Reassessing TOV Risk: Why Developers Can’t Ignore the Hidden Impact of NOGRR245

As renewable penetration accelerates and inverter-based resources (IBRs) become foundational to grid operations, evolving interconnection standards are forcing developers to revisit long-standing design assumptions. Updates such as ERCOT’s NOGRR-245 and IEEE 2800 are redefining fault ride-through (FRT) expectations by requiring IBRs to remain connected for longer periods of time during abnormal grid conditions. While these extended ride-through windows enhance overall system stability, they also introduce a critical and often overlooked vulnerability: increased exposure to Temporary Overvoltage (TOV) conditions.

Unlike transient lightning surges, TOVs are sustained voltage rises triggered by events such as ground faults, load rejections, or switching operations. As IBRs remain online during these disturbances, they can inadvertently extend the duration of elevated voltage conditions. Surge arresters – designed to absorb brief overvoltage events – are now being subjected to prolonged energy absorption, leading to thermal stress, premature aging, and increased risk of failure. These issues are no longer theoretical; they are emerging in real-world projects. 

The push for longer FRT durations is fundamentally reshaping protection coordination. While inverters may be built to withstand prolonged overvoltages, associated equipment often is not.  

The industry can’t afford to treat surge protection as a static calculation. With FRT windows stretching beyond previous norms, updated TOV studies are no longer optional —they're essential. Without them, developers risk underestimating stress on key equipment, compromising both reliability and project bankability. 

At EPE, we help clients navigate these emerging risks. Our TOV restudy services provide the technical foundation to optimize protection coordination, extend equipment life, and ensure regulatory alignment. 

As IBR developers adapt to new grid codes, now is the time to ask: Is your system truly prepared for what NOGRR-245 demands? Even if you think it might be, contact a member of our team below to help ensure your project’s compliance.