SUNCABLE PROJECT - AUSTRALIA - SINGAPORE

Australian company Sun Cable plans to develop, the world's largest, a massive 12,400-hectare solar farm and transport electricity to the northern city of Darwin via an 800-kilometer (497-mile) overhead transmission line. From Darwin, the electricity will be transmitted to Singapore via three 4,300-kilometer-long high voltage submarine cables.

The Australia-Asia PowerLink project aims to deliver up to 2 gigawatts of electricity annually to Singapore and 4GW of electrical power locally. According to Australian Prime Minister Anthony Albanese "A project like Sun Cable which has the potential to export clean energy to Singapore is the ultimate win-win." and provide a significant boost to the economy, at an estimated cost of 29 billion AUD.

Something though is bothering the OHM's Law -

Calculating Cable Resistance

The impedance of a cable $R$ can be calculated using the formula:

$$R = \rho \times \frac{L}{A}$$

Where:

• $\rho$ = Resistivity of copper = $1.68 \times 10^{-8} \, \Omega \cdot m$
• $L$ = Length of the cable = 4,300 km = 4,300,000 m
• $A$ = Cross-sectional area of the conductor (assuming 1,500 mm² for high-voltage copper cables)

Substituting the values:

$$R = 1.68 \times 10^{-8} \times \frac{4,300,000}{1,500 \times 10^{-6}} = 48.16 \, \Omega$$

Calculating Current

The current $I$ in the cable can be calculated using the formula:

$$I = \frac{P}{V}$$

Where:

• $P = 2 \, GW = 2,000,000,000 \, W$
• $V = 425 \, kV = 425,000 \, V$

Substituting the values:

$$I = \frac{2,000,000,000}{425,000} = 4,706 \, A$$

Calculating Power Loss

The power loss $P_{loss}$ due to resistance is given by:

$$P_{loss} = I^2 \times R$$

Substituting the values:

$$P_{loss} = (4,706)^2 \times 48.16 \approx 1.06 \times 10^9 \, W = 1.06 \, GW$$

Percentage Loss Calculation

To find the percentage loss relative to the total power transmitted:

$$\text{Percentage Loss} = \frac{P_{loss}}{P_{transmitted}} \times 100 = \frac{1.06 \, GW}{2 \, GW} \times 100 \approx 53\%$$

Conclusion with Copper Cable:

• Total Power Loss: Approximately 1.06 GW
• Percentage of Power Lost: About 53%

POWER LOSS 1 x 4300km COPPER ≈ 53% (1.06 GW)

POWER LOSS 3 x 4300km (12900km) COPPER ≈ 17.67% (353.3 MW)

SOLUTIONS REDUCING POWER LOSSES: 

Overview of the SIEMENS HVDC Plus VSC, MMC, and HVDC Technologies:

• VSC (Voltage Source Converter): An advanced type of converter used in HVDC systems that allows for precise control of power flow and voltage. VSCs have improved efficiency compared to older Line Commutated Converters (LCC).
• MMC (Modular Multilevel Converter): A specific type of VSC that offers even better efficiency, lower losses, and higher reliability. MMC is currently the state-of-the-art technology for HVDC applications.

Power Loss Components in HVDC Systems Using VSC/MMC:

1. Converter Losses: Losses occurring in the converters (rectifier and inverter stations) due to switching, conduction, and control operations.
2. Transmission Line Losses: Resistive losses in the cables themselves, dependent on the cable material, length, and cross-sectional area.
3. Other Losses: Minor losses due to filters, cooling systems, and auxiliary equipment.

Estimated Power Losses with VSC/MMC in a 4,300 km HVDC System:

1. Converter Losses (VSC/MMC):

   • Typical loss range for VSC/MMC converters is about 1-2% of the total transmitted power per station.
   • For a two-station system (rectifier and inverter), losses are typically around 2-4%.

2. Transmission Line Losses:

   • For an HVDC cable using aluminum or copper, losses primarily depend on the cable's resistance.
   • Advanced HVDC systems with optimized converters (VSC/MMC) typically have lower overall resistive losses due to improved current control.
   • Assuming resistive losses of about 3-5% for a high-efficiency system over 4,300 km, which is lower compared to traditional systems.

3. Total System Losses:

   • Combined converter and transmission losses for a VSC/MMC HVDC system are usually in the range of 5-9%.

Percentage Loss Calculation for a 2 GW System:

1. Assuming Total Losses: 7% (Midpoint Estimate)

   • Total Power Loss = 7% of 2 GW
   • $P_{loss} = 0.07 \times 2,000 \, \text{MW} = 140 \, \text{MW}$

2. Power Delivered to End-User:

   • $P_{delivered} = 2,000 \, \text{MW} - 140 \, \text{MW} = 1,860 \, \text{MW}$

Conclusion:

• Percentage Loss with VSC/MMC HVDC System: Approximately 5-9% depending on the specific system design and conditions.
• Advantages Over Traditional HVDC: These systems offer lower losses, improved control, and higher reliability, making them more efficient for long-distance power transmission, especially for integrating renewable energy sources.

POWER LOSS 4300km SIEMENS VSC/MMC SYSTEM ≈ 8% (160 MW)

POWER LOSS 3 x 4300km SIEMENS VSC/MMC SYSTEM ≈ 5.33% (106.67 MW)

Maintenance of VSC (Voltage Source Converter) and MMC (Modular Multilevel Converter) HVDC systems, particularly when used with long-distance cables like those laid underwater, poses unique challenges due to the complexity, environment, and advanced technology involved. Below are some of the key maintenance challenges associated with VSC/MMC HVDC cables:

CONSIDERATIONS: VIABILITY & MAINTENANCE

1. Accessibility and Repair Difficulty

• Underwater Cable Challenges: Underwater cables, especially those spanning thousands of kilometers, are difficult and costly to access for repairs. Locating the exact point of failure or damage often requires specialized equipment like remotely operated vehicles (ROVs) or submersibles.
• Complex Repair Operations: Repairing a damaged section involves lifting the cable from the seabed, conducting repairs, and re-laying the cable, which can be extremely time-consuming and expensive.

2. Converter Station Maintenance

• High Complexity: VSC and MMC stations are more complex than traditional converter stations due to the use of advanced power electronics, which include numerous semiconductor switches, capacitors, and control systems. Maintaining these components requires specialized knowledge and skills.
• Thermal Management Issues: The converters generate significant heat, requiring sophisticated cooling systems. Maintenance of these cooling systems is critical to ensure the converters operate within safe temperature ranges, and failure can lead to overheating and system shutdowns.
• High-Sensitivity Components: The semiconductors used in VSC and MMC are sensitive to electrical, thermal, and environmental stresses. Regular inspection and monitoring are required to prevent premature failure.

3. Insulation and Dielectric Issues

• Insulation Degradation: Over time, the insulation of HVDC cables can degrade due to electrical stress, thermal cycling, and exposure to environmental factors, leading to potential faults. Detecting and diagnosing insulation degradation in underwater or buried cables is particularly challenging.
• Partial Discharges: VSC/MMC systems are susceptible to partial discharges, especially under high voltage and thermal stress conditions, which can degrade insulation and cause eventual failure. Detecting these discharges early is crucial to prevent catastrophic damage.

4. Monitoring and Diagnostic Challenges

• Complex Monitoring Systems: VSC and MMC HVDC systems rely on advanced monitoring systems that continuously track voltage, current, temperature, and other critical parameters. Maintaining and calibrating these monitoring systems is essential to ensure they provide accurate data for preventive maintenance.
• Fault Detection and Localization: Identifying faults within a VSC/MMC HVDC system can be complex due to the multiple components and interconnected systems. Locating faults in long submarine cables requires sophisticated diagnostic tools like time-domain reflectometry, which can be difficult to deploy in remote locations.

5. Environmental and Corrosion Issues

• Marine Environment: Underwater cables are exposed to harsh marine conditions, including strong currents, saltwater corrosion, and biological fouling (marine organisms attaching to the cable). These conditions can degrade the outer sheath and armoring, leading to water ingress and electrical faults.
• Mechanical Damage: Cables are at risk of damage from fishing activities, anchoring, and underwater seismic events. Protective measures like burial in the seabed can reduce risk, but maintenance access becomes more challenging.

6. Converter Control System Maintenance

• Software and Firmware Updates: VSC and MMC systems rely on sophisticated control algorithms that require regular software and firmware updates to maintain performance, improve efficiency, and address cybersecurity vulnerabilities.
• System Calibration: Regular calibration of control systems is necessary to maintain precise voltage and frequency control, especially in complex multi-terminal HVDC networks.

7. Safety and Operational Downtime

• High Voltage Safety: Working on HVDC systems, especially those with VSC/MMC technology, requires strict safety protocols due to the high voltages involved. Maintenance personnel must be specially trained to handle the unique safety challenges posed by these systems.
• Downtime Impact: Scheduled maintenance and unexpected failures can lead to significant downtime, impacting power supply stability, especially when HVDC systems connect critical renewable energy sources to the grid.

8. Supply Chain and Spare Parts Availability

• Specialized Components: VSC and MMC systems use specialized components, such as high-power semiconductors and custom cooling systems, which may have long lead times for replacement parts. Ensuring a reliable supply chain for spare parts is crucial for minimizing downtime during maintenance.

Conclusion:

Maintaining VSC/MMC HVDC systems, especially when used with underwater cables, is challenging due to the complexity, environmental conditions, and critical nature of these components. Addressing these challenges requires advanced monitoring, specialized training, and robust preventive maintenance strategies to ensure reliable operation and minimize the risk of failures.

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