Regulators probe root causes and monitoring gaps after Broad Brook solar facility incidents

Vice Chairman David Arcante opened a technical session in docket 25311 to review recurrent equipment failures at the Broad Brook solar facility and to consider monitoring and remediation measures to ensure safe re-energization.

The meeting reviewed filings and root-cause analyses that Eversource and Next ERA submitted after incidents in March and July 2025 and an apparent bird strike reported in August 2025. "The community have a right to feel safe," Vice Chairman David Arcante said, framing the proceeding as focused on both technical causes and public-safety outcomes.

Authority staff questioned Eversource and Next ERA about the facility's interconnection, the commissioning and periodic interconnection tests, and how event and waveform data are collected and retained. Eversource described the site as composed of three points of interconnection — two POIs at 2 MW AC and one POI at 1 MW AC — that coalesce before the Eversource point of interconnection. Eversource representatives said developers prepare and perform witness/commissioning tests and submit the results for Eversource review against its basic interconnection requirements; detailed design validation, they said, depends on the developer's professional engineer.

A central technical concern was how power-quality events are detected and recorded. Eversource staff explained that alarms at the isolating device (a recloser) occur only when the device operates; recorded logs document deviations generally flagged at roughly ±5% of nominal voltage at that device. Relay waveform captures are event-triggered and limited by in-device memory, and production meters provide continuous power and reactive-power values at coarse granularity (typically 1–5 minute updates). As a result, participants said low-level or very short-duration sags, transients or harmonics could go unrecorded unless the relay tripped or a customer complaint prompted investigation.

Next ERA described the independent root‑cause analysis conducted by RMS Energy. RMS combined site inspections, relay/event download review and repair logs, and reported that earliest available event waveform data began at 1:55 a.m. on March 8, with earlier event records likely lost because relay event buffers were full. The RMS report cited a wiring failure in metering equipment (an indoor switchboard) and later flashover/carbonization as proximate causes for an August trip; the parties discussed whether some trips could also have arisen from transient utility-side switching events that would not have triggered Eversource alarms.

Participants discussed remediation and data-collection options. Eversource said the current interconnection standards now include a DER monitoring gateway for new projects but that the Broad Brook site was commissioned before that requirement and does not have a gateway. Eversource offered to deploy targeted power-quality monitoring at the point of interconnection or upstream transformer for a short observation period (for example, about one month) to capture harmonics or transients; party representatives estimated a month to scope inverter-level testing or a plan to gather inverter telemetry, whereas POI-level monitoring could be deployed more quickly.

Eversource also agreed to supplement the record on historic events and per-site event counts. Authority staff said additional interrogatories will be issued and that companies should provide the requested data and any proposed monitoring/remediation plans.

The Authority set tentative next procedural dates and adjourned. The record shows the parties identifying monitoring gaps, relay-memory limits, and wiring damage on site as the main technical issues to resolve before any decision on re‑energization.