What if underground cables replaced all overhead lines? [12]

Replacing all overhead lines (OHL) with underground cables (UGC) would transform the visual footprint of grids and reduce exposure to wind, ice, and wildfire risks—but at multiples of the cost, with longer repair times, complex construction impacts, and non-trivial thermal/operational constraints. Recent benchmarking shows underground transmission can be ~4.5× (often 4–14×) the cost of equivalent overhead; even distribution undergrounding typically runs ~4–6× the cost of aerial construction. Outage frequency tends to fall with undergrounding, but restoration times rise—as locating and repairing faults underground takes days to weeks versus hours to days for overhead. [theiet.org], [pdi2.org] [pdi2.org], [cdn.xcelen...ission.com]

Globally, the share of underground transmission remains small (U.S. 200 kV+ underground ≈0.5%), while distribution undergrounding has crept up to ~20% by 2023 as cities densify. Select countries are building long HVDC underground corridors (e.g., Germany’s ±525 kV SuedLink/SuedOstLink), demonstrating technical feasibility over hundreds of kilometers—driven by public acceptance, energy transition logistics, and planning mandates. [energy.gov] [nkt.com], [cabletechn...news.co.uk]

Our position: Full undergrounding is neither necessary nor economical. Value-maximizing strategy is targeted undergrounding—urban cores, environmentally sensitive crossings, cyclone/wildfire corridors, and aesthetic hotspots—combined with overhead reinforcement and smart operations. In India, undergrounding can materially improve safety and reliability in dense localities (Delhi pilots) and enhance resilience in cyclone-prone coasts—provided projects are scoped selectively, funded within RDSS modernization envelopes, and built to CEA 2023 safety standards. [hindustantimes.com], [theweek.in], [pib.gov.in], [cea.nic.in]

Global energy & grid context: why the question matters

Electricity demand is rising faster than overall energy demand, while climate-related extreme weather drives outage spikes—hence the appeal of burying lines. U.S. analysis links ~83% of major outages (2000–2021) to weather, with a ~78% increase in weather-related outages in 2011–2021 vs. 2000–2011, focusing resilience debates on hardening versus selective undergrounding. Yet, despite benefits, transmission undergrounding is rare (≈0.5% of 200 kV+ route-miles) due to cost, construction complexity, and operations constraints. [powermag.com] [energy.gov]

By contrast, distribution undergrounding has expanded (U.S. ~20% underground by 2023), mostly in new urban developments or targeted conversions—illustrating that undergrounding scales more readily at lower voltages and shorter distances. [energy.gov]

Technical & economic realities: overhead vs underground

1) Cost multiples

Independent UK analysis (IET/Mott MacDonald, 2025): underground cable solutions average ~4.5× OHL lifetime cost per MW-km; offshore HVDC can be up to 11×. [theiet.org]
U.S. utility/state studies: transmission underground ~4–14× overhead; distribution underground ~4–6× overhead. [pdi2.org]
Utility factsheets echo 8–16× for HV transmission underground, reflecting trenching, vaults, civil works, and specialized accessories. [greatriverenergy.com]

2) Reliability & restoration

Reliability data show lower outage frequency for underground distribution, but ~58% longer restoration times vs overhead—because locating/repairing buried faults is harder. [pdi2.org]
Transmission underground failures are rarer but slower to fix: utilities cite weeks to months to locate and repair serious cable faults vs hours to days for overhead line repairs. [cdn.xcelen...ission.com]

3) Thermal & capacity constraints

Overhead lines dissipate heat to air; underground cables must shed heat to soil/duct banks, often requiring duct banks, thermal backfill, or forced cooling, limiting ampacity and increasing ancillary equipment count (more joints, terminations). [cdn.xcelen...ission.com], [pdi2.org]
CIGRE/IEEE literature emphasizes ampacity management and ratings: accurate thermal models, soil parameters, and accessory reliability are central to UGC operations. [cigre.org], [ieeexplore.ieee.org]

4) Construction impacts & environment

OHL spans sensitive areas with tower footprints; UGC typically requires continuous trenching, splice vaults every ~600–800 m (MV) / 1,500–2,500 ft (HV), road crossings, and directional drillings—producing longer, more disruptive works. [cdn.xcelen...ission.com], [greatriverenergy.com]
DOE/LBNL guidance underscores that trenching, permitting, and utility coordination drive timelines and costs—especially in dense corridors with multiple buried assets (sewer, gas, fiber). [energy.gov]

5) Asset aging & failure patterns

EPRI data indicate underground systems follow a “bathtub curve” (early infant failures → long stable period → late-life aging). Median failure rates reported: ~1.3 cable, 0.4 joints, 0.2 terminations per 100 conductor‑miles per year, with dispersion by vintage, insulation, and workmanship. [distributi...n.epri.com]
Wet/submerged environments stress extruded insulations (e.g., water treeing), necessitating proactive monitoring (Tan δ, PD tests) to sustain reliability. [nrc.gov]

Where undergrounding does make sense (globally)

Urban cores & constrained corridors.
Densely built areas, airports, or view-sensitive landscapes justify undergrounding to meet right‑of‑way constraints and address visual amenity concerns—despite higher capex. Utilities routinely choose UGC where overhead siting is impractical. [cdn.xcelen...ission.com]

Environmental/wildfire resilience zones.
Undergrounding materially reduces ignition risk; PG&E’s strategic program reports near‑elimination (~98%) of wildfire ignition risk on undergrounded sections and cost-per-mile falling to ~$3.1 M by 2025 through learning and scale. [undergroun...ucture.com], [ecmag.com]

Long HVDC corridors with public acceptance mandates.
Germany’s SuedLink/SuedOstLink (±525 kV, 2×2 GW) are land HVDC largely underground—approved after opposition to overhead lines; installation began in 2024–2025, with completion targeted 2026–2028. These projects prove technical feasibility for hundreds of km at 525 kV, using XLPE and stringent after‑installation testing (PD, DC/AC). [cabletechn...news.co.uk], [powerpeakdigest.com], [inmr.com]

India: present scenarios and implications

Extreme weather & cyclone resilience.
India’s east coast is highly vulnerable—13 coastal states/UTs, 84 coastal districts exposed; Bay of Bengal cyclones are frequent and severe. Resilience planning highlights the need for standards and robust equipment able to withstand Category‑4 winds, and for master‑planning critical infrastructure. Undergrounding distribution circuits in salt‑spray, wind, and debris zones can reduce mechanical damage, though marine/groundwater conditions require careful insulation and sealing. [ncrmp.gov.in], [mdpi.com]

Urban reliability & safety.
Delhi has launched pilots to replace overhead LT/HT wiring with underground feeder/service cables (IoT‑monitored feeder pillars, remote fault isolation) in Shalimar Bagh and Janakpuri. This aims to reduce monsoon‑season hazards and outages while improving aesthetics, with ₹100 crore budgeted for broader rollout. [hindustantimes.com], [theweek.in]

Grid modernization under RDSS.
The Revamped Distribution Sector Scheme funds modernisation: smart meters, SCADA/DMS, substation upgrades—and includes underground cabling works where justified. As of mid‑2025, 20.33 crore smart meters sanctioned and 2.27–2.41 crore installed; the Ministry indicates underground cabling is part of approved modernization works, linking investments to AT&C loss reduction and ACS‑ARR performance. [energetica-india.net], [energyasia.co.in]

Safety & standards.
The CEA (Measures relating to Safety and Electric Supply) Regulations, 2023 apply across generation, transmission, distribution, and use—specifying safe installation practices, licensed supervision, and inspection regimes. Any undergrounding must comply with these regulations, which centralize responsibility and testing requirements (with 11 kV as the notified voltage threshold for certain self‑certification in the Central jurisdiction). [cea.nic.in], [pib.gov.in]

If India undergrounded all lines: benefits vs. trade‑offs

Benefits

Weather resilience: Reduced exposure to wind, falling trees, and flying debris; fewer outage events in cyclones/monsoons; lower wildfire ignition risk in dry corridors. [mdpi.com], [ecmag.com]
Safety & aesthetics: Eliminates tangled aerial webs in dense neighborhoods; fewer electrocution risks from snapped conductors; cleaner streetscapes. Delhi pilots explicitly target “wire‑free” neighborhoods. [hindustantimes.com]
Right‑of‑way: Feasible routing through constrained urban corridors; potential reduction in siting disputes for new capacity. [cdn.xcelen...ission.com]

Costs & constraints

Capital burden: Transmission undergrounding at ~4–14× overhead (often higher in challenging terrains) would impose multi‑lakh‑crore capex; distribution undergrounding ~4–6× overhead; lifecycle O&M requires specialized crews. [pdi2.org]
Longer restorations: Fewer faults overall but slower repairs (days–weeks), meaning large blackouts after rare underground failures can persist longer. [cdn.xcelen...ission.com], [pdi2.org]
Thermal limits: Soil thermal resistivity, heating in duct banks, and lack of natural cooling can limit ampacity and necessitate additional circuits and reactive/compensation equipment. [pdi2.org]
Construction disruption: Continuous trenching, vaults, and road‑cutting permissions extend timelines; urban works affect traffic, utilities, and local businesses longer than pole‑setting. [greatriverenergy.com]
Supply chain & skills: XLPE HVDC/HVAC extruded systems, accessories, and experienced jointers are scarce; Germany’s corridors highlight large logistics and testing regimes—replicating at Indian scale would stress capability. [nkt.com], [inmr.com]

Net assessment

At national scale, full undergrounding would not be cost‑optimal versus targeted undergrounding + overhead hardening (stronger poles, covered conductors, vegetation management), dynamic line ratings, and automation. [powermag.com], [ferc.gov]

A pragmatic pathway: selective undergrounding + smart overhead

1) Adopt a tiered siting policy

Tier‑1 (Must underground): Dense urban cores; high‑risk wildfire corridors; critical crossings (rail, airport, heritage); cyclone‑exposed coastal feeders with repeated aerial failures. Use UGC with advanced monitoring (PD, Tan δ) and IoT to minimize restoration times. [nrc.gov], [hindustantimes.com]
Tier‑2 (Hybrid): Transmission spurs near cities and environmentally sensitive segments: short UGC segments with overhead elsewhere; where public acceptance mandates, consider HVDC UGC (Germany‑style) for long corridors—with rigorous cost-benefit scrutiny. [cabletechn...news.co.uk]
Tier‑3 (Overhead optimized): Rural bulk transmission and distribution: reinforce structures, deploy covered conductors and smarter protection; apply DLR/AAR to increase transfer capability under favorable weather. [ferc.gov]

2) Strengthen planning & construction management

Thermal design: Use soil thermal backfills, ampacity modeling (CIGRE/IEEE methods), and accessory reliability programs to avoid derating. [cigre.org], [ieeexplore.ieee.org]
Civil delivery: Plan trench logistics, vault spacing, traffic management, and HDD for watercourses; budget for 3–6× longer build durations than overhead. [cdn.xcelen...ission.com]
Restoration readiness: Invest in fault location and specialized repair crews, spares (joints/terminations), and pre‑authorised permits to compress repair windows. [link.springer.com]

3) Harness RDSS funds smartly

Use RDSS to prioritize undergrounding where it unlocks reliability and safety KPIs (AT&C, SAIDI/SAIFI), alongside smart meters, SCADA/DMS, and substation upgrades; document payback via reduction in repeated monsoon/cyclone failures and feasible theft deterrence in select pockets. [energetica-india.net]

4) Enforce safety & quality (CEA 2023)

Require licensed contractors, competent supervision, testing, and compliance with CEA (Safety & Electric Supply) Regulations, 2023 across all underground works; coordinate with state electrical inspectorates for inspection and notified voltage self‑certification protocols. [cea.nic.in], [pib.gov.in]

Illustrative business case (India)

Use case A: Coastal distribution feeders in Odisha/Tamil Nadu

Problem: Recurrent cyclone damage to poles/wires; prolonged outages; public safety risks.
Intervention: Convert select feeders to underground, with vault spacing and flood‑resilient design; integrate feeder automation for sectionalization.
Expected impact: Fewer weather‑related faults; shorter fault isolation; longer restoration time per fault offset by lower fault frequency; improved SAIDI/SAIFI in peak cyclone months. [mdpi.com]

Use case B: Delhi residential pockets

Problem: Hazardous aerial clusters; theft tapping; monsoon faults.
Intervention: Underground LT networks with feeder pillars, IoT sensors, remote fault isolation (FRTUs).
Expected impact: Safety, aesthetics, lower nuisance outages; measurable reliability uplift; data‑driven maintenance from sensor feeds; funded through city allocations (₹100 crore), phased scaling post pilots. [hindustantimes.com]

Use case C: Long‑haul corridors with acceptance constraints

Problem: Public opposition to new OHL; renewable‑to‑load transfer bottlenecks.
Intervention: Evaluate HVDC UGC segments (±525 kV) only where acceptance and planning dictate, learning from Germany’s execution/testing methods; compare to optimized OHL + compensation.
Expected impact: Deliverability with social license, at higher capex; requires manufacturing/logistics/testing capacity and rigorous cost‑benefit governance. [inmr.com]

Risks & mitigations

Capex escalation → Stage‑gate approvals with levelized cost per reliability point; prioritize feeders with documented recurrent failures or safety incidents. [energy.gov]
Long repair durations → Pre‑position spares; invest in TDR/PD diagnostics; train jointers; pre‑clear permits for emergency digs. [link.springer.com]
Thermal constraints → Robust ampacity modeling per CIGRE/IEEE; select backfills; possibly derate and duplicate circuits to meet peak loads. [cigre.org]
Execution disruption → Traffic and utility coordination; phasing to limit business impacts; HDD for rivers and arterial roads. [greatriverenergy.com]
Supply chain bottlenecks → Framework agreements with cable vendors; accessory testing; workforce development (jointers, civil crews). Germany’s corridor programs highlight scale and logistics needs. [nkt.com]

Bottom line

Undergrounding all lines would yield aesthetic and resilience gains—but at prohibitive cost and with operational trade‑offs. The optimal path is selective undergrounding in high‑value segments, combined with smart overhead reinforcement, automation, and standards‑compliant delivery. Germany’s HVDC corridors show underground can scale where social license demands it; India’s urban pilots show near‑term value in safety and reliability. A portfolio approach—guided by data, standards (CEA 2023), and disciplined economics—will outperform blanket undergrounding.

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