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Protection System Misoperations

​​​​​​​​​​​​​Protection System Misoperations (Misoperations) are a key risk facing the Bulk Power System and remain an area of focus in the industry. Misoperations are defined as “the failure of a Composite Protection System to operate as intended for protection purposes." Misoperations include a Protection System's failure to operate, slowness in operating, or operating when not required during either ​a fault or non-fault condition. 

Misoperations contribute to, and tend to exacerbate the impact of, automatic transmission outages, which adversely affect the reliability of the BES. Included below are several ReliabilityFirst Misoperations Analysis documents, which provide summaries of Protection System issues, details and corrective actions associated with those issues, and lessons learned.​

Misoperation Metrics

NERC gathers Misoperation data from Registered Entities of the Electric Reliability Organization (ERO), which consists of NERC and the Regional Entities, on a quarterly basis by a NERC Rules of Procedure Section 1600 Data Request. The ERO analyzes this data for trends in Misoperations. Below are key metrics monitored by the ERO and RF.

ERO Misoperations, Operations Rate for 2021 ERO Misoperations-Operations Rate for 2021.png

ERO charts are developed on a calendar-year basis. Results in the NERC State of Reliability report are on a Q4-Q3 basis.

ERO Misoperations by Cause Code 2018-2021

ERO Misoperations by Cause Code 2018-2021.png

RF Misoperations, Operations, Rate 2018-2021

RF Misoperations Operations Rate 2018-2021.png

RF Misoperations by Cause Code 2018-2021

RF Misoperations by Cause Code 2018-2021.png

Recent NERC Lessons Learned

LL20220405 Consequences of Altering Protection System Wiring for Failing CCVT

LL20210802 Multiple Faults Contribute to Relay Misop Load Loss 

LL20210203 Transient Induced Misoperation Approach I 

LL20210204 Transient Induced Misoperation Approach II 

LL20200703 Lockout Relay Component Failure Causes Misoperation and Reportable Event

Unnecessary trips for non-fault conditions are problematic for any protective relay and can be particularly problematic for lockout relays. Lockout relays are typically used to isolate and hold BES electrical equipment out of service for extended periods of time to allow for visual inspection and typically result in the operation of multiple interrupting devices. The resulting extended abnormal operating condition of the system may put the reliability of the BES at risk.


LL20200702 Verification of AC Quantities during Protection System Design and Commissioning

Failure to employ effective commissioning testing practices or effective quality checks of protection system designs when installing or modifying protection systems can lead to Protection System Misoperations. These can occur with all components of Protection Systems, but issues with voltage and current instrument transformer wiring regularly surface when Protection System Misoperations occur. Protection System Misoperations have an immediate negative impact on the reliability of the bulk power system and may cause a significant increase in the magnitude and scope of a disturbance.


LL20200701 Mixing Relay Technologies in DCB Schemes

Multiple Composite Protection System Misoperations have occurred on the Bulk Electric System (BES) as a result of mixing protective relay technologies at the remote terminals of directional comparison blocking (DCB) schemes. One of the most challenging mix of technologies is utilizing a relay system based on newer microprocessors (µP) at one terminal and an older electromechanical (EM) relay system at the opposite terminal. Utilizing different models of µP based relays at each terminal can also be problematic. Often, only one terminal of a DCB system is upgraded to µP based relays due to various reasons, including different ownership of terminals, budget constraints, and emergency replacements. Relay timing and directional coordination is critical in DCB schemes that may be overlooked when relay technology or relay models vary between terminals.

All NERC Lessons Learned are published here on the NERC website.​