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Regulators press utilities on monitoring gaps after Broad Brook relay and data limitations
Summary
Authority staff and parties identified gaps: event-triggered relays with finite memory, production meters with coarse granularity, and the site’s lack of the new DER gateway standard — and discussed short-term POI monitoring and a one-month power-quality study to detect harmonics or transients.
Authority staff sought detailed answers on how commissioning tests, relays and meters record power-quality data and whether that data would have captured pre-event conditions before the March and July incidents.
Eversource engineers explained that protective relays and reclosers operate and generate alarms only when specific thresholds are met; relay waveform captures are event-triggered and limited by available memory. Next ERA said their production meter records power, reactive power and power factor continuously but at a much coarser interval (typically one to five minutes), and that relay waveform captures are only available when a relay operates and downloads event files.
Eversource told the panel that the DER monitoring gateway is a recent interconnection standard and the Broad Brook project, which was commissioned earlier, does not have a gateway; the company said retrofitting existing sites lacks a straightforward mechanism because it would impose cost and commissioning burdens on owners. Parties discussed short-term options: installing a power-quality meter at the point of interconnection or at an upstream transformer for an observation period (panelists suggested around one month) to look for harmonics, transients or other low-level events a relay might not record.
RMS Energy's root-cause report and Next ERA's site inspections also flagged memory limitations in relay recordings: RMS reported the earliest available waveform it reviewed began at 1:55 a.m. on March 8 and indicated older event captures may have been overwritten. Eversource and Next ERA agreed that relay settings and recording behavior could allow some short-duration or small-magnitude anomalies to go unlogged unless they caused device operation.
Participants agreed to next steps: Eversource will evaluate and, where appropriate, deploy targeted power-quality monitoring and will supplement the record on historic events per the Authority's interrogatory schedule. The panel discussed working with inverter manufacturers or independent third parties to validate inverter configurations and to scope any inverter-level testing that may be required before re-energization.
