چەندین پێشی ئەرێنی گەڕانی بەرزدەرەوەی جاری دایەک (HVDC) لە سەر گەڕانی بەرزدەرەوەی جاری ئەلکتریکی ئاسایی (HVAC) لە گەڕانی نەرخ؟

DC bi hêvî vê AC de çend piştînên?

Dengê ji navberên derbasdar çend mijil çêtir dike pêşî çawa ku bi karîbere. Pargîran, ku herêmîn digire, dengê ji nav miyilên çêtir û çend substationan da dest pê kirin. Dengê bi hêvî bi rêzikî yên verastî werdigire, bi karîbere AC û DC bikar anîn. Heta AC bi rûniya polandeyên bajar û kawetên malîkane digire, DC bi hêvî wekî piştînên bijîn dikare di şevikina dengê de.

Bijîkeriya şevikina dengê ya min rekeş û maliyayên were radkirin. Heta ji bo her du taybetmendiyên dema çendên, DC bi hêvî piştînên çêtir dikare. Vê gotar bi serîyan DC bi hêvî yên bi AC:

Maliyayên Şevikina Bi Rêzikî
Maliyayên şevikina li ser tarzeya hêvî, cihazên guhertina hêvî, çendîna/kubîna lîne, demên tower û rekesên werdigire. AC transformers bikar anîn bi guherandina hêvî - bi hêvî û bi maliyayên yekêmî yên DC bi thyristor-based converters, wê tenê maliyayên yekêmî yên wê.

AC pirsa lîne yên sêfaseyî hewce dike. DC, bi karîbere zemin bi rêzikî, lîne yên yek (monopolar) û du (bipolar) bikar anîn, maliyayên were radkirin. Lîne yên sêfaseyî heta dikarin bi hêvî yên yekêmî yên DC double bipolar links dengê du ên dikare berde.

AC hewce dike demên mezin faza-bi-zemin û faza-bi-faza, towerên gir û ber bi hêvî. Towerên DC maliyayên wereguherandina were radkirin. DC bi hêvî yên rekesên şevikina were radkirin, wê bi hêvî yên yekêmî yên AC.

Maliyayên guhertina guhertina hêvî bi du kategorî yên serokî: maliyayên istasyona terminal û maliyayên lîne yên şevikina. Yekemî maliyayên bi hêvî, bi hêvî yên navendî yên şevikina, divê were radkirin, dike ra maliyayên din bi hêvî yên lîne. Maliyayên terminal AC bi hêvî yên yekêmî, lê maliyayên terminal DC bi hêvî yên mezin. Lê, maliyayên her 100 km bi hêvî yên lîne yên şevikina AC bi hêvî yên yekêmî yên lîne yên DC. Dema ku, maliyayên guhertina guhertina AC û DC di navendek bi hêvî yên break-even distance de.

Break-even distance ya navendek dike ku maliyayên guhertina guhertina AC bi hêvî yên DC. Divê navendek bi serîyan rêzikî yên şevikina: navendek di navendek 400-500 miles (600-800 km) de (bi hêvî yên overhead lines), 20-50 km (bi hêvî yên underwater lines), û 50-100 km (bi hêvî yên underground lines). Di navendek de, DC bi hêvî yên yekêmî û ekonomîkî yên şevikina dengê.

Şevikina DC bi hêvî yên rekesên were radkirin bi hêvî yên AC, bi hêvî yên serokî yên serokî:

Absence of Reactive Power Losses

Şevikina AC rekesên reactive power losses, ku bi hêvî yên navendek, frequency, û inductive loads at the receiving end. Rekesên were radkirin effective power transfer û waste energy, limiting the maximum length of efficient HVAC lines. To mitigate this, HVAC systems rely on series and shunt compensation to reduce VARs (volt-ampere reactive) and maintain stability.

In contrast, HVDC operates without frequency or charging current, eliminating reactive power losses entirely. This removes the need for such compensation measures.

Reduced Corona Losses

When transmission voltage exceeds a critical threshold (the corona inception voltage), air molecules around conductors ionize, creating sparks (corona discharge) that waste energy. Corona losses depend on voltage level and frequency. Since DC has zero frequency, HVDC corona losses are roughly one-third of those in HVAC systems.

Absence of Skin Effect

AC current exhibits the skin effect, where current concentrates near the conductor surface, leaving the core underutilized. This uneven current distribution reduces the effective cross-sectional area of the conductor, increasing resistance (as resistance is inversely proportional to area) and resulting in higher I²R losses in HVAC lines. HVDC, with its steady direct current, avoids this effect, ensuring uniform current distribution across the conductor and minimizing resistive losses.

No Radiation or Induction Losses

HVAC transmission lines suffer from radiation and induction losses due to their constantly varying magnetic fields. Radiation losses occur because long AC lines act like antennas, radiating energy that is irrecoverable. Induction losses arise from currents induced in nearby conductors by the alternating field.In HVDC systems, the magnetic field is constant, eliminating both radiation and induction losses entirely.

Reduced Charging Current Losses

Underground and underwater cables have inherent parasitic capacitance, which requires charging before they can transmit power. Capacitance increases with cable length, and thus charging current rises proportionally.

In AC systems, cables charge and discharge 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.

No Dielectric Heating Losses

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) Thinner Conductors

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) Line Length Limitations

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) Reduced Cable Rating Requirements

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) Narrower Right-of-Way

"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.