Misoperations

Transmission equipment such as relays are used to prevent situations that can lead to an outage or loss of transmission lines and infrastructure. The inability of such equipment to respond appropriately can ultimately result in Bulk Electric System (BES) instability or failure. ReliabilityFirst (RF) concluded that Composite Protection System Misoperations (misoperations) can pose a risk to the Bulk Power System (BPS) operations under various conditions. NERC made a similar assessment in its State of Reliability Report. For the 2025-26 Regional Risk Assessment (RRA), RF ranked misoperations with a medium-high risk score.

Relays are designed to find and correct faults by isolating the portion of the fault condition and ensure continuous service. They act quickly (in milliseconds) to isolate faults by tripping circuit breakers and preventing blackout conditions. Misoperations can occur when relays do not work as intended to prevent or respond to fault (or non-fault) conditions.

NERC Protection and Control (PRC) Standards that apply to Composite Protection Systems are designed to identify and correct the causes of misoperations. Additionally, the RF Protection Subcommittee, in collaboration with registered entity members, performs support and analysis of misoperation events in the RF footprint.

Misoperations remain a significant risk in RF’s territory despite metrics that indicate performance improvement in recent years. As shown in Figure 13, total misoperation frequency and the misoperation rate have trended downward between 2020 and 2025.

Root cause analyses of these misoperations found that equipment failures (i.e., relay failures) and human performance (i.e., incorrect settings) were the leading causes of misoperations in the RF footprint during this period. Both equipment failures and human performance-related misoperations exhibited year-over-year declines.

The 138 kV voltage class makes up 47.7% of the line mileage in the RF footprint, and most of the misoperation events occurred in this voltage class. Between 2021 and 2025, misoperation frequency on 138 kV facilities trended upwards while misoperation frequency for all other voltage classes decreased (see Figure 14).

Relay failures were the main cause of misoperations in the 138 kV voltage class, and the RF Protection Subcommittee identified multiple instances of entity programs underway to replace line relays at 138 kV facilities. RF will continue to monitor this issue, including any performance improvements resulting from line relay replacement programs.

RF tracks various types of equipment impacted by protection system misoperations (e.g., lines, transformers, generators, capacitor banks). Historically, misoperations of protection relays and controls on capacitor banks have been an area of concern for RF registered entities.

The specific risk associated with capacitor bank misoperations is the loss of a voltage support device exacerbated by an additional loss of a line or transformer, which could lead to more severe consequences. Several entities within RF have proactively implemented improvements to their system infrastructure or post-event processing related to capacitor bank misoperations. Capacitor misoperation events from 2021-2025 have trended relatively flat in the RF footprint, which was consistent with a broader ERO-wide trend (see Figure 15).