Appendix B — Glossary of · Large-Load Grid Integration

Vlad Zavadsky

doi:10.5281/zenodo.21464969

Reference

Appendix B — Glossary of Terms#

Acronyms and specialized terms used in this report, in the sense intended here.

Ancillary services: Grid support services (reserves, frequency and voltage support) that keep supply and demand balanced instant to instant; large loads may be charged for them even when co-located.
ANOPR / NOPR: Advance Notice / Notice of Proposed Rulemaking — the early and formal stages of a FERC rule, preceding a final rule.
ARM: Anticipated Reserve Margin — the cushion of expected supply over peak demand; a falling ARM signals tightening adequacy (Section 2).
BAL-002 / MSSC: NERC balancing standard and the “Most Severe Single Contingency” it sizes reserves against — the benchmark now being applied to clustered large-load loss.
BESS: Battery Energy Storage System.
BTM: Behind-the-Meter — generation or storage on the customer side of the revenue meter (Sections 5 and 8).
BYOG: Bring Your Own Generation — an expedited pathway conditioned on the load supplying incremental generation.
Capacity accreditation: The step that converts a resource’s nameplate rating into the firm capacity credited for adequacy, usually through ELCC; a load able to curtail may be accredited as a resource rather than counted only as demand (Technical Annex T.6).
Capacity market: A forward market (notably PJM's) that pays generators years ahead to be available at peak; its clearing price is a channel by which load growth reaches retail bills (Section 3).
CIR: Capacity Interconnection Rights — a generator's accredited right to sell capacity; reduced when the unit serves on-site load (Section 5).
CLR: Controllable Load Resource — an ERCOT large load that is dispatchable in the market and can be curtailed (Section 6).
CMPLDW / PERC1: The WECC composite load model (motors + electronics + DER) and PERC1, the new computational-load model that captures voltage-sensitive trip, UPS transfer, and reconnection (Technical Annex T.4).
COD: Commercial Operation Date — when a project begins commercial service.
Coincident / non-coincident peak: A load’s demand at the instant of system peak versus its own maximum whenever that falls; the gap explains why adding a megawatt of load need not raise system peak by a megawatt (Technical Annex T.5).
Co-located load: Load sited directly at a generator, drawing power without full reliance on the transmission grid (Section 5).
Curtailment-enabled headroom: The additional load an existing grid can serve if that load agrees to reduce for a limited number of hours per year — on the order of 20 to 90, depending on the curtailment level assumed (Section 6).
Diversity factor: The ratio of the summed individual peak demands to the combined peak of the same set; it falls as loads coincide, which is why high-load-factor computational campuses erode the diversity utilities have long relied on (Technical Annex T.5).
DR: Demand Response — paying or instructing customers to cut usage at peak; an alternative source of headroom to on-site generation.
DRRS: Dispatchable Reliability Reserve Service — a new ERCOT ancillary service created under Texas law.
ELCC: Effective Load-Carrying Capability — a probabilistic method for crediting how much a resource (or flexible load) actually contributes to resource adequacy (Technical Annex T.6).
EMT: Electromagnetic Transient — a high-fidelity, full-waveform simulation class needed to model power-electronic load behavior at the point of interconnection, especially at weak-grid points.
FIDVR: Fault-Induced Delayed Voltage Recovery — voltage staying depressed after a fault clears; a dynamic-assessment failure mode (Technical Annex T.8).
LOLE / LOLH / EUE: Loss-of-Load Expectation (days/yr short; standard ≤ 0.1, the “1-in-10” criterion), Loss-of-Load Hours, and Expected Unserved Energy — the probabilistic resource-adequacy metrics (Technical Annex T.6).
ProbA: Probabilistic (resource-adequacy) Assessment — Monte Carlo simulation over weather, load, and outage combinations used to compute LOLE/LOLH/EUE.
PRM / RML: Planning Reserve Margin and the Reference Margin Level it must meet to satisfy the LOLE standard (Technical Annex T.6).
RoCoF: Rate of Change of Frequency — how fast frequency moves after a sudden loss; worsens as inverter-interfaced load displaces inertia (Technical Annex T.8).
N-1 / N-1-1: Contingency criteria: the system must withstand the loss of any single element (N-1), or a single element followed by another (N-1-1), without cascading; a stricter N-2, the simultaneous loss of two elements, is applied selectively to the most critical facilities — the core of TPL-001 planning (Technical Annex T.3).
SCR / WSCR / CSCR: Short-Circuit Ratio and its weighted and composite variants — measures of local grid strength; low values flag weak-grid points where inverter-dominated loads may be unstable and EMT study is required.
TPL-001: NERC's transmission-system planning standard (currently TPL-001-5.1), defining the contingencies the system must withstand.
ZIP / static load model: A load represented as fixed or voltage-proportional constant power — the legacy model that cannot capture a load tripping during a fault (Technical Annex T.4).
ERAS / EPR: MISO's Expedited Resource Addition Study (fast-track generator interconnection) and Expedited Project Review (fast-track transmission upgrades).
Firm service: Transmission or interconnection service the grid commits to provide at all times — the opposite of non-firm/curtailable service.
FPA §201(b) / §205 / §206: Federal Power Act sections defining FERC jurisdiction (201(b)), utility-initiated rate filings (205), and Commission-initiated “just and reasonable” review (206).
Grid-following (GFL) inverter: A converter that measures grid voltage and injects current in step with it, relying on an already-stiff grid to hold its reference; the dominant design in existing inverter-based resources and in load-side power electronics (Technical Annex T.4).
Grid-forming (GFM) inverter: A converter that regulates its own voltage and phase angle, presenting to the network as a voltage source and lending system strength; increasingly required at weak points of interconnection (Technical Annex T.4).
HILL: High Impact Large Load — SPP's process (and the name of the rejected Tri-State tariff) for jointly studying a large load and its proximate generation.
Hosting capacity: The load or generation a given feeder or substation can accept before a thermal, voltage, or protection limit forces an upgrade (Technical Annex T.9).
Interconnection queue: The ordered list of pending requests to connect to the grid; large-load queues have swelled with speculative and duplicate entries (Section 1).
IRP: Integrated Resource Plan — a state-regulated utility's long-range supply plan.
Islanding: Disconnecting from the grid and running on on-site generation; when uncommanded and at GW scale it is a bulk-system disturbance (Section 8).
ISO / RTO: Independent System Operator / Regional Transmission Organization — operators of organized wholesale markets (PJM, MISO, SPP, CAISO, ISO-NE, NYISO; ERCOT is an ISO outside FERC jurisdiction).
LAR: Load Adjustment Request — PJM's framework for vetting large-load additions before they enter the forecast (Section 1).
LSE: Load-Serving Entity — the entity responsible for supplying an end-use customer.
LTRA / LTLF: NERC's Long-Term Reliability Assessment and PJM's Long-Term Load Forecast — the principal ten-plus-year outlooks cited here.
NITS: Network Integration Transmission Service — the default full-service (firm) transmission product.
Non-firm service: Interruptible transmission or interconnection service, generally faster and cheaper than firm service (Sections 6 and 8).
PGRR / NPRR / NOGRR: ERCOT Planning Guide / Nodal Protocol / Nodal Operating Guide Revision Requests — the protocol-change instruments (e.g., PGRR145, NPRR1325).
Protection coordination: The timing sequence by which relays and breakers isolate a fault at the smallest affected zone; large inverter loads complicate it through fast undervoltage trips, anti-islanding settings, and altered fault current (Technical Annex T.3, T.8).
POI: Point of Interconnection — where a load or generator connects to the grid.
PCM: Production Cost Model — a chronological unit-commitment and economic-dispatch simulation of the whole market, used to study congestion, cost, and dispatch (Technical Annex T.10).
PUE: Power Usage Effectiveness — total facility energy divided by IT energy; a data-center efficiency metric (lower is better; best-in-class ≈ 1.3) used as a gate in some jurisdictions (International Experience).
PRC-024 / PRC-029: NERC standards requiring generators (024) and inverter-based resources (029) to ride through voltage and frequency excursions — the model for a future load standard.
PUCT / PURA / SB6: Public Utility Commission of Texas; Public Utility Regulatory Act; Senate Bill 6, the 2025 Texas large-load law.
Ride-through: The ability of a device to remain connected and operating through a grid disturbance rather than tripping offline (Section 4).
RMS / positive-sequence simulation: Phasor-domain modelling at fundamental frequency, assuming a balanced system and representing the network by its impedance; the standard transient-stability tool, and an approximation that breaks down at inverter-dominated interfaces where EMT becomes necessary (Technical Annex T.4).
STATCOM / SVC: Static synchronous compensator / static VAR compensator — fast voltage-support devices at the POI.
UPS / DVFS: Uninterruptible Power Supply; Dynamic Voltage and Frequency Scaling — facility-side systems relevant to ride-through and flexibility.
WLPUN / PCLR: ERCOT's Wholesale Load Point Un-Netted designation and Pre-Commercial Load Resource election, formalizing co-located and pre-energization arrangements.