Full Report
In January 2026, a technical incident occurred in Estonia during testing of the new 100MW Hertz 1 (Kiisa) battery energy storage system (BESS). The event triggered protective relays, resulting in the emergency shutdown of over 1GW of HVDC capacity, specifically the EstLink 1 and EstLink 2 interconnectors. The root cause was an incorrect parameter configuration […]
Analysis Summary
# Incident Report: HVDC Outage Due to BESS Parameter Misconfiguration
## Executive Summary
In January 2026, testing of the new 100MW Hertz 1 (Kiisa) Battery Energy Storage System (BESS) in Estonia led to a widespread grid disturbance. An incorrect parameter configuration in the BESS inverters caused low-frequency network oscillations, triggering protective relays and resulting in an emergency shutdown of over 1GW of HVDC capacity across the EstLink 1 and EstLink 2 interconnectors between Estonia and Finland. The issue was technically resolved by adjusting inverter response settings.
## Incident Details
- Discovery Date: January 2026 (During system testing)
- Incident Date: January 2026
- Affected Organization: Operators of the EstLink 1 and EstLink 2 interconnectors (Implied: Estonian and Finnish grid operators)
- Sector: Energy / Electrical Power (Grid Infrastructure)
- Geography: Estonia
## Timeline of Events
### Initial Access
- Date/Time: January 2026 (During testing)
- Vector: **Technical/Configuration Error (Not Cyberattack)**
- Details: Testing commenced on the 100MW Hertz 1 (Kiisa) BESS.
### Impact Progression
- Date/Time: Immediately following deviation
- Vector: Incorrect inverter configuration
- Details: Incorrect parameter configuration in the BESS Nidec Conversion grid-forming inverters induced low-frequency network oscillations. Feedback gains in the Virtual Synchronous Machine (VSM) controls were set too sensitively, amplifying disturbances instead of damping them.
### Detection & Response
- Date/Time: During the event
- Vector: Protective relay activation
- Details: The oscillations triggered protective relays, forcing the emergency shutdown of the associated grid protection systems. Over 1GW of HVDC capacity (EstLink 1 and EstLink 2) was taken offline.
- Response actions taken: The issue was resolved by **increasing response delays and tuning down the feedback gain coefficients** of the inverters.
## Attack Methodology
*Note: This incident was a technical failure during testing, not a malicious cyberattack, thus traditional MITRE ATT&CK categories do not fully apply. The 'vector' here describes the technical control failure:*
- Initial Access: Testing initiated on BESS equipment.
- Vector of Impact: Incorrect configuration of control algorithms (VSM feedback gains).
- Impact: Inducing physical instability (low-frequency network oscillations) leading to cascading protective shutdowns.
## Impact Assessment
- Financial: Not specified, but significant due to loss of interconnectivity capacity.
- Data Breach: None. This was an operational stability incident.
- Operational: **Severe.** Emergency shutdown of over 1GW of HVDC capacity across the EstLink 1 and EstLink 2 interconnectors, disrupting power exchange capabilities between Estonia and Finland.
- Reputational: Demonstrated a critical theoretical vulnerability in a physical setting.
## Indicators of Compromise
*Not applicable in the traditional sense, as no external intrusion occurred. The indicators are operational parameters:*
- Behavioral indicators: Excessive sensitivity in feedback gains; amplification of low-frequency network oscillations.
## Response Actions
- Containment measures: Protective relays functioned as designed to isolate the unstable segment.
- Eradication steps: Immediate isolation of the faulted BESS unit or system adjustments.
- Recovery actions: Reconfiguration of the BESS Nidec Conversion inverter settings (increasing response delays, reducing feedback gain coefficients).
## Lessons Learned
- Theoretical vulnerabilities regarding inverter-dominated grids (IBRs) are now a physical reality at utility scale.
- Control system settings, particularly feedback gains in VSM algorithms, must be rigorously tested and highly constrained due to their potential to destabilize bulk power systems.
- High-capacity, grid-forming BESS inverters require protection and safety standards equivalent to nuclear or aviation control systems.
## Recommendations
- Implement stringent, validated testing protocols for all control parameters on grid-forming inverters before connection to transmission grids (e.g., ENTSO-E connections).
- Establish stringent safety standards and regulatory oversight specifically tailored to the dynamic stability risks posed by high-capacity IBRs.
- Review and potentially mandate reduced sensitivity or inherent limitations on feedback gains in VSM control loops to prevent self-induced instability.