Quae Sunt Differentiae Inter HVAC et HVDC in Transmissione Electricitatis

Differencia Inter HVAC et HVDC

Electricitas generata in stationibus electricis per longas distancias ad substationes electricas transmittitur, quae deinde distribuunt eam ad consumidores. Tensio utilis ad transmissionem electricitatis per longas distancias est extrema, et causas huius altae tensionis postea explorabimus. Praeterea, potestas transmissa esse potest vel in forma currentis alternantis (CA) vel directi (CD). Itaque, potestas transmitti potest utendo vel HVAC (High Voltage Alternating Current) vel HVDC (High Voltage Direct Current).

Cur Alta Tensio Necessaria Est ad Transmissionem?

Tensio partem crucialem ludit in reductione linealium amissionum, alias nominatarum amissionibus transmissionis. Omnis conductor electricus utilis ad transmissionem electricitatis habet certam quantitatem resistentiae ohmicae (R). Quando currentis (I) per hos conductores fluunt, generant energiam thermicam, quae est essentialem energiam amissam vel potentiam (P).

Secundum Legem Ohm

Ut patet, energia in conductore amissa durante transmissione dependet a currenti magis quam a tensione. Verumtamen, possumus magnitudinem currentis per conversionem tensionis usque ad speciale equipmentum.

Durante conversionem tensionis, potestas conservatur et immutata manet. Simpliciter variat inversa proportionis factoribus, secundum principium:

Exempli gratia, 11KW potestas ad tensione 220v habet 50 Amps. In talibus casibus, amissiones lineales erunt

Augeamus tensionem decuplo. Itaque, idem 11KW potestas haberet tensionem 2200v & 5 Amps. Nunc amissiones lineales essent;

Ut vides, auctio tensionis significanter reducit amissiones potestatis in lineis transmissionis. Itaque, ut diminuamus currentem in cabulis transmissionis, dum eandem quantitatem potestatis transmissionis servamus, augemus tensionem.

Bellum Currentium (CA vs. CD)

In fine 1880, tempore dicto "Bellum Currentium," directus currentis (CD) fuit primus adhibitus ad transmissionem potestatis. Verum tamen, inefficiens reputatus est propter defectum practicarum machinarum conversionis tensionis - contra currentem alternans (CA), qui facile poterat auctus vel reductus esse per transformatores. Primi statones potestatis CD low-voltage tantum poterant suppeditare electricitatem intra radios paucorum milliarum; ultra hoc, tensio vehementer caderet, requirere plures statones generantes in parvis regionibus - approach costosus.

Quamquam transmissionem DC altae tensionis inherentiter minores amissiones incurrit quam CA, systemata DC primitiva dependerent a valvulis arcus mercurii (rectificatoribus) ad convertere AC altae tensionis in DC ad longinquam transmissionem. Haec terminalia dispositiva erant ingruenta, cara, et frequentem manutentionem requirebant. Contra, transmissionem CA dependebat a transformatoribus - plus efficacibus, aequabilioribus, et fidelioribus - faciens CA electionem dominantem ad longinquam transmissionem potestatis tempore illo.

Cum inter high-voltage AC (HVAC) et high-voltage DC (HVDC) ad transmissionem eligendum sit, varios factores criticos considerari debent. Hoc articulus haec factores in detali explorat.

HVAC & HVDC

HVAC (High Voltage Alternating Current) et HVDC (High Voltage Direct Current) referuntur ad ranges tensionis utilis ad longinquam transmissionem potestatis. HVDC typice preferetur pro ultra-longinquis distantiis (solito supra 600 km), tamen utrumque systema hodie latissime usitat sunt in toto orbe, singula cum suis propriis praediis et inconvenientiis.

Costus Transmissionis

Longinquam transmissionem potestatis altae tensionis requirit, cum potestas transfertur inter stationes terminales quae se occupant conversionis tensionis. Totus costus transmissionis itaque dependet ex duobus componentibus: costus stationum terminalium et costus linealis.

• Stationes Terminales
  Stationes terminales convertunt niveles tensionis ad transmissionem. Pro systematibus CA, hoc principaliter fit per transformatores, qui commutant inter alta et bassa tensiones. Pro systematibus CD, stationes terminales utuntur converteribus thyristor vel IGBT-based ad adjustare niveles tensionis DC.

  Cum transformatores sint plus fideles et cariores quam converteres solid-state, stationes terminales CA sunt minus carae quam earum contrapartes DC, faciens conversionem tensionis CA plus oeconomicam.

• Lineae Transmissionis
  Costus lineales dependet a numero conductorum et designo turrium transmissionis. Systemata HVDC requirunt tantum duo conductores, systemata HVAC autem requirunt tres vel plures (includentes conductorum bundlos ad mitigandum effectus corona).

  Turres transmissionis CA debent supportare graviores onera mechanicis, requirere fortiores, altiores, et latiores structuras comparatis turribus HVDC. Costus lineales crescunt cum distantia, et per 100 km, lineae HVAC sunt significanter cariores quam lineae HVDC.

• Totus Costus Transmissionis
  Totus costus determinatur a costibus terminalis (fixis, independenter ab distantia) et costibus linealibus (variabilibus, crescendo cum distantia). Itaque, totus costus systematis transmissionis crescit cum distantia.

Distantia Break-Even

"Distantia break-even" refert ad longitudinem transmissionis ultra quam totus costus investimenti HVAC superat illud HVDC. Haec distantia est circa 400-500 milia (600-800 km). Pro distantiis ultra hanc limen, HVDC est electio plus oeconomicum; pro distantiis brevioribus, HVAC est plus oeconomicum. Haec relatio visibiliter illustratur in grapho supradicto.

Flexibilitas

HVDC typice adhibetur pro puncto-ad-punctum longinquam transmissionem, cum extrahendi potestas in punctis intermediis requireret expensivos converteres ad redigere altas tensiones DC. Contrario, HVAC offert maiorem flexibilitatem: plures stationes terminales possunt uti transformeribus aequabilioribus ad redigere altas tensiones, permittendo extractionem potestatis in diversis punctis per lineam.

Amissiones Potestatis

Transmissionem HVAC incurrit varios genera amissionum, includentes amissiones corona, effectus cutis, amissiones radiationis, et inductionis, quae sunt largiter absentia vel minimizata in systematibus HVDC:

• Amissiones Corona: Quando tensio excedit certum limen, aer circumdans conductores ionizatur, creando scintillas (discharge corona) quae dissipant energiam. Haec amissiones sunt dependentes a frequencia - cum DC habeat frequenciam nullam, amissiones corona HVAC sunt circa tripla maiora quam in HVDC.

• Effectus Cutis: In transmissione CA, densitas currentis maxima est ad superficie conductoris et minima ad nucleo (effectus cutis), reducens aream sectionalem effectivam utilitati currentis. Hoc auctificat resistentiam conductoris et amplificat amissiones I²R. Currentis CD, contra, distribuit uniformiter per conductor, eliminans hunc effectum.

• Amissiones Radiationis et Inductionis: Magneticum alternans field HVAC causa longas lineas agere sicut antennae (radiantes energiam irrecoverabile) et inducent currentes in conductoribus vicinis (amissiones inductionis). Steady magneticum field HVDC evitat ambas difficultates.

Effectus Cutis

Effectus cutis, directe proportionalis ad frequenciam, cogit maior partem currentis CA fluere iuxta superficiem conductoris, relicto nucleo underutilized. Hoc reducit efficientiam conductoris: ad portandum maiores currentes, systemata HVAC requirunt conductoribus cum majori area sectionali, auctificans costus materialis. HVDC, non affectus ab effectu cutis, utitur conductoribus plus efficaciter.

Itaque, ad portandum idem currentem, HVAC requirit conductoribus cum maior diametro, HVDC autem potest hoc effici cum minori diametro conductoris.

Ratings Currens et Tensionis Cables

Cables habent rated maximum tolerabilis tensionis et currentis. Pro CA, peak voltage et current sunt circa 1.4 times higher quam eorum medii valores (qui correspondent ad actual delivered power vel equivalent DC values). Contra, systemata DC habent identicos peak et medii valores.

Tamen, conductor HVAC debet rated for peak current et voltage, wasting approximately 30% of their carrying capacity. Contra, HVDC utilizes the full capacity of conductors, meaning a conductor of the same size can transmit more power in HVDC systems.

Right-of-Way

"Right-of-way" refers to the land corridor required for transmission infrastructure. HVDC systems have a narrower right-of-way due to smaller towers and fewer conductors (two for DC vs. three for three-phase AC). Additionally, AC insulators on towers must be rated for peak voltages, further increasing their footprint.

This narrower corridor reduces material, construction, and land costs, making HVDC superior in terms of right-of-way efficiency.

Submarine Power Transmission

Submarine cables used for offshore power transmission have stray capacitance between parallel conductors. Capacitance reacts to voltage changes—constant in AC (50–60 cycles per second) but only occurring during switching in DC.

AC cables continuously charge and discharge, causing significant power losses before delivering power to the receiving end. HVDC cables, charged only once, eliminate such losses. For more details, refer to content on submarine cable construction, characteristics, laying, and joints.

Controllability of Power Flow

HVAC systems lack precise control over power flow, whereas HVDC links use IGBT-based semiconductor converters. These complex converters, switchable multiple times per cycle, optimize power distribution across the system, improve harmonic performance, and enable rapid fault protection and clearance—advantages unmatched by HVAC.

Interlinking Asynchronous Systems and Smart Grids

A smart grid allows multiple generating stations to feed into a unified network, leveraging small-scale grids for high-power generation. However, connecting multiple asynchronous AC grids (with differing frequencies or phases) is highly challenging.

Interlinking Asynchronous Grids

Power grids worldwide operate at different frequencies—some at 50 Hz, others at 60 Hz. Even grids with the same frequency may be out of phase. These are classified as "asynchronous systems" and cannot be connected via standard AC links.

DC, however, is unaffected by frequency or phase. HVDC interlinks resolve this by converting AC to frequency- and phase-agnostic DC, enabling seamless integration of asynchronous grids. At the receiving end, HVDC inverters convert the DC back to AC with the required frequency, facilitating unified power transmission.

Circuit Breakers

Circuit breakers are critical in high-voltage transmission, responsible for de-energizing circuits during faults or maintenance. A key requirement is arc-extinguishing capability to interrupt power flow.

• HVAC Circuit Breakers: AC current reverses direction continuously, creating natural zero-current moments (50–60 times per second) that automatically extinguish arcs. This "self-extinguishing" feature simplifies HVAC breaker design, making them relatively straightforward and cost-effective.

• HVDC Circuit Breakers: DC current is unidirectional with no natural zero crossings. To extinguish arcs, specialized circuitry must artificially generate zero-current points. This complexity makes HVDC breakers more intricate and expensive than their AC counterparts.

Generation of Interference

AC's alternating current produces a constantly varying magnetic field, which can induce interference in nearby communication lines. In contrast, DC's steady magnetic field eliminates such interference, ensuring minimal disruption to adjacent communication systems.