Cad é na Buntáistí atá ag HVDC níos mó ná HVAC i dTraisfhuascailt Eolais?

Cé acu na Buntáistí atá ag HVDC níos mó ná HVAC?

Glanann an t-ileachtagh airgid fada cosáin roimh é a shroich intreabhaithe. Foraíonn stáisiúin gineadóireachta, go minic, ar fud tíortha, ag iarraidh leictreachais trí chéad míle agus tríd iolra oifigí meascánacha. Léiríonn an ileachtagh ar mhodh ard-sprioc go díreach laghdú ar chailleadh líne, ag úsáid an AC agus an DC. Cé go bhfuil an AC coitianta ag baint úsáide as pólai agus boird sa bhaile, tá buntáistí uathúla ag an HVDC in ileachtagh cumhacht.

Is é sprioc an ileachtagh cumhacht ná laghdú ar chostais agus ar chailleacháin. Cé go bhfuil tionchar ag an dá modh, tá níos mó buntáistí ag an HVDC. Scrúdóidh an alt seo na buntáistí atá ag an HVDC níos mó ná HVAC:

Costais Ileachtagha Níos Íse
Bhunú costais ileachtagha ar thacaíocht eochairsprioc, ar líon/maidhm cunduitore, ar mheastacháin toraidhe, agus ar chailleacháin. Úsáideann an HVAC trasnóir do thacaíocht - níos simplier agus ísle ná an HVDC a úsáideann thyristor-based converters, a bhfuil ainscostais aige.

Níos mó ná 3 cunduitore ag teastáil don HVAC do thransmha 3-phás. Úsáideann an HVDC an talamh mar pháth náisiúnach, ag úsáid 1 (monopolar) nó 2 (bipolar) cunduitore, ag laghdú ar chostais. Is féidir le 3-phás cunduitore a dhéanamh dubailte an cumhacht trí HVDC double bipolar links.

Níos mó spás phase-to-ground agus phase-to-phase atá riachtanach don HVAC, ag cruthú toraidhe níos airde agus níos leata. Laghdú ar chostais istallacháin ag toraidhe HVDC. Tá cailleacháin ileachtagha níos ísle ag an HVDC, ag déanamh é níos cruinne.

Is féidir costais ileachtagha iomlán a roinnt i dtreo dhá catagóir: costais eochairstáisi agus costais líne. Is costas seasta é an chéad cheann, neamhspleách ó fhad an ileachtagha, agus is é an dara ceann a athraíonn le fad an líne. Is íse costais eochairstáisi AC, ach is airde go mór costais eochairstáisi HVDC. Ach, is airde go mór an costas per 100 km don HVAC ná don HVDC. Mar sin, téann línte costais iomlána HVAC agus HVDC crois ag pointe aithnid mar an break-even distance.

Is é an break-even distance an fhad ileachtagha a thugtar ar an suim iomlán a bhuailt ar HVAC níos airde ná an HVDC. Athraíonn an fhad seo de réir cineál an ileachtagha: go faid 400-500 míle (600-800 km) do línte os comhair, 20-50 km do línte faoi uisce, agus 50-100 km do línte faoi talamh. I ndiaidh an fhad seo, bíonn an HVDC rogha níos cruinne agus níos feidhmeach ó thaobh geilleagartha de do ileachtagh cumhacht.

Tá cailleacháin níos ísle ag an ileachtagh HVDC ná ag an HVAC, le forbairtí rí-thábhachtacha sna réimsí seo leanas:

Féachaint ar Chailleacháin Neamhchoitianta

Tá cailleacháin neamhchoitianta ag an ileachtagh HVAC, atá dírecte proporcionalta le fad an líne, fréamhaithe, agus ladáin indachtacha ag an taobh foghlaim. Díolann na cailleacháin seo laghdú ar an gcumhacht a thugtar agus a dhíol, ag cur teoiricí ar theorainn an fhad HVAC líne. Chun an t-ábhar seo a laghdú, bronnann córais HVAC ar chomhbhrúch series agus shunt compensation le haghaidh laghdú VARs (volt-ampere reactive) agus cosaint stabacht.

In ainneoin, níl fréamhaithe ná siúlú cúrsa ag an HVDC, ag díol cailleacháin neamhchoitianta go hiomlán. Seo a bhaint amach an riachtanas leis na beartais seo.

Laghdú ar Chailleacháin Corona

Nuair a tharla an sprioc sprioc (an corona inception voltage), ionóidh molécáil aer timpeall cunduitore, ag cruthú scintillation (corona discharge) a dhíolann cumhacht. Bhíonn cailleacháin corona bunaithe ar sprioc sprioc agus fréamhaithe. Ó díolann DC zero fréamhaithe, is triúr den chuid cailleacháin corona HVAC atá ag an HVDC.

Féachaint ar Eifeacht Skin

Léiríonn an currant AC an skin effect, áit a mbíonn an currant bunaithe ar an gcunduitur surface, ag fágáil an lár gan úsáid. An t-eifeacht neamhchoitianta seo laghdú ar an gcross-sectional area a bhíonn ann, ag ardú resistance (mar tá resistance inversely proportional to area) agus ag déanamh I²R losses níos airde sa HVAC lines. An HVDC, leis an currant díreach, ní léiriann sé an t-eifeacht seo, ag déanamh cinnte go bhfuil an currant coitianta bunaithe ar an gcross-sectional area, ag laghdú ar chailleacháin resistance.

Gan Cailleacháin Radharcach nó Induction

Tá cailleacháin radharcach agus induction ag línte ileachtagha HVAC de bharr a magnetic fields go leanúnach. Téann cailleacháin radharcach ar aghaidh mar gheall ar éirisí AC líne a bheith cosúil le antanna, ag radharcach energy nach féidir a athshroich. Téann cailleacháin induction ar aghaidh ó currents induced in nearby conductors by the alternating field.Sa chuid HVDC systems, is constant an magnetic field, ag díol cailleacháin radharcach agus induction go hiomlán.

Laghdú ar Chailleacháin Siúlú Cúrsa

Tá capacitance parásach inherent in underground and underwater cables, which requires charging before they can transmit power. Téann capacitance ar aghaidh le fad an cable, agus mar sin téann an currant siúlú cúrsa ar aghaidh proportionally.

Sa chuid AC systems, charge agus discharge cables multiple times per second, drawing additional current from the source to maintain this cycle. This extra current increases I²R losses in the cable.HVDC cables, however, only require charging once during initial energization or switching. This eliminates losses associated with continuous charging currents.

Gan Cailleacháin Dielectric Heating

The alternating electric field in AC systems affects insulation materials in transmission lines, causing them to absorb energy and convert it into heat—a phenomenon known as dielectric loss. This not only wastes energy but also shortens insulation lifespan.HVDC systems generate a constant electric field, avoiding dielectric losses and the associated insulation heating issues.

3) Conductors Níos Fíní

The skin effect in AC causes current to concentrate near the conductor surface, requiring thicker conductors to increase surface area and accommodate higher currents.HVDC, free from the skin effect, allows current to distribute uniformly across the conductor cross-section. This enables the use of thinner conductors while maintaining the same current-carrying capacity, reducing material costs and weight.

4) Teorainn Fad an Líne

HVAC lines suffer from reactive power losses that increase directly with line length. This imposes a critical limit on HVAC transmission distance: beyond approximately 500 km for overhead lines, reactive power losses become excessively high, destabilizing the system.HVDC transmission, by contrast, has no such length restrictions, making it suitable for ultra-long-distance power delivery.

5) Laghdú ar Riachtanais Raite Cable

Cables are rated for maximum tolerable voltage and current. In AC systems, peak voltage and current are roughly 1.4 times higher than their average values (which correspond to actual power delivered). However, conductors must be rated for these peak values.In DC systems, peak and average values are identical. This means HVDC can transmit the same power using cables with lower voltage and current ratings compared to HVAC. In fact, HVAC systems effectively waste about 30% of a conductor’s capacity due to their higher peak requirements.

6) Right-of-Way Níos Caol

"Right-of-way" refers to the land corridor required for transmission infrastructure. HVDC systems require a narrower right-of-way because they use smaller towers and fewer conductors.HVAC, by contrast, needs taller towers to support more conductors and larger insulators (rated for AC peak voltages), which demand stronger structural support. This broader footprint increases material, construction, and land costs—making HVDC superior in terms of right-of-way efficiency.

7) Superior Cable-Based Transmission

Underground and submarine cables consist of multiple conductors separated by insulation, creating parasitic capacitance between them. These cables cannot transmit power until fully charged, and capacitance (and thus charging current) increases with length.AC systems repeatedly charge and discharge cables (50–60 times per second), amplifying I²R losses and limiting cable length. HVDC cables, however, only charge once (during initial energization or switching), eliminating such losses and length restrictions.This makes HVDC the preferred choice for offshore, underwater, and underground cable transmission.

8) Bipolar Transmission

HVDC supports versatile transmission modes, with bipolar transmission being a widely used and cost-effective option. It features two parallel conductors with opposite polarities, their voltages balanced relative to the earth.If one line fails or breaks, the system seamlessly switches to monopolar mode: the remaining line continues supplying current, using the earth as the return path.

9) Controllable Power Flow

HVDC converters, based on solid-state electronics, enable precise control over power flow in AC networks. Their rapid switching capability (operating multiple times per cycle) enhances harmonic performance, dampens power swings, and optimizes the network’s power supply capacity.

10) Fast Fault Clearance

Fault currents—abnormal currents from electrical faults—pose significant risks. In HVAC systems, high fault currents can damage transmission lines, stations, generators, and loads.HVDC minimizes such risks: fault currents are lower, limiting damage to specific sections, and its fast-switching operation ensures rapid fault response, enhancing system resilience.

11) Asynchronous Grid Interconnection

HVDC enables interconnection of asynchronous AC grids with differing parameters (e.g., frequency, phase).Regions often use distinct frequencies (e.g., 50 Hz in Europe vs. 60 Hz in the U.S.), and grids may have phase differences, making direct AC interconnection impossible. HVDC, operating without frequency or phase constraints, easily links these independent systems.

12) Enabling Smart Grids

Smart grids integrate small-scale generators (solar, wind, nuclear) into a unified network with intelligent power flow control.This is feasible with HVDC, which supports asynchronous interconnection of generation units and provides full control over power distribution, aligning with smart grid requirements.

13) Reduced Noise Interference

HVDC causes far less noise interference to nearby communication lines compared to HVAC.HVAC generates audible buzzing, radio, and TV interference, with intensity tied to its frequency. HVDC, with zero frequency, produces minimal noise. Additionally, HVAC noise increases in bad weather, while HVDC noise diminishes, ensuring more stable operation.