THE GLOBAL EDITION 01

Grid engineering · interactive learning lab

Inside an electrical substation

Follow three phases from an incoming line, through a transformer, to two outgoing feeders. Explore what switches, what measures, what protects—and where energy is lost.

A deliberately small air-insulated substation (AIS): one high-voltage (HV) bus, one transformer, one medium-voltage (MV) bus. The illustrative 110/20 kV values are line-to-line root-mean-square (LL RMS) voltages. Frequency is 50 hertz (Hz): 50 cycles per second.

Original educational visualization—not an approved installation, clearance assessment or switching procedure. Dimensions and component sizes are adjusted for visibility.

Follow the power through the station

Inspect the connected substation in 3D

Orbit the station, select equipment and inspect individual cutaways. The diagram, calculations and explanations remain available without 3D.

Drag to orbit; pinch or scroll to zoom. Focus the model for arrow-key rotation, +/− zoom and Home reset. Equipment and diagram buttons provide keyboard selection.

Gold markers, arrows and elevated dashed routes show schematic net energy flow, not an extra conductor, instantaneous current direction or electron speed. The feeder A route disappears in its open-breaker snapshot; all energy routes disappear when the source is isolated.

A/B/C labels identify the three AC phases. PE identifies protective earth, not a normal load return. Grey dashed leaders are annotation callouts, not electrical connections. Cutaways are enlarged static explanations, not validated electrical simulations or switching instructions.

The breaker detail has a fixed open contact gap to explain interruption; it is not the operating state of the whole-station snapshot.

Measurement samples foreground frame cadence and CPU render submission. It does not measure GPU execution, Core Web Vitals, engineering accuracy or a physical mobile device. No artificial throttling is applied by this tool.

Original single-line diagram: one HV bus, one transformer, two MV feedersOne stroke represents all three phases. Disconnectors and breakers are distinct. CTs are series; VTs and arresters connect in shunt. Grounded-star/star transformer has separate windings with zero degree phase displacement. Measurement and trip controls are not in the main energy path. Select the corresponding equipment buttons above.DS closedCTIncoming bay · 3φHV busCTTransformer bayYNyn110/20 kVYNyn0 · 0°MV incomerMV busCTLoad AFeeder A cableCTLoad BFeeder B cableVT · shuntSA · shunt arresterES open · no load returnCT/VT → relay → DC trip → breakerDS: disconnector · square: breaker · CT: series current transformer · VT: shunt voltage transformer · ES: earthing switch
Single-line shorthand: every main stroke represents A, B and C. Normal-service conceptual state. Protective earth (PE) is separate. This drawing is original, not a wiring or switching instruction. The calculated auxiliary equivalent is a balanced resistance at the MV bus; its service transformer and branch apparatus are omitted from these equipment drawings.

One circuit. One checked power balance.

Change nominal load demand to see consistent RMS currents, voltage drop and losses. Loads are balanced constant impedances, specified by their active power and lagging power factor at 20 kV. A kilowatt (kW) is 1,000 watts; a kilovolt (kV) is 1,000 volts. Actual delivered power is slightly lower after voltage drop; these inputs are not equipment ratings.

Illustrative operating point

Prevalidated snapshots only, not switching sequences. No earthing-switch closing control is provided. The disconnected upstream line may still be live; zero station readings do not establish safe access. In the isolated snapshot the station battery can still power protection, outside this AC ledger.

Calculated measurement points · balanced sinusoidal steady state
Measurement pointVoltage, LL RMS (kV)Line RMS current (A)Active power (kW)
HV station side, downstream of incoming breaker110.00040.7136,994.957
MV bus, after transformer winding resistance19.972223.5306,967.965
Feeder A load terminals19.892127.6103,957.107
Feeder B load terminals19.88395.6602,964.873
HV input
6,994.957 kW
Delivered to A + B
6,921.980 kW
Cable resistive losses
36.013 kW
Transformer winding loss
11.992 kW
Transformer no-load loss
15.000 kW
Station auxiliary consumption
9.972 kW
Load delivery / HV input
98.957%
Power-balance residual
< 0.000001 W

Input = delivered + cable loss + winding loss + no-load loss + auxiliary consumption. Display rounding may alter the last digit; the residual uses unrounded values. Auxiliaries do useful work inside the station and are not delivered to the two loads.

Assumed balanced 50 Hz MV bus phase-to-neutral fundamental voltagesPhase APhase BPhase C±16.31 kV peak · phase–neutral0–40 ms
Two cycles; each phase is displaced by 120°. Time zero is referenced to local MV phase A, not source-synchronized. This plot is the assumed sinusoidal fundamental evaluated from the calculated bus RMS voltage, not measured data or a transient simulation. Alternating current reverses direction; gold 3D markers indicate net energy flow instead.

Equations and assumptions

S = √3 VLL,rms Iline,rms; P = S cos(φ)
S is apparent power (volt-amperes, VA), P is active power (watts, W), V is line-to-line RMS voltage (volts, V), I is line RMS current (amperes, A), φ is the voltage–current phase angle and cos(φ) is power factor. These apply to balanced sinusoidal three-phase quantities, not arbitrary switching waveforms.
Q = P tan(φ); Zload = Vphase,nom² / conj[(P + jQ)/3]
Q is reactive power (var); j² = −1. Z is the per-phase load impedance (ohms, Ω); conj means complex conjugate. Vphase,nom = 20,000/√3 V. P and Q here are the nominal total three-phase load, so changing an input defines a new impedance.
Y = Σ 1/(Rcable + Zload) + Yaux; Vbus = Vsource / (1 + Req Y)
Y is total per-phase admittance (siemens, S). Yaux is the real auxiliary admittance per phase, defined by 10,000 W / (3 × Vphase,nom²). Vbus is the phase-to-neutral RMS bus-voltage phasor, not the line-to-line magnitude in the table. Vsource = 20,000/√3 V is the ideal transformer secondary no-load phase voltage. Req = 0.08 Ω is MV-referred winding resistance per phase. V and I in this circuit equation are RMS complex phasors. Open branches have zero admittance.
Ifeeder = Vbus / (Rcable + Zload); Pcable = 3 |Ifeeder|² Rcable
The factor 3 includes all three phase conductors, each with the stated resistance. No neutral or earth return is included. Receiving phase voltage = Vbus − Ifeeder Rcable. Winding loss similarly uses the phasor sum of feeder and auxiliary currents, not the sum of their magnitudes.
ηdelivery = Ploads / PHV input
η is the model's load-delivery efficiency; it includes station auxiliary consumption in the denominator. It is not a manufacturer's guaranteed transformer efficiency.

All resistances and losses are invented teaching inputs: feeder A 0.4 Ω per phase, feeder B 0.6 Ω per phase, winding 0.08 Ω referred to MV, fixed no-load loss 15 kW at the energized 110 kV source, and station auxiliary impedance equivalent to 10 kW at 20 kV. No magnetizing reactive current, leakage/cable reactance, saturation, harmonics, tap changer action, temperature dependence, fault duty or thermal rating is calculated.

Published example: 4,000 + 3,000 kW nominal, pf 0.90

Normal service: MV bus 19.972 kV; feeder currents 127.610 A and 95.660 A. HV input 6,994.957 kW = 6,921.980 kW delivered + 36.013 kW cable losses + 11.992 kW winding loss + 15.000 kW core loss + 9.972 kW auxiliaries, to rounding precision. Load-delivery efficiency 98.957%. This is an illustrative calculated point, not a real station record.

What each component actually does

Terms and symbols
AIS
Air-insulated switchgear: outdoor live parts use air and insulators to separate them from other phases and grounded structures.
HV / MV
High voltage / medium voltage. Here the invented nominal levels are 110 kV / 20 kV; category boundaries and practices depend on the relevant system and standard.
RMS
Root mean square: the magnitude equivalent to DC for the heating effect in a resistor. For a sinusoid, peak magnitude is √2 times RMS.
P / Q / S
Real power P (W), reactive power Q (var), and apparent-power magnitude S (VA). For sinusoidal quantities, S = √(P² + Q²); reactive power is not an extra energy-loss term.
VLL / Iline
RMS line-to-line voltage / RMS current in one phase conductor. Vphase is voltage from a star phase terminal to its neutral point.
cos(φ)
Sinusoidal displacement power factor: φ is the angle between corresponding phase voltage and current. It is not a general switching-waveform power factor.
CT / VT
Current transformer / voltage transformer, used to supply scaled measurement signals to instruments or relays.
Phasor
A complex number expressing a sinusoid's magnitude and phase angle at one common frequency. Here magnitudes are RMS; a phasor is not a time-domain switching waveform.
N, n / PE
HV and MV star neutral points / protective earth. Distinct labels and connections, even where both ultimately join an earthing system.

1. Incoming three-phase line and HV bay

Three conductors, labelled A, B and C, bring alternating current (AC) into the yard. Insulators support live conductors without connecting them to grounded steelwork. The incoming bay contains a breaker, disconnectors and measurement equipment: these have different jobs, even when they look similar from a distance.

Engineering details

The invented supply is 110 kilovolts (kV) line-to-line root mean square (RMS), at 50 hertz (Hz), or 50 cycles per second. RMS describes the heating-equivalent magnitude; it is not a waveform's peak. Balanced phase voltages are 120° apart. A circuit breaker interrupts its specified current duty; this lesson's ordinary disconnectors provide isolation and are not shown breaking load current. Curved spans are attached through insulator fittings. Their sag and enlarged diameter improve legibility; temperature, weight and tension would require a separate mechanical design. The dedicated HV breaker detail is an enlarged, fixed-open illustration of an SF6 (sulfur hexafluoride) gas interrupter: contacts, insulating nozzle, partial chamber, drive link and trip coil. Gas flow helps cool an arc near an AC current zero; insulation must recover afterwards. No gas flow, contact motion, full puffer/self-blast mechanism, arc or interruption duty is simulated. SF6 is a potent greenhouse gas if released. SF6-free HV designs also exist, but this cutaway does not represent one.

Checked sources: MIT / J. L. Kirtley: Polyphase Networks; Hitachi Energy: Disconnectors; Hitachi Energy: Air-insulated switchgear portfolio; National Grid: Overhead Line Conductor and Fittings; National Grid: hot-weather advice; ABB Review 1/2007: The circuit breaker — SF6 interruption principle; Hitachi Energy: SF6 environmental impact and alternative high-voltage technology. Book reading: [R1], [R4].

2. One high-voltage bus

A busbar is a shared electrical connection. This station has one bus for each of the three high-voltage (HV) phases. Supported metal conductors connect the incoming bay to the transformer bay; the support columns and foundations do not carry the normal load current.

Engineering details

The diagram represents one three-phase bus as a single line, not as one physical wire. Phase A joins A, B joins B and C joins C; different phases are never tied together. A voltage transformer (VT) measures voltage through a shunt connection. Its primary is not a compulsory series route for load power. A single bus is deliberately used: there is no hidden second source, bus coupler or spare transformer. Losing its only supply therefore removes the main supply to both feeders; the model makes no redundancy claim.

Checked sources: ABB: Instrument Transformers — Technical Information and Application Guide; Short: Electric Power Distribution Handbook — authorized book preview; ABB: Distribution Automation Handbook — Elements of power distribution systems. Book reading: [R1], [R5].

3. Transformer bay: interrupt, isolate and measure

The transformer bay links the HV bus to the transformer. A breaker can interrupt current; disconnectors show isolation gaps. Current transformers (CTs) measure the current passing through the phase conductors. Surge arresters form separate protective branches beside the transformer, not another load-power stage.

Engineering details

CT primary conductors are in series with each phase; secondary circuits feed instruments and relays rather than the power-transformer winding. VTs are shunt devices. An open CT secondary can develop hazardous voltage while primary current flows; this viewer is not a wiring exercise. Surge arresters limit overvoltages; selecting them requires coordination with equipment insulation. Earthing switches are shown open in every conceptual snapshot; no closing action is provided. An isolated-state label and zero calculated readings do not establish that equipment is safe to earth or access. Arrester coordination, fault-interruption capability, insulation clearances and protection settings have not been designed here.

Checked sources: ABB: Instrument Transformers — Technical Information and Application Guide; Hitachi Energy: Disconnectors; Hitachi Energy: Air-insulated switchgear portfolio; ABB: Distribution Automation Handbook — Elements of power distribution systems. Book reading: [R1], [R3].

4. Power transformer: 110 kV to 20 kV

The transformer changes AC voltage without changing the grid frequency. Separate windings share a changing magnetic field in a steel core. Electricity does not travel from one winding to the other through the core. Bushings insulate terminals from the tank; oil and radiators carry heat away from the active parts.

Engineering details

The illustrative vector group is YNyn0: HV and lower-voltage windings are star-connected, both neutral points are brought out, and corresponding ideal voltages have 0° displacement. The lower-voltage winding is still medium voltage (MV), not a household low-voltage supply. Both neutral points are grounded in this chosen teaching arrangement, separately from the tank's protective bond. No delta winding or unmodelled tertiary is claimed. VLL is line-to-line RMS voltage and Vphase is phase-to-neutral RMS voltage. For this star/star case, Vphase = VLL/√3 on both sides. Winding-turn counts NH and NM therefore give an ideal ratio NH/NM equal to the no-load line-voltage ratio 110/20 = 5.5. This does not generalize unchanged to a delta/star transformer. The circuit includes MV-referred series winding resistance, so the actual loaded MV bus voltage is slightly below its nominal value. A fixed HV-side shunt represents no-load real loss. Leakage reactance, magnetizing reactive current, tap regulation, inrush and thermal performance are not solved.

Checked sources: ABB: SPAD 346 C stabilized differential relay — YNyn0 application; Gass: transformer vector-group notation; MIT / J. L. Kirtley: Polyphase Networks; MIT / J. L. Kirtley: Magnetic Circuit Analog to Electric Circuits; Hitachi Energy: liquid-filled transformer construction; ABB: Distribution Automation Handbook — Elements of power distribution systems. Book reading: [R2], [R4].

5. MV incomer, switchboard and common bus

The transformer's three MV phases connect to the switchboard incomer. Three separate busbars distribute power to two outgoing feeder panels. Opened enclosures and the separate switchgear cutaway reveal the bus, breaker, measurement and cable compartments. These viewing cuts do not represent equipment left open in normal energized service.

Engineering details

The nominal teaching level is 20 kV line-to-line RMS; its actual bus voltage depends on calculated winding drop. Metal enclosures are protectively bonded; live busbars remain insulated from them. The overview shows CT primaries in series in the outgoing feeders and VT branches on the HV side. The separate MV switchgear detail also shows a CT ring around each series phase path; no MV VT branch or incomer CT is modelled in the overview. Opened MV cabinets are a visibility device, not a claim that exposed live MV equipment is a normal installation. The MV switchgear view shows simplified vacuum-interrupter bottles, not the separate HV gas-breaker detail. In a real vacuum interrupter, separating contacts can form a metal-vapour arc; AC interruption depends on current zero and insulation recovery. This geometry does not expose a validated internal vacuum design or simulate an arc. The main path remains AC throughout this substation; a small station DC supply serves controls, not AC/DC transmission conversion.

Checked sources: Schneider Electric: Functions of the substation with MV metering; ABB Review 1/2004: vacuum interrupters; ABB: Instrument Transformers — Technical Information and Application Guide; ABB: Distribution Automation Handbook — Elements of power distribution systems. Book reading: [R1], [R5].

6. Outgoing feeder A and its load

A feeder is an outgoing circuit. Feeder A has its own breaker and measurement circuit and supplies a separate balanced three-phase load. The feeder's conductors lose some energy as heat, so the power arriving at its load is smaller than the power leaving the MV bus.

Engineering details

The demand control defines a balanced load's nominal real power at 20 kV, not a fixed delivered power. The model turns that nominal power and sinusoidal power factor into a constant per-phase load impedance Z, measured in ohms (Ω); actual demand then varies with the calculated terminal voltage. At each actual measurement point, S = √3 VLL Iline and P = S cos(φ). φ is the local voltage–current angle, S is in volt-amperes (VA), P in watts (W), VLL in RMS volts (V) and Iline in RMS amperes (A). Each feeder conductor has per-phase resistance R: total resistive loss is 3Iline²R. Receiving phase-voltage phasor equals MV-bus phasor minus current phasor times R. This is a balanced sinusoidal steady-state circuit, not transient, harmonic or thermal simulation.

Checked sources: Schneider Electric: Installed apparent power (kVA); MIT / J. L. Kirtley: Polyphase Networks; Short: Electric Power Distribution Handbook — authorized book preview. Book reading: [R4], [R5].

7. Outgoing feeder B and the shared power balance

Feeder B is connected to the same MV bus but has a separate breaker and load. In the feeder-A-open snapshot, B can still receive power; its voltage and demand adjust to the changed circuit. The separate station auxiliary branch represents services such as controls and lighting; it is not a third customer feeder or a second main supply.

Engineering details

The two simultaneous balanced loads are constant impedances derived from their nominal power controls. The auxiliary branch is an invented unity-power-factor resistance consuming 10 kW at exactly 20 kV; actual auxiliary power also changes with bus voltage. The model sums complex branch-current phasors, so different phase angles are not blindly added as magnitudes. HV input real power equals delivered feeder power plus feeder resistive losses, transformer no-load/winding losses and auxiliary demand. Apparent power follows from the combined real/reactive pair; reactive magnetizing and leakage demand are omitted explicitly. The isolated snapshot has no main-network energy transfer; stored battery control energy is outside this steady-state AC ledger.

Checked sources: Schneider Electric: Installed apparent power (kVA); Short: Electric Power Distribution Handbook — authorized book preview; ABB: SPAD 346 C stabilized differential relay — YNyn0 application. Book reading: [R4], [R5].

8. Measurements, relay, station DC and trip mechanism

Measurement signals go to a protection relay in the control building. The relay decides whether to request a breaker trip. A station battery and charger provide control energy; the trip mechanism releases the breaker operating mechanism. These thin signal/control connections are separate from the thick three-phase power conductors.

Engineering details

Transformer differential protection compares properly referred currents on both sides of a defined protected zone; CT ratios, polarities and transformer connections matter. This is conceptual background: the model does not include a complete transformer differential CT zone, compensation or relay scheme. Real protection must account for external faults, CT error/saturation and transformer inrush. This lesson shows the chain measurements → relay decision → station-DC trip circuit → breaker mechanism, not numerical protection coordination. The relay does not interrupt the main current itself, and the small battery is not an HVDC converter. No pickup current, time delay, fault current, trip reliability or approved relay setting is inferred from this normal-operation model.

Checked sources: ABB: SPAD 346 C stabilized differential relay — YNyn0 application; ABB: Instrument Transformers — Technical Information and Application Guide; ABB: Distribution Automation Handbook — Elements of power distribution systems. Book reading: [R3], [R1].

9. Protective bonding, neutrals and the earth grid

Protective bonds join the transformer tank, switchgear enclosures and support steel to an earth grid. Neutral grounding has a different purpose and a separately labelled connection: it establishes a voltage reference to earth and affects earth-fault current behaviour, depending on the grounding arrangement. Cable screens and any overhead shield wire are also distinct from the three phase conductors. None is drawn as the normal load-energy return.

Engineering details

The assumed star neutrals are grounded, while the balanced three-wire feeder load has zero summed phase current and no intentional neutral load-current path. Unbalance, harmonics and earth-fault currents would change that picture and are not calculated. Protective-earth labels (PE), dashed bond lines, neutral labels N/n and the earth symbol complement colour. A fence, trenches, foundations and oil-containment outline show construction functions only. Earth-grid impedance, soil resistivity, transferred potential, touch/step voltage, lightning coverage, drainage/fire performance and structural strength remain unverified; the drawing is not evidence of personnel safety or standards compliance.

Checked sources: Schneider Electric: Earthing connections; ABB: SPAD 346 C stabilized differential relay — YNyn0 application; MIT / J. L. Kirtley: Polyphase Networks; National Grid: Overhead Line Conductor and Fittings. Book reading: [R1], [R3], [R5].

Why use a single bus—and what do we give up?

A single bus is easy to trace, but its shared equipment can interrupt both feeders. Opening feeder A does not create an alternative supply. Real stations may use additional transformers, bus sections or redundant supplies to improve continuity; those options require an explicitly connected architecture and protection assessment. They are not decorative additions to this scene.

A transformer changes AC voltage by magnetic coupling between insulated windings. In the selected YNyn0 connection both sides are star: each winding sees VLL/√3, so the ideal no-load winding turns ratio equals 110/20 = 5.5, with 0° phase displacement. That line-voltage/turns-ratio equality cannot be assumed for a star–delta connection. Both neutral leads are real connections; the balanced model has zero normal neutral current. Neither neutral grounding nor the visible earth mesh is a validated fault-safety design.

Editable, original learning assets

Blender uses metres and Z-up; glTF uses Y-up. The overview compresses line spans and site distances; internal windings, insulators and terminals are enlarged. Live parts are supported and separated from structural steel, but numerical insulation, mechanical, fire and earthing compliance has not been checked.

The model loads only after activation; individual cutaways load on demand. Use the viewer's five-second measurement to inspect foreground rendering on your device. Frame statistics are browser observations, not GPU benchmarks or engineering validation.

Book-led learning, traceable claims

The five books below define the curriculum. Specific accessible passages are identified; publisher metadata or contents alone are further reading, not verification of a passage. Manufacturer and university documentation supplements the books. All prose, geometry and diagrams are original.

  1. John D. McDonald (ed.). Electric Power Substations Engineering. 3rd edition, CRC Press, 2012. ISBN 9781439856383.

    Further reading: AIS bus arrangements, switching equipment, substation grounding, oil containment, protection and civil considerations. Publisher metadata and table of contents checked through indexed publisher content; individual technical passages were not accessible. Not passage-level evidence.

  2. John J. Winders. Power Transformers: Principles and Applications. Marcel Dekker, 2002; current publisher catalogue: CRC Press. ISBN 9780824707668.

    Further reading: two-winding connections, transformer losses and ancillary equipment. Publisher metadata and table of contents checked through indexed publisher content. Specific textbook passages not verified; no page numbers invented.

  3. J. Lewis Blackburn and Thomas J. Domin. Protective Relaying: Principles and Applications. 4th edition, CRC Press, 2014. ISBN 9781439888117.

    Further reading: relay input sources, system grounding, transformer/bus/line protection and trip-circuit design. Publisher metadata and table of contents checked through indexed publisher content. Relay settings and chapter passages not verified or reproduced.

  4. B. M. Weedy, B. J. Cory, N. Jenkins, J. B. Ekanayake and G. Strbac. Electric Power Systems. 5th edition, Wiley, 2012. ISBN 9780470682685.

    Further reading: three-phase systems, transformers, power flow, substations and protection. Publisher metadata and table of contents checked. The publisher's sample link could not be retrieved; no technical passage treated as checked.

  5. T. A. Short. Electric Power Distribution Handbook. 2nd edition, CRC Press, 2014. ISBN 9781466598652.

    Checked book foundation for station/feeder functions and loss categories; broader transformer and grounding chapters remain further reading. Publisher metadata/table of contents and the separately linked authorized preview passages (§1.4 and §1.8) checked. Other chapters were not inspected.

Accessible supporting evidence

  • Short: Electric Power Distribution Handbook — authorized book preview

    Book-led foundation: distribution substations and outgoing feeders; relayed breakers; distinct conductor, transformer load and no-load losses. None of the book's equipment ratings or loss percentages are assigned to this example. Text checked in §1.4, printed pp. 15–18, and §1.8, printed pp. 25–28. Publisher-copyrighted preview served by a bookseller; no illustrations reproduced. Checked 2026-10-04.

  • MIT / J. L. Kirtley: Polyphase Networks

    Balanced three-phase systems, line/phase voltages, ideal transformer relations and winding connections. Some note equations use peak phasors; this lesson consistently uses RMS. Accessible course-note PDF checked: Three Phase Systems, Line-Line Voltages, Transformers and Three-Phase Transformers sections. The notes are dated 2003 and hosted in the Spring 2011 course. Checked 2026-10-04.

  • Schneider Electric: Installed apparent power (kVA)

    Balanced three-phase apparent-power/current relationship, power factor and distinction between phase-to-neutral and phase-to-phase voltage. This is Schneider's Electrical Installation Guide, not Wikipedia. Accessible formula text checked; no equipment-sizing tables adopted. Checked 2026-10-04.

  • ABB: SPAD 346 C stabilized differential relay — YNyn0 application

    A real YNyn0 application with grounded star points; differential protection concept and auxiliary/trip connections. It does not specify this lesson's 110/20 kV transformer or approve its grounding. Example 1 / Fig. 7, printed p. 21, and explanatory text on printed p. 25 checked. Differential-principle description on printed p. 4 also checked. Relay settings are deliberately not reproduced. Checked 2026-10-04.

  • Gass: transformer vector-group notation

    Manufacturer explanation of YNyn0 as separate star-connected windings with brought-out neutral points; not evidence that this is a universal HV/MV arrangement. Vector Group (three-phase transformers) table and definition checked. Checked 2026-10-04.

  • MIT / J. L. Kirtley: Magnetic Circuit Analog to Electric Circuits

    Magnetic flux guided by ferromagnetic material and voltage induced by changing flux; distinguishes magnetic coupling from a conducting connection between windings. Accessible note PDF, Introduction and Faraday's Law and Inductance sections checked. No magnetic field solver is implemented here. Checked 2026-10-04.

  • ABB: Instrument Transformers — Technical Information and Application Guide

    Current-transformer primary in series, voltage-transformer primary in parallel, secondary measurement/protection purpose and open-CT-secondary hazard. Printed pp. 4–5 / Fig. 2 connection explanation and printed p. 26 open-circuit warning checked. Diagram and ratio values are not copied. Checked 2026-10-04.

  • Hitachi Energy: Disconnectors

    Isolation function and restricted switching duties of disconnectors, distinct from circuit breakers. No manufacturer's compliance statement is transferred to this educational geometry. Applications section checked: isolation; very small currents or insignificant terminal-voltage change. Checked 2026-10-04.

  • Hitachi Energy: Air-insulated switchgear portfolio

    Recognizable AIS equipment families: circuit breakers, instrument transformers, disconnectors and surge arresters. Product ratings are not assigned to the scene. Primary-substation equipment portfolio description checked. Checked 2026-10-04.

  • ABB: Distribution Automation Handbook — Elements of power distribution systems

    Outdoor HV AIS / indoor MV arrangement, single-transformer bus limitations, surge protection, oil/radiator cooling and station DC functions. Not specifications for this scene. Prototype handbook 1MRS757959: printed pp. 4–6, 12–13, 32 and 97–98 checked. Manufacturer educational guidance, not design certification. Checked 2026-10-04.

  • Schneider Electric: Functions of the substation with MV metering

    General protection, metering and outgoing-feeder panel functions. This consumer MV/LV document supports functions, not this invented HV/MV station's physical design. Metering and Simplified electrical network diagram explanatory text checked; no original illustration reproduced. Checked 2026-10-04.

  • ABB Review 1/2004: vacuum interrupters

    MV vacuum-interrupter stem, bellows, contacts, insulating envelope and AC current-zero interruption principle. Not the separate HV breaker's gas/interruption design. Printed pp. 22–23, component key and contact-separation/current-zero explanation checked. Checked 2026-10-04.

  • ABB Review 1/2007: The circuit breaker — SF6 interruption principle

    SF6 insulation, nozzle-directed gas cooling and gas flow near AC current zero in an HV breaker context. The scene does not implement a full puffer or self-blast mechanism. Printed pp. 77–78 and Fig. 6 component/sequence caption checked. No figure, product ratings, pressures or interruption times copied. Checked 2026-10-04.

  • Hitachi Energy: SF6 environmental impact and alternative high-voltage technology

    SF6's greenhouse-gas tradeoff and existence of alternative HV gas technologies. No numerical climate metric, product-performance claim or retrofit instruction adopted. Article dated 3 July 2023: greenhouse-gas description, insulation/current-interruption role and alternative-technology paragraphs checked. Checked 2026-10-04.

  • Hitachi Energy: liquid-filled transformer construction

    Laminated core, conductor windings, tanks, radiators and optional fans. The product page concerns a lower-voltage range: it supports component recognition, not the illustrated 110 kV insulation/rating. Construction paragraph checked; no product dimensions, efficiency or compliance claim used. Checked 2026-10-04.

  • National Grid: Overhead Line Conductor and Fittings

    Insulators, conductor attachments, suspension/tension fittings and a shield wire's separate lightning/fault function. Not a clearance or tension design for this scene. December 2019 document, §2 Introduction and §2.1 Conductors, printed p. 5, checked. Checked 2026-10-04.

  • National Grid: hot-weather advice

    Overhead conductors expand and sag more in heat. The scene's sag is a visual curve, not a solved catenary or verified mechanical load case. Accessible overhead-line temperature/sag explanation checked. Checked 2026-10-04.

  • Schneider Electric: Earthing connections

    Definitions of protective conductor, exposed conductive part and equipotential bonding. This LV-context guide does not validate an HV substation earth grid or touch/step voltages. Definitions and purpose of protective bonding checked; no standard-compliance claim made. Checked 2026-10-04.