220/132/33/11 kV Substation Augmentation at New Khimti, Ramechhap

Overview

The project was executed for the Nepal Electricity Authority (NEA) under the Ramechhap Garjyang Khimti 132 kV Transmission Line Project to augment the 220/132/33 kV New Khimti Substation in Ramechhap. Awarded under Contract No. RGK-75/76-02 (ICB) and signed on 10 March 2020, the scope covered the design, supply, construction, installation, testing and commissioning of a 220 kV GIS bay extension, additional 132 kV air-insulated bays, new 33 kV and 11 kV indoor vacuum switchgear systems, and the transformers, protection, automation and auxiliary systems required to operate them. The work was carried out by the Mahavir Shree International - CHINT joint venture and funded by the Government of Nepal. A 132 kV line bay at Lamosangu Substation was included in the associated interconnection works. Nepal Electricity Authority issued the operational acceptance certificate on 9 July 2024.

Scope & Deliverables

• Extension of the 245 kV GIS: two sets of three-phase, 3150 A, 40 kA SF6 gas-insulated busbars and one 245 kV, 40 kA ICT feeder bay module for the 220/132 kV, 200 MVA autotransformer bank, supplied by GE India, with UHF partial discharge sensors, gas monitoring devices and local bay control cubicles
• 245 kV, 1600 A, 40 kA single-phase SF6 gas-insulated bus duct (250 m) outside the GIS hall with support structures, SF6/air bushings, 245 kV overhead conductor and associated gantry structure
• Extension of the 132 kV AIS: three transformer bays on a double main busbar, comprising 145 kV, 31.5 kA circuit breakers (one 1600 A and two 800 A), nine group-operated isolators, multi-ratio current transformers, ten 120 kV surge arrestors, lattice take-off and gantry structures and equipment support steelwork
• Four 66.66 MVA, 220/root3 - 132/root3 kV single-phase autotransformers (one 200 MVA bank plus one spare unit) manufactured by CHINT, China, with digital RTCC panels, OLTCs, online insulating oil drying and dissolved gas monitoring systems and 20 kL oil storage tanks
• Two 30 MVA, 132/33 kV and one 6/8 MVA, 33/11 kV three-phase power transformers with on-load tap changers and digital RTCC facility, supplied by Schneider, India
• 36 kV indoor vacuum switchgear: eight 33 kV bays comprising two transformer incomer modules, one transformer feeder module, five line feeder modules, a bus sectionaliser and two busbar PT modules, supplied by Siemens, India
• 12 kV indoor vacuum switchgear: four 11 kV bays comprising one transformer incomer module, three line feeder modules and a busbar PT module, supplied by Siemens, India
• XLPE-insulated copper cable supplied by KEC, India, with terminations and jointing kits: 132 kV 1C x 1200 sq. mm (550 m), 33 kV 1C x 800 sq. mm (260 m) and 1C x 400 sq. mm (950 m), and 11 kV 1C x 400 sq. mm (80 m) and 1C x 240 sq. mm (400 m)
• Relay and protection panels for all voltage levels, including 245 kV duplex and 145 kV simplex circuit breaker and transformer protection panels, and augmentation of the existing Siemens low-impedance busbar protection for the 220 kV and 132 kV ICT bays
• Substation automation system to IEC 61850 covering one 220 kV, three 132 kV, eight 33 kV and four 11 kV bays, with bay control units, operator workstations, integration with the existing New Khimti automation system and integration with the SIEMENS SINAUT Spectrum SCADA at the Load Dispatch Centre, Kathmandu
• Fire protection: HVW spray systems for the 220/132 kV autotransformer units and the 30 MVA and 6/8 MVA transformers, hydrant system, pump house augmentation, smoke and fire detection and alarm systems, and portable extinguishers
• Auxiliary systems: LT AC/DC switchgear and battery and battery charger augmentation, air conditioning and ventilation for the GIS and 33/11 kV switchgear halls, indoor and outdoor illumination including switchyard and street lighting, earth mat augmentation inside the GIS building and outdoor yard, SDH STM-4 fibre-optic communication panel augmentation, and visual monitoring system augmentation
• Civil works: construction of the 33/11 kV indoor switchgear building, transformer foundations with jacking pads, rail tracks, oil soak and sump pits and fire-resistant walls, tower and equipment support foundations, cable trenches and crossings, 90 MT lattice and 15 MT pipe steel structures, and external water supply arrangements
• 132 kV line bay at Lamosangu Substation, comprising a 145 kV, 2000 A, 31.5 kA SF6 circuit breaker, group-operated and single-pole isolators, 1200 A multi-ratio current transformers, capacitive voltage transformers, 120 kV lightning arrestors with surge counters, lattice take-off gantry and equipment support structures, an SAS-compatible line control and relay panel, earthing materials and control cabling

Outcome

All bay equipment, relay panels and the SCADA interface across the 220 kV, 132 kV, 33 kV and 11 kV systems were tested and commissioned by Mahavir Shree International's technical team with NEA project staff participating and Employer representatives witnessing the tests. Pre-commissioning testing covered the circuit breakers, current transformers, capacitive voltage transformers, disconnecting switches, lightning arrestors and the 220/132 kV, 132/33 kV and 33/11 kV transformers; substation automation commissioning included configuration and verification of bay control unit inputs, outputs, measurement signals and time synchronisation. The same erection, cable termination and pre-commissioning works were completed at Lamosangu Substation. Nepal Electricity Authority issued the operational acceptance certificate on 9 July 2024, and the commissioned systems and spares were handed over to the project office for commercial operation.