Case Study of Rockwill 72.5kV Dead Tank Circuit Breaker Project in South Africa

1.1 Project Background

South Africa, as the most industrialized country in Africa with the most developed power grid system, has stringent requirements for the reliability, breaking capacity, and environmental adaptability of high-voltage switchgear in its mines, metallurgy, energy sectors, and regional grid hubs. This project was implemented in a key industrial grid upgrade project in South Africa. The project site features high load density, high short-circuit capacity, and harsh environmental conditions, including high temperatures, intense solar radiation, and frequent dust. The original switchgear suffered from insufficient breaking margin, weak environmental resistance, and poor mechanical stability, which often led to power supply interruptions and abnormal protection operations, directly impacting industrial production continuity and grid safety.

To meet the objectives of safe and reliable grid operation and enhanced power supply security, the client selected Rockwill 72.5kV Dead Tank Circuit Breakers (DTCB). Leveraging Rockwill's mature design and manufacturing experience in high-voltage equipment, this project provides a high-reliability, high-performance high-voltage switching solution for the South African grid, ensuring grid stability and supporting the reliable integration of industrial and renewable energy loads.

1.2 Core Product & Technical Parameters

A total of 20 units of 72.5kV Dead Tank Circuit Breakers, along with their operating mechanisms and spare parts, were configured for this project. The core parameters are as follows:

Item

Technical Details

Product Name

72.5kV Dead Tank Circuit Breaker (DTCB)

Model

RHD-72.5-4000/40

Rated Maximum Voltage

72.5 kV

Rated Frequency

50/60 Hz

Rated Current

4000 A

Rated Short-circuit Breaking Current

40 kA

Rated Short-time Withstand Current

40 kA / 4 s

1-min Power Frequency Withstand Voltage

185 kV

Lightning Impulse Withstand Voltage (BIL)

450 kV

Rated SF₆ Gas Pressure (at 20°C, Gauge)

0.5 MPa

Annual SF₆ Leakage Rate

≤ 0.5%

SF₆ Gas Moisture Content

≤ 150 ppm(v)

Creepage Distance

25-31 mm/kV

Control Circuit Voltage

DC 110 / 220 / 230 V

Supply Quantity

20 Units

Location

South Africa Industrial Grid Substations

Commissioning Year

2024

02 Manufacturing & Quality Assurance 2.1 Core Technical Design

The Rockwill RHD-72.5-4000/40 Dead Tank Circuit Breaker features a fully enclosed dead tank structure. The arc-extinguishing chamber and the main conductive circuit are sealed within the SF₆ gas tank, effectively resisting the effects of high temperature, dust, and humidity in South Africa, providing significantly better operational stability than live tank (open-type) equipment.

• High Performance:Utilizing mature self-blast arc-extinguishing principles, with a 40 kA short-circuit breaking capacity and 4000 A rated current, it meets the demands of frequent operation under high-load and high-short-circuit-capacity conditions.
• Structural Integrity:The tank is made of high-strength steel with excellent anti-corrosion and anti-rust properties, ensuring structural rigidity for long-distance transport and long-term outdoor operation.
• Dead Tank Advantage:The structure features a low center of gravity and superior seismic performance. With built-in Current Transformers (CTs), it is more suitable for the complex geological environments of South African mining areas compared to traditional live tank equipment.
• Reliable Mechanism:The spring operating mechanism is highly reliable and requires no external air or oil source, ensuring simple maintenance and high suitability for overseas O&M conditions.
• Enhanced Insulation:The creepage distance reaches 25-31 mm/kV, meeting the insulation requirements for high-altitude and heavily polluted areas in South Africa. The annual SF₆ leakage rate is ≤5%, significantly reducing the frequency of gas refilling.

2.2 Quality Certification

Rockwill strictly implements ISO 9001 (Quality), ISO 14001 (Environment), and ISO 45001 (Occupational Health & Safety) management systems. All products have passed type tests and factory acceptance tests in authoritative laboratories, complying with IEC 62271-100 international standards and South African grid technical specifications.

03 Factory Acceptance Testing (FAT)

All 20 units completed full-item factory acceptance tests in accordance with IEC standards:

• Dielectric Withstand Test:1-min power frequency withstand (185 kV) and lightning impulse withstand (450 kV) tests passed without breakdown or flashover.
• Short-circuit Breaking Test:Reliable breaking verified at 40 kA. No restrike or abnormal erosion occurred. Temperature rise and mechanical performance were fully compliant during the 4 s short-time withstand period.
• Mechanical Operation Test:Thousands of opening/closing operations were performed, ensuring synchronization, bounce, and timing characteristics met design requirements.
• SF₆ Sealing Test:Measured annual leakage rate ≤ 0.5%, far superior to standard limits, ensuring long-term operation without frequent refilling.
• SF₆ Moisture Test:Moisture content ≤ 150 ppm(v), ensuring stable insulation and arc-extinguishing performance.
• Main Circuit Resistance Test:Resistance values were compliant, ensuring the 4000 A circuit operates without overheating.

04 Packaging & Shipping

The equipment utilized a specialized export packaging solution. The tank was secured in reinforced wooden crates with internal shock-absorbing materials and moisture-proof sealing. This design protects against sea transport and long-distance inland logistics in South Africa. All components and technical documentation were clearly labeled to ensure intact arrival and timely delivery.

05 Installation & Operation Summary 5.1 Installation Implementation

Rockwill's professional technical team provided on-site support in South Africa:

• Guided foundation acceptance and earthing system inspection.
• Supervised lifting, positioning, alignment, and securing of DTCB units.
• Completed SF₆ gas filling, leak detection, and moisture testing (0.5 MPa at 20°C).
• Performed secondary wiring, insulation testing, and opening/closing commissioning.
• Coordinated protection and control system commissioning to verify logic and interlocking.
• Conducted operation, inspection, and maintenance training for local personnel.

5.2 Operation Feedback

Since commissioning, the 20 units of RHD-72.5-4000/40 have operated stably without failure or abnormal alarms:

• Environmental Adaptation: The fully enclosed structure perfectly adapts to high temperatures, dust, and heavy pollution, providing high reliability in outdoor operations.
• Load Capacity: The 4000 A rated current meets high-power supply needs with excellent temperature rise control.
• Fault Protection: 40 kA breaking capacity and 100 kA peak withstand current provide reliable fault isolation for the grid.
• Superior Insulation: 185 kV power frequency and 450 kV BIL withstand voltages fully meet the insulation requirements of the South African grid, offering excellent lightning protection.
• O&M Efficiency: The low leakage rate (≤ 0.5%) significantly reduces maintenance workload.
• Grid Stability: Power supply reliability has significantly improved, ensuring continuous operation of industrial loads and reducing production interruptions.

The project has received high recognition from the South African client and local power authorities, demonstrating Rockwill's technical strength and reliability in the high-end African grid market.

06 Lifecycle Operation & Maintenance Services

Rockwill provides full lifecycle O&M support for the project, covering installation, monitoring, regular inspection, status assessment, troubleshooting, spare parts supply, and technical training. Through standardized, closed-loop management, we ensure long-term safe operation, extend equipment life, and reduce the total cost of ownership (TCO) for South African industrial users.

Contact us for more details and customized solutions!