Grid stability concerns intensify at major ISTS renewable hubs

The National Committee on Transmission (NCT) reviewed emerging grid stability issues at its 38th meeting, with GRID-India highlighting persistent and worsening challenges at India’s largest inter-state transmission system (ISTS) connected renewable energy complexes. Low short circuit ratio (SCR) conditions across key locations in Rajasthan and the Western Region are leading to daily oscillations that are increasingly difficult to manage in real-time operations.

GRID-India’s assessment identified four distinct types of oscillations affecting the grid. Low-frequency voltage oscillations in the range of 0.1–0.2 Hz were linked to variations in power plant controller (PPC) response times. High-frequency oscillations between 3.5–7 Hz were associated with reduced gain settings in static synchronous compensators (STATCOMs). Sub-synchronous oscillations in the 8–20 Hz band were observed even at low generation levels when SCR declined due to transmission outages. In addition, large voltage dips of 80–90 kV were recorded during periods of high renewable energy (RE) generation combined with insufficient dynamic reactive support.

Five case studies from January and February 2026 demonstrated the severity of these issues. On January 14, nine extra high voltage (EHV) transmission lines in Rajasthan tripped within 30 minutes due to kite flying and over-voltage conditions. This led to oscillations that intensified when STATCOMs reduced gain in response to hunting detection. On February 4, an inter-area oscillation event accompanied by a significant voltage dip spread across regions, with synchronous generators in distant areas reporting hunting. The event also revealed limitations of the interim STATCOM dead-band approach, which reduced oscillation amplification but weakened dynamic reactive support, complicating voltage control.

A planned outage of the 400 kV Bikaner (PG)-Bikaner-II double circuit (D/C) line from February 22–23 for line-in-line-out (LILO) works at the upcoming Bikaner-III substation provided further insight. During the outage, fault level at Bikaner-II dropped sharply from 17,134 MVA (SCR 4.42) to 6,870 MVA (SCR 1.77). Persistent oscillations around 20 Hz continued despite multiple interventions, including STATCOM mode adjustments, selective disconnection of RE plants, STATCOM switching, and high voltage direct current (HVDC) Balia-Bhiwadi switching. Stability improved only after at least one circuit was restored. GRID-India observed that inverter-based resources faced difficulty remaining connected even at low generation levels under such reduced fault conditions.

Recommended measures and system planning approach
GRID-India indicated that adding transmission lines alone will not materially improve fault levels at these complexes, and SCR is likely to decline further with capacity additions. Proposed measures included early commissioning of synchronous condensers or similar devices, faster implementation of planned evacuation infrastructure, detailed root cause analysis and controller tuning for RE plants and STATCOMs, pilot deployment of grid-forming inverters, standardisation of PPC settings through regulatory notification, and strengthening of reactive compensation within Rajasthan’s intrastate network.

Expert Member S.R. Narasimhan recommended that the Central Electricity Authority (CEA), Central Transmission Utility (CTU), and GRID-India jointly define functional requirements for grid-forming inverters ahead of formal standard updates. A target of 10–15% penetration of grid-forming inverters at solar plants was suggested to support field-level validation. Central Transmission Utility of India Limited (CTUIL) has been directed to prioritise planning for synchronous condenser deployment and to convene discussions with original equipment manufacturers (OEMs) on pilot implementation of grid-forming solutions.

The featured photograph is for representation only.