NERGS-III revised: Kaying to replace Naying as pooling station
Author: PPD Team Date: 14/07/2025
The pooling station for evacuating 426 MW from Heo and Tato-I hydro projects in Arunachal Pradesh has been shifted from Naying to Kaying due to land constraints, according to a revised plan under the North Eastern Region Generation Scheme-III (NERGS-III).
NERGS-III is a transmission scheme to evacuate power from NEEPCO’s Heo (3×80 MW) and Tato-I (3×62 MW) hydroelectric projects located in Shi-Yomi district. The original plan included a 400/220 kV pooling station at Naying, a 400 kV switching station at Niglok, and a 400 kV double circuit transmission line to Gogamukh. Dedicated 220 kV lines from the generation sites were to connect to the Naying pooling station.
However, during detailed site engineering and land surveys, Central Transmission Utility (CTU) found that the proposed site at Naying was not viable due to the unavailability of suitable land. The pooling station has now been relocated to Kaying. The new location at Kaying has now been finalised, though ISTS (Inter-State Transmission System) connectivity approval is still pending.
The revised configuration will include a 400/220 kV GIS (Gas Insulated Substation) pooling station at Kaying with two 500 MVA interconnecting transformers, two 80 MVAr bus reactors, and future bays for expansion. A 100 km long 400 kV double circuit line will connect Kaying to Niglok. Niglok will operate as a switching station and has provision for a ±800 kV, 6000 MW HVDC terminal in the future.
From Niglok, a 125 km 400 kV double circuit line will extend to Gogamukh. This substation is being developed under a separate project and is expected to be commissioned by November 2026.
Under the revised NEEPCO scope, the 220 kV dedicated transmission line will now run from Tato-I to Kaying. One circuit will be looped into the Heo switchyard. Both hydro stations will also accommodate 50 MVAr, 245 kV bus reactors. All new lines must be rated to carry at least 1840 A per circuit.
CTU has clarified that intra-state construction power arrangements cannot be used for power evacuation. NEEPCO agreed to this. Additionally, GRID-India stated that synchronous condenser mode is required for hydro units over 50 MW. NEEPCO agreed to implement this if technically feasible.
While the revised plan increases infrastructure length and project cost, it maintains long-term grid stability and system feasibility. The target commissioning date for the entire NERGS-III scheme remains 28 February 2029.