Transmission · HV, EHV and UHV networks
Connecting power generation to the world.
Transmission is the backbone of the electricity system. BARREL covers it end to end — from 11 kV sub-transmission to 765 kV EHV and global UHV AC and HVDC: lines, cables, towers, conductors, substations, equipment, protection, engineering, manufacturing, EPC and maintenance.
- kV covered
- 11–765
- kV UHVDC
- ±800
- Technology areas
- 8
Technology explorer
Lines, cables, HVDC and substations — in depth.
Transmission · 01
Overhead Lines
Bulk power over long distances on towers and poles.
Single, double and multi-circuit lines with bundled conductors, lattice towers, monopoles and complete line hardware — from 11 kV to 765 kV and 1,000 / 1,100 kV UHV AC.
By voltage
- 11, 22, 33 kV
- 66 kV
- 110/115 kV
- 132/138 kV
- 154/161 kV
- 220/230 kV
- 275 kV
- 330/345 kV
- 380/400 kV
- 500/525 kV
- 735/750 kV
- 765 kV
- 1,000/1,100 kV UHV
By circuit
- Single, double, triple, quadruple circuit
- Multi-voltage towers
- Compact lines
- Shared corridors
- Reconductoring and uprating
By tower
- Lattice steel
- Monopole and tubular pole
- H-frame and portal
- Guyed and self-supporting
- Suspension, tension, dead-end
- Transposition
- River, rail and highway crossing
- Long-span and terminal
By terrain
- Plain and agricultural
- Forest
- Hilly and mountainous
- Desert and coastal
- Wetland and river crossing
- Urban corridors
- Snow, ice, seismic, landslide zones
Conductors
- ACSR, AAAC, AAC, ACAR, AACSR
- ACSS
- ACCC and ACCR
- HTLS
- Carbon-core and gap-type
- Thermal-resistant aluminium
- Twin to eight-bundle and UHV bundles
Insulation & accessories
- Porcelain, toughened glass, composite
- Long-rod, suspension and tension strings
- Earthwire, OPGW, ADSS
- Spacer and Stockbridge dampers
- Corona and grading rings
- Clamps, joints, repair sleeves
- Bird diverters, anti-climb, aviation markers
Transmission · 02
Underground Cables
Transmission where overhead lines cannot go.
HV and EHV cables in cities, industrial areas and constrained corridors — direct-buried, in ducts or in tunnels, with thermal management and condition monitoring.
Voltage families
- 11–33 kV
- 66–132 kV
- 145–220 kV
- 245–400 kV
- 500–525 kV
- HVDC cables
Construction
- XLPE and EPR
- Oil-filled
- Mass-impregnated
- Pipe-type
- Single- and three-core
- Copper and aluminium conductors
- Cross-bonded systems
Accessories
- Straight-through and transition joints
- Outdoor, GIS and transformer terminations
- Link boxes and sheath voltage limiters
- Earthing and bonding
- Cable cleats
Infrastructure & monitoring
- Ducts, trenches, tunnels
- Fire barriers
- Distributed temperature sensing
- Partial discharge monitoring
Transmission · 03
Submarine Transmission
Power across the sea.
Subsea AC and HVDC links connect offshore wind, islands and neighbouring grids — with specialist marine partners for laying, burial and protection.
Systems
- Offshore wind export cables
- Inter-array cables
- AC and HVDC export
- Subsea interconnectors
- Island connections
- Floating wind cable systems
Infrastructure
- Cable protection
- Burial and trenching
- Landfall and transition joints
- Offshore converter platforms
- Offshore GIS substations
Transmission · 04
HVDC Transmission
Long-distance, controllable DC power — a technology family of its own.
HVDC is not just a DC line: converter stations, valves and controls are its heart. DC voltage is stated pole-to-ground or pole-to-pole, and BARREL records which.
DC voltages
- ±100 to ±250 kV
- ±320 kV VSC cables
- ±350 to ±450 kV
- ±500 kV
- ±525 kV VSC
- ±600 to ±660 kV
- ±800 kV UHVDC
- ±1,000 / ±1,100 kV
Configurations
- Monopolar — earth or metallic return
- Bipolar — ground or metallic return
- Symmetrical monopole
- Back-to-back
- Point-to-point and multi-terminal
- Overhead, underground, submarine
Converters
- LCC — line commutated
- VSC — two- and three-level
- MMC — modular multilevel
- Hybrid LCC/VSC
- Multi-terminal and back-to-back
Converter station
- Converter transformers
- Thyristor and IGBT valves
- Valve cooling
- Smoothing reactors
- AC and DC harmonic filters
- DC switchyard and breakers
- Electrode lines
- Control and protection
FACTS & advanced
- STATCOM, SVC, TCSC, UPFC
- Series and shunt compensation
- Phase-shifting transformers
- Dynamic line rating
- Grid-forming power electronics
- Wide-area monitoring
Transmission · 05
EHV Substations
The switching, transformation and control centres of the grid.
Substations transform voltage, switch circuits, control power flow, isolate faults and compensate reactive power — from 11 kV to 765 kV and UHV.
Construction
- AIS — air insulated
- GIS — gas insulated
- Hybrid AIS/GIS
- Indoor
- Mobile and containerised
- Digital (process bus, merging units, IEDs)
Function
- Step-up and step-down
- Switching
- Grid and interconnecting
- Renewable pooling and evacuation
- Power plant switchyard
- Industrial and data centre
- Traction and metro
- HVDC converter and back-to-back
- STATCOM / SVC
Busbar schemes
- Single bus, sectionalised
- Main and transfer
- Double bus, double breaker
- One-and-a-half breaker
- Ring and mesh
- H-configuration
- GIS and hybrid arrangements
Engineering
- SLD and general arrangement
- Short-circuit and load flow
- Insulation coordination
- Earthing grid, step and touch
- CT/VT, breaker, transformer sizing
- Relay settings
- Arc flash and harmonics
Civil & fire
- Grading and drainage
- Transformer and gantry foundations
- Control and GIS buildings
- Cable trenches and tunnels
- Oil soak pits and fire walls
- Water spray, foam, gas suppression
Busbar arrangement is chosen for reliability, maintainability, fault level, flexibility, expansion and cost — not by voltage alone.
Transmission · 06
Equipment & Grid Systems
Primary equipment from the transformer to the last clamp.
One manufacturer may make 400 kV and 765 kV transformers, 220 kV breakers and 400 kV GIS — so BARREL records each business once and links it to every product and voltage.
Transformers & reactors
- Power, generator, auto and interconnecting
- Phase-shifting and converter
- Earthing and station service
- Shunt, series, bus and neutral reactors
- Capacitor banks and series compensation
Circuit breakers
- SF₆ and vacuum
- Air-blast, minimum- and bulk-oil
- Dead-tank and live-tank
- Generator breakers
- GIS and hybrid
- HVDC DC breakers
- High-speed grounding switches
Instrument transformers
- CT, VT, PT, CVT
- Combined CT/PT
- Optical and electronic
- Non-conventional and digital sensors
- Bushing and neutral CTs
Insulation & protection
- Surge arresters
- Post, support and bushing insulators
- SF₆ and alternative-gas enclosures
- GIS spacers and bus ducts
- Cable sealing ends
- Grading rings
Busbars
- Aluminium tubular and stranded
- Copper busbars
- Flexible and expansion connectors
- Isolated and non-segregated phase bus ducts
- GIS busbars
- Terminal connectors and clamps
Auxiliary systems
- AC auxiliary supply
- DC battery banks and chargers
- UPS and emergency generators
- Fire detection and oil containment
- HVAC and lighting
- Fibre networks and cybersecurity
- CCTV and access control
Transmission · 07
Protection & Automation
The intelligence that keeps the grid safe and visible.
Protection, control and communication designed together — station bus and process bus, teleprotection, time synchronisation and cybersecurity.
Protection
- Distance and line differential
- Transformer differential
- Busbar protection
- Breaker failure
- Overcurrent and earth fault
- Line and transformer panels
Automation
- Bay control units
- Substation automation systems
- SCADA, RTU, PLC
- IEDs
- IEC 61850 station and process bus
- Merging units
Measurement & records
- GPS time synchronisation
- Phasor measurement units
- Disturbance and event recorders
- Fault locators
- Revenue metering
- Energy management systems
Communication
- Fibre-optic networks
- Teleprotection
- Remote control centre integration
- Redundancy and failover
- Cybersecurity
Transmission · 08
Line Engineering & Design
Line design is an engineering discipline in its own right.
From load flow and route alignment to sag-tension and foundations — and the digital tools that model, survey and monitor the corridor.
System planning
- Load flow and evacuation studies
- Short-circuit
- Transient and voltage stability
- Reactive compensation
- N-1 and N-2 contingency
- Corridor, RoW and route alignment
- GIS mapping, ESIA, clearances
Electrical design
- Voltage and conductor selection
- Thermal rating and bundling
- Corona, RI and audible noise
- EMF studies
- Insulation coordination
- Lightning and switching surges
- Impedance, SIL and transposition
Mechanical & structural
- Tower spotting
- Sag-tension and creep
- Wind, ice, temperature, seismic loads
- Tower analysis
- Crossing design
- Erection and stringing methods
- Clearances and corridor width
Civil
- Open, pile, raft, rock foundations
- Micropiles and anchors
- Access roads and drainage
- Cable trenches and tunnels
- Soil stabilisation and erosion protection
Digital engineering
- PLS-CADD, PLS-TOWER, PLS-POLE
- LiDAR and drone surveys
- 3D terrain models
- Digital twins
- AI defect detection
- Satellite inspection
- Predictive analytics
Global voltage master
Nominal network voltage is not equipment voltage.
A 400 kV network uses 420 kV-class equipment. Dashed tiles are maximum equipment classes (IEC 60038); the rest are nominal voltages. What counts as transmission differs by country — verify against the grid code.
11 kV
MV / sub-transmissionDistribution and industrial networks
13.2–13.8 kV
MVRegional distribution, industrial and generation
15–22 kV
MVRegional, railway, distribution
25 kV
MVRailway traction
30–34.5 kV
MV / sub-transmissionDistribution, renewable evacuation
45–60 kV
HVRegional and industrial systems
66 / 69 kV
HVSub-transmission
72.5 kV
Equipment classFor 66/69 kV systems
88–100 kV
HVRegional systems
110 / 115 kV
HVTransmission and sub-transmission
123 kV
Equipment classFor 110/115 kV systems
132 / 138 kV
HVTransmission
145 kV
Equipment classFor 132/138 kV systems
150–161 kV
HVRegional and North American transmission
187–200 kV
HVJapan, special applications
220 / 230 kV
HV / EHVMajor transmission
245 kV
Equipment classFor 220/230 kV systems
275 kV
EHVUK, Japan and others
300–345 kV
EHVRegional, China, Russia, North America
362 kV
Equipment classFor 345 kV systems
380 / 400 kV
EHVEurope, India and many grids
420 kV
Equipment classFor 400 kV systems
500 / 525 kV
EHVMajor global bulk transmission
550 kV
Equipment classFor 500/525 kV systems
600–700 kV
EHV / specialSpecial high-capacity systems
735 / 750 kV
EHVCanada, China, Russia
765 kV
EHVIndia, North America and others
800 kV
Equipment classFor 765 kV systems
1,000 / 1,100 kV
UHV ACChina and advanced UHV
1,200 kV
UHV researchDevelopment and experimental
Country examples
Representative, not exhaustive national inventories.
- India
- 66, 110, 132, 220, 400, 765 kV; 1,200 kV experimental
- USA
- 69, 115, 138, 161, 230, 345, 500, 765 kV
- Canada
- 69, 115, 138, 230, 315, 500, 735 kV
- China
- 110, 220, 330, 500, 750, 1,000 kV
- Japan
- 66, 77, 110, 132, 154, 187, 220, 275, 500 kV
- UK
- 132, 275, 400 kV
- Germany
- 110, 220, 380 kV
- France
- 63, 90, 225, 400 kV
- Russia
- 110, 220, 330, 500, 750 kV
- Brazil
- 69, 138, 230, 345, 440, 500, 750 kV
- South Africa
- 66, 132, 275, 400, 765 kV
- Australia
- 66, 110, 132, 220, 275, 330, 500 kV
- Gulf
- 110, 132, 220, 230, 380, 400 kV
- South Korea
- 154, 345, 765 kV
Read the numbers right
Voltage is not capacity.
A 400 kV line has no single MW rating. Transfer capability depends on conductor and bundle, circuits, thermal rating, stability limits, reactive power, length, ambient conditions and the network. Likewise, a 765/400 kV substation is a voltage ratio — its MVA depends on the transformers actually installed.
Three-phase power
S = √3 × VLL × I
P = √3 × VLL × I × PF
These give the power for a given voltage, current and power factor — not the safe or stable transfer capacity of a real line.
Technology comparison
Which transmission technology does what.
| Technology | Main purpose | Typical application |
|---|---|---|
| Overhead AC line | Bulk power transfer | Regional and national grids |
| Underground AC cable | Constrained corridors | Cities, industrial areas |
| Submarine AC cable | Short-to-medium subsea links | Offshore wind, islands |
| HVDC overhead line | Long-distance bulk transfer | Inter-regional transfer |
| HVDC cable | DC transfer, underground or subsea | Interconnectors, offshore wind |
| AIS substation | Switching and transformation | Open-land sites |
| GIS substation | Compact switching | Urban and constrained sites |
| Hybrid substation | Mixed AIS/GIS | Space and cost optimisation |
| Digital substation | Digital control and protection | New and upgraded stations |
| HVDC converter station | AC/DC conversion | HVDC terminals |
| STATCOM / SVC | Dynamic reactive support | Voltage and stability control |
For browsing — not a substitute for project-specific design.
Manufacturing ecosystem
Every product family, its own supply chain.
Transmission lines
- Conductors
- ACSR, AAAC, AAC, ACAR, HTLS, ACCC, ACCR
- Aluminium processing
- Rod, wire, alloy, stranded conductor
- Steel processing
- Galvanised wire, structural steel, tower sections
- Towers
- Lattice towers, monopoles, tubular poles, gantries
- Insulators
- Porcelain, glass, polymer, composite
- Line hardware
- Clamps, connectors, dampers, spacers, fittings
- Fibre optics
- OPGW, ADSS, optical fibre
- Cables & accessories
- HV, EHV, XLPE, submarine, HVDC; joints and terminations
- Foundation & earthing
- Concrete, rebar, anchor bolts; earth rods, counterpoise
- Monitoring & survey
- Sag monitors, fault indicators, LiDAR, drones
EHV substations
- Transformers & reactors
- Power and autotransformers; shunt, series, neutral reactors
- Circuit breakers
- SF₆, vacuum, alternative-gas, HVDC DC
- GIS & AIS
- GIS bays and bus ducts; isolators, disconnectors, earth switches
- Instrument transformers
- CT, PT, CVT, optical CT/VT
- Arresters & insulators
- Surge arresters, grading rings, post insulators
- Busbars & capacitors
- Tubular and flexible busbars; shunt, series, coupling capacitors
- Protection & automation
- Relays, IEDs, bay controllers, RTU, SAS, SCADA
- Panels & structures
- Relay and control panels, marshalling kiosks, gantries
- Batteries & fire
- Station batteries, chargers, UPS; detection, suppression, oil containment
- Test equipment
- HV test sets, relay test kits, diagnostics
Conductors
- Electrical-grade aluminium and alloys
- Copper
- Steel and zinc
- Carbon fibre and composite cores
Structures
- Carbon, high-tensile and galvanised steel
- Weathering and stainless steel
- Rebar, cement, aggregates
- Corrosion coatings
Insulation
- Porcelain and toughened glass
- Silicone rubber and EPDM
- XLPE and EPR
- Epoxy and fibreglass
- Pressboard and insulation paper
- Mineral and ester oils
Gases & chemicals
- SF₆ and alternative gas mixtures
- Nitrogen
- Transformer and ester fluids
- Silica gel and desiccants
- Jointing compounds
- Fire suppression agents
BARREL manufactures through OEM partners — T&D equipment.
Testing & commissioning
Proven before it is energised.
- Power transformer
- Ratio, winding resistance, vector group, insulation, tan delta, SFRA, oil
- Circuit breaker
- Timing, contact resistance, travel, insulation, operation
- CT
- Ratio, polarity, excitation, burden, insulation
- VT / CVT
- Ratio, polarity, accuracy, insulation
- Surge arrester
- Leakage current, reference voltage, condition
- Isolator
- Contact resistance, mechanical operation, alignment
- GIS
- Gas quality, leakage, partial discharge, contact resistance
- Cable
- Withstand, VLF, tan delta, partial discharge, sheath
- Battery
- Capacity, discharge, impedance, charger
- Protection relay
- Secondary injection, trip circuits, logic, end-to-end
- Earthing
- Earth resistance, continuity, step and touch
- Line
- Sag-tension, clearances, tower earthing, OPGW OTDR, phasing, thermography
Commissioning sequence
- 01Pre-commissioning inspection
- 02Mechanical and electrical completion
- 03Interlocking and protection verification
- 04SCADA, communication and metering checks
- 05Transformer and busbar energisation
- 06Line charging
- 07Grid synchronisation and load transfer
- 08Reliability run and handover
O&M covers patrols, thermography and drone inspection, vegetation and RoW, oil testing, breaker and GIS maintenance, relay testing, condition monitoring — and modernisation: AIS-to-GIS, digital substations, reconductoring and dynamic line rating.
Project value chain
Twelve stages, from grid plan to recovered metal.
- 01
Grid planning
Load forecast, power flow, evacuation, network plan
- 02
Feasibility & route
Corridor, land, environmental and social
- 03
Detailed engineering
Electrical, structural, civil, protection, communication
- 04
Approvals
Land, forest, environment, aviation, rail, road
- 05
Tender & procurement
Specifications, BOQ, vendor qualification
- 06
Manufacturing & QC
Towers, conductors, transformers, GIS, relays
- 07
Civil construction
Foundations, roads, buildings, trenches
- 08
Erection & installation
Towers, stringing, equipment, busbars, cables
- 09
Testing & commissioning
FAT, SAT, protection, automation, energisation
- 10
Operation & maintenance
Inspection, fault response, asset management
- 11
Modernisation
Uprating, augmentation, digital upgrades
- 12
Decommissioning
Metal recovery, oil treatment, restoration
Delivery and commercial models
- EPC
- Turnkey
- Design and build
- Supply and installation
- BOOT
- BOT
- PPP
- Framework and rate contracts
- Owner's engineer
- PMC
- Independent engineer
- O&M and asset management contracts
Separate BOQ for every package
- 1 Line supply
- 2 Line erection
- 3 Tower foundations and civil
- 4 Stringing and accessories
- 5 Underground cable supply
- 6 Cable laying and jointing
- 7 Substation primary equipment
- 8 Substation secondary equipment
- 9 Control, protection and automation
- 10 Civil and structural
- 11 Fire protection and auxiliaries
- 12 Testing and commissioning
- 13 Operation and maintenance
Standards library
Built to recognised standards.
- IEC 60038 · Standard voltages
- IEC 60071 · Insulation coordination
- IEC 60076 · Power transformers
- IEC 62271 · HV switchgear and controlgear
- IEC 61850 · Utility automation communication
- IEC 60255 · Measuring relays and protection
- IEC 60840 / 62067 · Extruded HV / EHV cables
- IEC 60826 · Overhead line design criteria
- IEC 61284 / 60383 · Line fittings / insulators
- IEC 60099 · Surge arresters
- IEC 60270 · Partial discharge
- IEC 61936-1 · Installations above 1 kV AC
- IEC 62305 · Lightning protection
- IEC 60909 · Short-circuit currents
- IEEE 80 · Substation grounding safety
- IEEE 738 · Conductor current-temperature
- IEEE 519 · Harmonic control
- IEEE C37 · Switchgear and breakers
Bodies: IEC · IEEE · CIGRE · CEA India · BIS · ANSI · ASTM · ASME · ISO · EN / CENELEC · NFPA · NEMA · UL · CSA · AS/NZS. Exact editions, amendments and national adoption are recorded per project.
Research & future transmission
What comes next.
- 1,000 / 1,100 kV UHV AC
- ±800 kV and higher UHVDC
- Multi-terminal HVDC grids
- HVDC circuit breakers
- Hybrid AC/DC networks
- Superconducting cables
- HTLS and composite-core conductors
- Dynamic line rating
- Compact narrow-base towers
- EHV cable tunnels
- Floating offshore wind transmission
- Digital substations
- Optical CT / VT sensing
- SF₆-free switchgear
- AI grid monitoring
- Autonomous drone inspection
- Digital twins
- Wide-area monitoring
- Grid-enhancing technologies
- Grid-forming power electronics
Reference sources
The voltage lists and classifications on this page are a starting taxonomy. Before design or procurement, each voltage is validated against the applicable grid code, IEC/IEEE or national standard and the utility's technical specification.
Transmission enquiry
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