Transmission

The transmission network connects all modeled ISO sub-regions via zonal interfaces with directional flow limits and wheeling charges. NYISO internal interfaces are modeled at the zonal level.

Zonal transmission network

The base topology is derived from EIA-930 interchange data, which defines which balancing authority sub-regions are physically connected. Transfer limits vary by source:

  • NYISO internal: NYISO Summer 2025 Operating Study seasonal thermal ratings
  • NYISO external: contractual limits per NYISO Technical Bulletin TB-223
  • Inter-ISO: EIA-930 observed interchange as capacity proxy

NYISO internal zonal interfaces

The 11 NYISO zones are connected by constrained interfaces whose limits are sourced from the NYISO Summer 2025 Operating Study. Directional limits reflect seasonal thermal ratings and can differ by flow direction.

Key constrained interfaces include:

  • Central East (Zone E → F) — historically the most congested east-west boundary
  • UPNY-SENY (Zone F → G) — divides upstate from downstate New York
  • Dunwoodie South (Zone I → J) — constrains flows into New York City
  • Zone J–K (NYC to Long Island) — limited submarine cable capacity

NYISO external interconnections

AC ties

Interface From → To Key Lines
PJM West–West AP → Zone A Homer City–Stolle Rd 345kV, Erie East–S.Ripley 230kV
PJM West–Central PN → Zone C Homer City–Watercure 345kV, E.Towanda–Hillside 230kV
PJM East–Hudson Valley RECO → Zone G Branchburg–Ramapo 500kV, Waldwick–S.Mahwah 345kV (x2)
ISO-NE VT/W.Mass 4003 → Zone F Alps–Berkshire 345kV, Rotterdam–Bear Swamp 230kV
ISO-NE NW CT 4006 → Zone G Pleasant Valley–Long Mountain 345kV

DC cables

Cable From → To Capacity
Linden VFT PS (PJM) → Zone J Variable frequency transformer
Neptune JC (PJM) → Zone K 660 MW HVDC submarine cable
Hudson Transmission (HTP) PS (PJM) → Zone J 660 MW HVDC
Cross Sound Cable 4004 (ISO-NE) → Zone K 330 MW HVDC submarine cable
Northport–Norwalk Cable 4004 (ISO-NE) → Zone K 200 MW AC submarine cable

HVDC projects

Two major HVDC projects are modeled as scheduled interconnections:

  • CHPE (Champlain Hudson Power Express) — 1,250 MW from Quebec to Zone J (NYC). Delivers Canadian hydropower directly into the constrained downstate market. Modeled from its expected in-service date.
  • NECEC (New England Clean Energy Connect) — 1,200 MW from Quebec to ISO-NE. Delivers Canadian hydropower into New England.

Ontario (IESO) interconnection

NYISO Zone D has significant physical interconnection with Ontario via the Niagara/St. Lawrence corridor. Historically this provides 1,000–2,000 MW of baseload hydro imports. This interconnection is not currently modeled — Ontario imports are zero, meaning Zone D prices may be biased upward. CHPE (1,250 MW from Quebec to Zone J) partially compensates but enters Zone J directly, not through upstate.

Wheeling charges

Directional wheeling tariffs create “hurdle rates” — the price differential between zones must exceed the tariff before power flows. Two sets of rates are used, applied at different solve stages:

Stage Source Purpose
Unit commitment Gold Book Fig A-2 “Commitment Hurdle Rates” Higher rates — discourages speculative cross-ISO scheduling
Redispatch Gold Book Fig A-3 “Dispatch Hurdle Rates” Lower rates — allows responsive real-time flows

Flows are decomposed into forward and backward components (non-negative). When multiple physical interfaces share a model branch (e.g., Linden VFT and HTP both map to PS–ZONJ), the maximum rate per direction is used. Internal NYISO zonal interfaces carry zero wheeling charges — congestion is captured through the line flow limits.

Input Source Link
Commitment hurdle rates NYISO Gold Book Appendix A, Figure A-2 (2023-2042 Outlook) Gold Book Appendix A
Dispatch hurdle rates NYISO Gold Book Appendix A, Figure A-3 Gold Book Appendix A
Interface definitions NYISO Appendix E NYISO App E

Assumptions and caveats

  • Transmission expansion is exogenous — line capacities are not optimised by the model.
  • Inter-ISO limits outside NYISO use EIA-930 observed interchange as a capacity proxy, which may understate actual transfer capability.
  • Wheeling charges are static across the forecast horizon (no escalation modeled).
  • Ontario (IESO) interconnections are not modeled; Canadian imports via CHPE and NECEC are treated as scheduled HVDC flows.

Data sources

Source Description Link
EIA-930 BA-level interchange flows for topology and line capacities EIA-930
NYISO Summer 2025 Operating Study Internal zonal interface limits NYISO
NYISO TB-223 External scheduled line limits and interconnection definitions TB-223
NYISO Gold Book Appendix A Commitment and dispatch hurdle rates NYISO Gold Book
NYISO Appendix E Interface definitions and line-level detail App E
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