high-voltage infrastructure under their direct supervision.
The GIS system was to serve as the switching interface between power generation and the grid, making installation accuracy and reliability crucial for project success. Mahati was tasked with complete site execution, from mechanical assembly to electrical testing, for 10 complete bays of 400 kV GIS equipment.
Example of a Gas Insulated Substation done by Mahati.
Challenges and Requirements
The project scope required Mahati to manage:
On-site preassembly of GIS breakers and enclosures.
Mechanical and electrical erection of 10 GIS bays.
Routing and connection of high-voltage and low-voltage cables.
Precise integration with transformer systems.
Final testing and commissioning of HV systems.
The team had to meet strict site quality, cleanliness, and safety standards while adhering to tight timelines and international engineering protocols. ALSTOM required proof of technical competence and clean handover practices.
Mahati’s Approach & Solution
Mahati deployed an experienced erection team trained specifically in 400 kV GIS systems. Under ALSTOM’s supervision, Mahati led mechanical preassembly, cable routing, termination, and HV test execution on-site.
Solution Highlights:
Detailed erection planning, minimising downtime and rework.
Safe handling of preassembled GIS modules to prevent damage.
Testing of HV and LV connections in line with IS and IEC standards.
On-site integration with power transformers and grid tie-ins.
By breaking the scope into modular sequences, the team ensured quality control at every step without delaying downstream activities.
Implementation & Execution
Mahati implemented the project in a phased approach, ensuring zero operational disruptions:
Phase 1 – Site Preparation and Layout:
Mahati surveyed the installation zone and ensured foundations were GIS-compliant. Mechanical preassembly was carried out in designated areas to streamline bay placement.
Phase 2 – Erection and Cabling:
Each bay was installed sequentially to allow cable routing and testing in parallel. LV and HV cable trays were mapped for minimum interference. All GIS joints and SF6 compartments were secured to ALSTOM’s specifications.
Phase 3 – Testing and Handover:
Mahati conducted high-voltage testing and continuity checks across connections, including interface testing with transformers. 82% of the project was completed at the time of certification, with a clean record of safety and quality.
Results & Impact
400 kV GIS erected to full compliance with ALSTOM standards.
82% of the total project was completed within the planned duration.
GIS system prepped for commissioning with minimal punch list.
On-site quality and cleanliness rated satisfactory by ALSTOM.
The project demonstrated Mahati’s capabilities in managing large-scale high-voltage infrastructure, under international supervision, with consistency and site discipline.
Future Outlook & Scalability
The success at Koyna laid the foundation for Mahati’s GIS portfolio. The execution approach has since been scaled for AIS and GIS installations across India. Mahati remains a trusted partner for OEMs and EPC contractors seeking disciplined, high-voltage site execution.
Why Mahati?
Proven execution track record in 400 kV GIS erection.
Close coordination with international OEMs.
Trained high-voltage erection and testing teams.
On-time delivery with assured compliance to IS and IEC standards.
Mahati’s role at Koyna Stage IV marked the beginning of its journey in national-scale transmission infrastructure.