Underground Power Distribution System Restoration Using Inverter Based Resources

TL;DR

This work tackles underground PDS restoration in urban settings by integrating inverter‑based resources into a decision framework that mitigates inrush currents, ferroresonance, and load imbalance. It introduces three models—cable energization with inrush, transformer energization with ferroresonance considerations, and phase swapping for load balancing—and embeds them in a multi‑period MINLP optimized over ESS, PV/WT, and topology. A permutation‑based linearization addresses nonlinearity from phase swapping, enabling tractable solutions. Case studies on the IEEE 123‑Node Test Feeder demonstrate safe energization, controlled resonance risk, and improved phase balance, delivering substantial restored load and renewable integration without compromising device integrity.

Abstract

Underground power distribution systems (PDSs) are increasingly deployed in urban areas. The integration of smart devices including smart switchgears, pad-mounted distribution transformers and inverter-based resources (IBRs) enhance system resilience, however simultaneously introducing unique challenges. The challenges include inrush currents caused by trapped charges in underground cables, ferroresonance in distribution transformers during energization, and three-phase load imbalance resulting from single-phase underground laterals. To address these issues, this paper proposes an underground PDS restoration framework using IBRs. Firstly, an underground cable energization model is developed to quantify inrush current by analyzing voltage differences across both switchgear terminals. Secondly, a distribution transformer energization model is proposed to evaluate ferroresonance using Q-factor constraints based on underground cable capacitance and damping resistance. Thirdly, a phase-swapping model is proposed to improve load balancing by dynamically reassigning lateral-phase connections through smart switchgears. The proposed models are further integrated into a mixed-integer nonlinear programming (MINLP) formulation to maximize the total weighted restored load while constraining inrush currents, ferroresonance, and phase imbalance. To address the nonlinearity induced by impedance matrix reordering during phase swapping, a permutation-based linearization technique is proposed. Finally, case studies on an underground PDS established based on IEEE 123-Node Test Feeder validate the effectiveness of the proposed strategy in improving uderground PDS restoration performance.

Figures (8)

• Figure 1: Diagram of underground PDS model description.
• Figure 2: Energizing underground cables considering inrush current.
• Figure 3: An illustration of distribution transformer energization considering ferroresonance.
• Figure 4: An illustration of phase swapping using swtichgears.
• Figure 5: An illustration of the selected underground PDS based on IEEE 123-Node Test Feeder.