Authored by: Jared Vochoska, Transmission Planning Engineer

At this year's ESIG Spring Conference, grid planners convened in Arizona to tackle emerging themes: Inverter-based resources are proliferating faster than models can reliably capture their behavior, data centers are showing up as a first-class stability problem, and the shifting policy landscape is resulting in more transmission despite remaining gaps. This article covers five themes that defined the conversation: the push to scale up EMT studies, growing concerns around dynamic behaviors and IBR control interactions, emerging convergence in data center interconnection requirements, and WestTEC's first-of-its-kind effort to establish a WECC-wide long-term transmission planning process.

EMT Modeling

IBR penetration and data center growth necessitate EMT modeling, especially in weak systems. There was strong support for a shift toward screening and staged assessment — not "full EMT for everything." The proposed multi-stage approach moves from a passive frequency scan to targeted POC injection testing, with full EMT reserved for confirmed hotspots.

There was in-depth discussion around screening methods. SCR is no longer sufficient as more IBRs are interconnected — their dynamic, frequency-dependent impedance needs to be captured. Impedance-based approaches (IBSA / impedance scans) and newer metrics (e.g., NSCR concepts) are aimed at capturing network and inverter interaction effects that SCR alone misses.

The Model-Reality Gap

Mismatches between models and real-life behaviors were a recurring concern. BESS fast frequency response can be too fast in practice — aggressive response times in low-inertia grids create a negative feedback loop that standard simulation practices fail to expose. There's also an unresolved tension between UDMs and generic models: generic models don't accurately reflect real-world behavior the way UDMs can, but no clear industry consensus has emerged on widespread UDM adoption.

The practical guidance offered was to ask for tuning manuals from OEMs and confirm explicit parameter adjustability ranges — with iterative back-and-forth so that study settings correspond to field-implementable settings.

Data Centers

Data centers are now a first-class stability problem. Rapid ramps, unpredictable load profiles, and synchronous machine mechanical risk were all connected to grid stability concerns. Utility and ISO discussions emphasized gaps in industry-wide requirements, with emerging requirements around ride-through, power quality, harmonics, ramp limits, monitoring, and modeling. A notable thread was the need for functional standards for large loads (FERC / NERC discussions), since many regions are currently building ad hoc requirements.

On flexibility, consensus was that load flexibility to enable quicker interconnection would be ideal for both parties — but operators want 100% commitment to flexibility from datacenters, who want speed and incentives. Loads haven't historically been planned under a flexible framework, although DR has existed, and this would require a new class of load in the study process. Classic "economic DR" is not compelling for large AI loads — they earn significantly more money by running their facility. A more plausible lever is interconnection priority / speed in exchange for credible flexibility commitments (depth, speed, duration, availability).

WestTEC — Western Transmission Expansion Coalition

WestTEC is industry-led and close to comprehensive across utilities and developers, which makes it a credible venue for aligning on needs. The work is the first of its kind: a WECC-wide 10- and 20-year transmission study identifying where load, generation, and inter-regional transfers are growing faster than the transmission system. WestTEC’s scope includes thousands of miles of new lines and upgrades and a tens-of-billions investment envelope.

One caveat— WestTEC is only identifying transmission needs, not defining the pathway to get those projects approved, funded, or built. After the studies, all identified upgrades will still require sponsors, stakeholder support, and a plan for cost allocation. Net: WestTEC seems like one of the most concrete mechanisms currently pushing WECC toward something closer to a shared regional planning process, but it still requires more work by the stakeholders before the benefits are realized.

Order 1920

FERC Order 1920 requires planners to evaluate transmission benefits across 7 metrics. The benefits list is broad, and a single model is unlikely to capture all of them. Open questions remain around reference cases, double counting, and monetizing traditionally un-monetized benefits. CAISO, NYISO, and MISO all said that their existing processes largely align with O1920 already. The prevailing view is that O1920 will result in more transmission getting built, since there will be a better framework to evaluate and justify proposals.