A general method for estimating zonal transmission interface limits from nodal network data

TL;DR

This paper introduces a straightforward, reproducible method to estimate interface transfer limits between user-defined zones in power systems using nodal data and DC power flow approximations, aiding capacity planning.

Contribution

It presents a novel linear optimization approach leveraging PTDF matrices to accurately estimate interface transfer limits from nodal transmission data.

Findings

Significant heterogeneity in ITL ratios across different zones.

Flow direction and contingency levels significantly influence ITL estimates.

The method is demonstrated on a large 134-zone, 65,000-bus system.

Abstract

Capacity expansion models for the electric power system often employ zonal (rather than nodal) resolution, necessitating estimates of aggregate power transfer limits across the interfaces between model zones. Interface limits between planning areas are sometimes published, but they are not generalizable to arbitrary zone shapes. There is thus a need for a reproducible method for estimating interface transfer limits (ITLs) between user-defined zones directly from nodal transmission system data. Here, we present a simple method for estimating ITLs using a DC power flow approximation via the power transfer distribution factor (PTDF) matrix. Linear optimization is performed to identify the distribution of power flows that maximizes the total flow on interface-crossing lines, subject to individual line ratings, limits on bus injection/withdrawal, and the relationships among flows, injections, and withdrawals imposed by the PTDF matrix. We demonstrate the application of the method on a 134-zone ~65000-bus system, and we explore the influence of flow direction, contingency level, and zone size on the estimated ITLs. There is significant heterogeneity in the ratio of the ITL to the sum of interface-crossing line ratings, which highlights the importance of accounting for the physical constraints on power flows imposed by Kirchhoff's laws when estimating zonal ITLs.