EngineerHub.orgHow to use this learning simulator
Start with the corridor map and select a transmission technology. Change power, voltage and distance to see current and losses. Then use the transformer and substation modules to follow electricity through voltage conversion and switching equipment.
01 // RouteChoose land, underground or submarine transmission.
02 // TransferCompare current, resistive loss and AC cable charging.
03 // TransformChange voltage and examine transformer loading and efficiency.
04 // SwitchCompare substation busbars under faults and maintenance.
01 // Interactive transmission corridor & loss calculator
The stylised map represents a generating region, a selected transmission corridor and a distant load centre. It is not a real geographic network, and the background terrain does not imply that every selectable technology is suitable for that route. Select the corridor or a technology card to update the route and calculation assumptions.
Voltage pathVoltage is raised for bulk transfer and reduced again near customers. The selected corridor voltage updates with the technology preset.
Generator21 kV ACGeneration voltage
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Step-up transformer400 kV ACLower current for transfer
→
VSC-HVDC corridor±320 kV DCSelected bulk corridor
→
Receiving grid400 / 132 kV ACGrid transformation
→
Regional load132 kV ACSubtransmission level
Corridor inputs
Technology preset
For HVAC, this is active power entering the line. For HVDC, it is AC-bus power available before sending-converter and station-auxiliary losses.
Use effective operating resistance for one AC phase conductor or one DC pole. For bundled conductors, enter the equivalent phase or pole value.
Parallel paths are assumed identical and equally loaded.
An entered active-power screening limit—not a calculated thermal, voltage-stability or transient-stability rating.
Used only for annual energy-loss estimation. Resistive loss scales approximately with current squared.
Annual assumption: The link is treated as energized for 8,760 hours. For HVDC, entered station auxiliary demand is treated as continuous; for HVAC, terminal and compensation-equipment losses are not included.
AC assumptions
Power factor is active power divided by apparent power. For the same MW, lower power factor increases current. Cable charging is calculated from the entered phase-to-ground capacitance.
Converter assumptions
The DC model assumes a balanced symmetrical bipole with equal pole resistance. Monopole, metallic-return and earth-return operation are not modelled.
Resistance, capacitance, thermal rating and converter losses vary with conductor, cable design, temperature, installation and manufacturer. Presets are illustrative rather than catalogue data.
Corridor result
Transfer within selected ratingThe illustrative link remains below its entered power rating.
Transfer current
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Per pole or phase
Delivered power
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After modelled losses
Conductor loss
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Resistive I²R estimate
Terminal / converter loss
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AC terminals not modelled
Modelled efficiency
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Delivered / sent power
Capacity loading
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Power / entered rating
AC cable charging
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Reactive power and current
Annual energy loss
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Using entered annual average transfer
Teaching point: High voltage reduces current for the same transferred power, which strongly reduces resistive loss.
What actually limits a transmission corridor?
The calculator compares power with an entered MW rating, but a real operating limit is the lowest acceptable limit from several different studies—not simply the conductor's nominal current capacity.
Static versus dynamic line rating: overhead-line thermal capacity changes with wind, ambient temperature and solar heating. Dynamic line rating can estimate weather-dependent capacity, but it does not remove voltage, stability or contingency limits.
Guided experimentsLoad two related cases and compare current, conductor loss, charging current and terminal loss.
Start with 220 kV, note the current and loss, then load the 400 kV case. Next compare the long HVAC cable with HVDC on the same route.
02 // Transmission-line and cable explorer
No single technology is best in every location. Route length, power, land access, water crossings, planning constraints, repair strategy, system strength and converter or compensation requirements all matter.
Overhead conductor
Air provides insulation. Conductors are exposed to weather and require wide electrical clearances and rights-of-way.
Extruded underground cable
Compact and visually unobtrusive, but thermal environment, joints, repair access and AC capacitance are important.
Submarine cable
Armouring and marine installation protect the cable. Route survey, burial, crossing design and repair logistics dominate.
Gas-insulated line
Enclosed high-voltage conductor systems can provide compact connections in tunnels or constrained substation areas.
| Technology | Typical strength | Main limitation | Intermediate taps | Power-flow control | Visual footprint |
|---|---|---|---|---|---|
| HVAC overhead | Meshed network integration | Right-of-way and visual impact | Relatively straightforward | Follows AC network physics | High |
| HVAC cable | Dense or sensitive routes | Charging current and thermal repair | Possible but costly | Follows AC network physics | Low above ground |
| HVDC cable | Long submarine/underground transfer | Converter cost and complexity | Complex multi-terminal design | Directly controllable | Low route footprint |
| HVDC overhead | Very long bulk transfer | Converter terminals and DC protection | Less common | Directly controllable | High |
03 // Transformer performance lab
Transformers make AC transmission practical by raising generator voltage and connecting different grid levels. The model includes no-load loss, load-dependent loss, output loading, a direct output-voltage adjustment and approximate current on both sides.
Transformer inputs
The voltage adjustment is an educational direct output-voltage change, not a detailed on-load tap-changer model. No-load loss is treated as constant at the entered energized condition, while rated-current load loss scales with loading squared. Magnetizing current, leakage impedance, voltage regulation, harmonics, temperature correction, thermal ageing and parallel operation are not calculated.
Input-side current
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Output-side current
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Active output
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Active input
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Total loss
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Efficiency
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Adjusted output voltage
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Voltage conversion
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At partial load, no-load core loss remains approximately constant while winding loss falls roughly with current squared.
04 // Substation busbar and switching simulator
A substation is not merely a transformer site. It contains busbars, breakers, disconnectors, instrument transformers, surge arresters, protection, control, auxiliary systems and connections to incoming and outgoing circuits.
Important: The single-line diagrams show functional topology, not physical equipment layout. Circuit availability also depends on actual switch positions, protection zones, breaker-failure logic, remote-end tripping, transformer ratings and operating procedures. Disconnecting sequences, earthing switches and interlocks are intentionally simplified.
05 // HVAC versus HVDC
Most transmission networks are AC because transformers, protection and intermediate network connections are mature and widely deployed. HVDC is added where controlled point-to-point transfer or long cable distance offers a system benefit.
Alternating current
Voltage and current reverse direction periodically. Multiple AC generators remain synchronized within a synchronous area.
Direct current
Polarity remains fixed. Power-electronic converters control transfer and connect the DC link to one or more AC systems.
| Question | HVAC | HVDC |
|---|---|---|
| How is voltage changed? | Conventional power transformers | Power-electronic converter stations plus AC transformers |
| How does power flow? | Determined by network impedance and angle differences | Converter controls schedule the link transfer within limits |
| Long cable behaviour | Charging current and reactive compensation become important | No periodic AC charging current in normal DC operation |
| Connect asynchronous grids? | Not directly | Yes, through the DC link |
| Intermediate network connections | Routine in meshed grids | Possible but multi-terminal systems are more complex |
| Terminal cost and loss | Generally lower terminal complexity | Significant converter investment and converter losses |
| Fault interruption | Mature AC breakers and protection | DC fault interruption and multi-terminal protection are more demanding |
06 // Real transmission project examples
These short examples show why different transmission technologies are selected. The simulator calculations are generic and do not reproduce these projects.
Gotland HVDC — technology milestone
The original Gotland link entered service in 1954 and is widely recognised as the first commercial HVDC transmission system.
Original power20 MW
Original voltage100 kV
Route96 km
LessonSubmarine DC
NorNed — long submarine interconnector
NorNed connects Norway and the Netherlands through a long HVDC submarine cable and supports controllable cross-border exchange.
Capacity700 MW
Length580 km
TypeHVDC cable
In service2008
North Sea Link — large interconnector
The Great Britain–Norway link illustrates modern high-capacity, long-distance submarine interconnection.
Capacity1.4 GW
Routeabout 720 km
TypeHVDC subsea
RoleGrid exchange
07 // Transmission engineering background
Open the topics below for the main physical and operational ideas represented by the simulator.
Lines, voltage and power
For a balanced three-phase AC line, active power is approximately:
P = √3 · VLL · I · PFFor a given power and power factor, a higher voltage produces a lower current. Resistive heating is approximately:
Ploss = 3 I² RBecause current is squared, lowering current has a strong effect on loss.
MW is active power transferred into useful work or heat. MVAr is reactive power associated with electric and magnetic fields and voltage support. MVA is apparent power—the combined magnitude that drives equipment current and rating.
S² = P² + Q² and PF = P / SFor the same MW, lower power factor means higher MVA and therefore higher current.
In a meshed AC network, active power divides among parallel paths according to network impedance and voltage-angle differences. Opening one line changes the impedance network, so power redistributes automatically to remaining paths.
P12 ≈ (V₁V₂ / X) sin(δ₁ − δ₂)This simplified lossless relation explains why lower reactance and larger angle difference increase active-power transfer. It is not a load-flow solution and should not be used near stability limits.
Cable conductors are close to their grounded metallic screens, producing much higher capacitance than an overhead line. AC voltage continually charges and discharges this capacitance, creating charging current and reactive power even when useful load power is low.
Qc ≈ 3 · 2πf · C · Vphase²Compensation, thermal current and voltage control therefore become important as AC cable length increases. The calculator reports charging MVAr and its equivalent current separately; it does not solve the distributed voltage and reactive-power profile or add charging current to the displayed I²R loss.
- Conductor temperature and sag for overhead lines.
- Cable conductor and insulation temperature.
- Voltage stability, transient stability and angle limits.
- Reactive-power capability and voltage control.
- Protection, short-circuit level and equipment ratings.
- Post-contingency security rather than normal-state loading alone.
Shunt reactors absorb reactive power from long AC cables and lightly loaded lines. Capacitor banks, generators, synchronous condensers, SVCs and STATCOMs can supply or absorb reactive power to regulate voltage. Series compensation changes effective line reactance and can increase transfer capability, but protection and stability interactions require detailed study.
The corridor calculator does not size compensation equipment or calculate the distributed receiving-end voltage profile.
Transformers and substations
Alternating current in the primary winding establishes alternating magnetic flux in the core. That changing flux induces voltage in the secondary winding.
V₁ / V₂ ≈ N₁ / N₂Power transformers also have leakage impedance, core loss, winding loss, thermal limits, insulation requirements and tap-changing arrangements.
A busbar is a high-current electrical node connecting line bays, transformer bays, reactors, capacitor banks and other equipment. Busbar arrangement determines how flexibly circuits can be maintained or isolated after a fault.
A circuit breaker is designed to interrupt normal and fault current within its rating. A disconnector creates a visible or assured isolation gap but is generally not used to interrupt significant load or fault current. Operating sequences and interlocks are safety-critical.
AIS: air-insulated switchgear uses open-air clearances, is visually accessible and generally occupies more land.
GIS: gas-insulated switchgear places conductors and switching equipment in compact grounded enclosures. It reduces footprint but increases specialised equipment, interfaces and repair considerations.
Protection systems identify faults and trip the correct breakers. Main and backup schemes, duplicated measurement and trip paths, breaker-failure protection, communication and DC auxiliary supplies are used so one failure does not defeat fault clearance.
Sources and further reading
The simulator uses simplified equations and qualitative equipment descriptions. The following official and primary sources provide context for real transmission planning, transformer resilience, cables, HVDC operation and substation protection.
U.S. Department of Energy — Electric Transmission & Distribution and Protective Measures
U.S. Department of Energy — Large Power Transformer Resilience
U.S. Department of Energy — Transformer and transmission-loss analysis
ENTSO-E — HVDC Links in System Operations
National Grid — High Voltage Direct Current technical information
ENTSO-E — Busbar Differential Protection Report
IEC TC 115 — High-voltage direct-current transmission
IEC 62067:2022 — Extruded-insulation power cable systems above 150 kV
ENTSO-E Technopedia — transmission technology factsheets
U.S. Department of Energy — Dynamic Line Rating report
NERC TPL-001-5.1 — Transmission System Planning Performance Requirements
ENTSO-E Technopedia — STATCOM voltage support
Related EngineerHub electrical tools
Continue from transmission principles into system operation, voltage drop, transformer ratios and circuit calculations.
Frequently asked questions
Higher voltage reduces current for the same transferred power. Lower current reduces conductor heating and allows a given conductor system to move more power, subject to insulation, stability and equipment limits.
No. HVDC can reduce line or cable constraints over suitable routes, but converter stations introduce cost and loss. The outcome depends on distance, power, route type, system needs, converter technology and required network connections.
Underground cables reduce visible line infrastructure, but cable systems have different thermal behaviour, installation cost, jointing, repair, reactive-power and route-access requirements. The best option depends on the project.
Large power transformers are normally highly efficient, but their no-load core loss continues whenever energized and winding loss rises approximately with current squared. Lifetime energy loss remains economically important. The transformer module treats no-load loss as constant and rated-current load loss as approximately proportional to load squared.
More breakers and busbars can improve continuity and maintenance flexibility, but there is no universal best arrangement. Voltage level, circuit importance, fault level, available space, protection philosophy, cost and acceptable outage risk determine the choice.
Only as an initial screening check. Real studies require conductor or cable data, temperature, bundling, skin and proximity effects, sheath and armour losses, reactive current, converter performance, auxiliary demand, operating profile and system studies.