Application Solution for TSTY Electrical Products in a Charging Station Project in Rwanda

Electric vehicle (EV) charging infrastructure in Rwanda is expanding rapidly. Charging stations for electric buses are already in operation in Kigali, and an intercity fast-charging corridor is extending toward the south. EV charging loads are characterized by high-impact surges, significant harmonic content, and stringent requirements for power supply continuity; these factors necessitate higher-than-standard capabilities for transformer overload capacity and protection coordination within switchgear. To address the requirements specified by a Rwandan client—namely 1250kVA package substations, 1000kVA oil-immersed transformers, and 30kV indoor switchgear—TSTY has developed the following tailored solution.

 1250kVA Box-Type Substation (30/0.4kV, Copper Windings)

Application: Serves as the primary power entry node for charging stations, integrating high-voltage power reception, voltage transformation, and low-voltage distribution and protection. This design minimizes on-site civil engineering and wiring requirements.

Configuration Highlights:

Rated Capacity: 1250 kVA, capable of handling the peak loads generated when multiple DC fast-charging piles operate simultaneously. The TSTY compact prefabricated substation series includes the 1250 kVA capacity rating.

Voltage Levels: 30 kV on the high-voltage side and 0.4 kV on the low-voltage side, aligned with the grid connection standards in Rwanda.

Winding Material: Copper. Copper conductors offer superior thermal stability under the fluctuating load conditions typical of charging stations; TSTY oil-immersed transformers with copper windings are designed for a service life of over 30 years.

Structural Design: European-style compact prefabricated substation. The enclosure features a 7-layer nanocomposite coating, providing over 20 years of corrosion resistance—well-suited for the high-humidity environment experienced during Rwanda’s rainy seasons. The ingress protection (IP) rating can be configured based on site-specific conditions to ensure suitability for outdoor installation.

Integrated Components: Includes a high-voltage ring main unit (RMU)/load-break switch, a 1250 kVA transformer, and a low-voltage distribution cabinet (incorporating feeder circuits for charging piles, as well as metering and protection units). The unit is fully prefabricated at the factory, requiring only foundation placement and cable connection upon arrival at the site.

 1000 kVA oil-immersed transformer (30/0.4 kV, copper windings)

Application: Serves as a secondary power source or a backup transformer for load expansion at charging stations. It complements existing 1250kVA package substations, thereby increasing power supply redundancy.

Key Specifications:

Rated Capacity: 1000kVA; three-phase, oil-immersed distribution transformer.

Voltage Configuration: 30kV / 0.4kV—matching the high-voltage side of the package substations to facilitate a unified high-voltage busbar configuration within the station.

Winding Material: Copper. TSTY oil-immersed transformers utilize high-permeability, grain-oriented silicon steel sheets (sourced from Baosteel/Wugang) and feature a multi-step, 45-degree mitered-joint core construction to minimize no-load losses and noise.

Insulation and Cooling: Manufactured using vacuum oil-filling and high-temperature drying processes. The insulating oil offers high thermal stability, well-suited to the daily load fluctuations typical of charging stations. The transformer tank possesses a mechanical strength of ≥345 MPa, ensuring durability during both transport and operation.

Compliance and Certification: Designed and tested in accordance with IEC standards. TSTY oil-immersed transformers have been exported to over 80 countries; factory test reports compliant with grid-connection requirements for Rwanda can be provided.

 30kV Indoor Switchgear

Application: Installed in the power distribution room of a charging station to serve as control and protection equipment for 30kV incoming lines, bus-tie connections, and transformer feeders.

Configuration Details:

Switchgear Type: Armored, withdrawable, metal-enclosed switchgear (e.g., KYN61-40.5 series). Rated for 40.5kV, it is fully compatible with 30kV systems. TSTY offers medium-voltage switchgear products for this voltage class.

Rated Parameters: Rated current is determined by transformer capacity (e.g., ~24A for 1250kVA @ 30kV, ~19A for 1000kVA); a 630A rating is sufficient. Short-circuit breaking capacity is calculated based on the system's short-circuit capacity—typically configured at 25kA or 31.5kA.

Insulation Level: For a 30kV system, the equipment meets the 40.5kV standard, featuring a power-frequency withstand voltage of 95kV and a lightning impulse withstand voltage of 185kV, providing an ample insulation margin.

Protection and Interlocking: The enclosure offers an IP4X protection rating, with IP2X protection between compartments. It includes "five-prevention" (five-fold safety) mechanical interlocks to ensure operational safety.

Installation: Designed for indoor use. Cable entry/exit (bottom-in/bottom-out or overhead) is determined by the specific layout of the power distribution room.

 Explanation of Solution Synergy

The high-voltage side for all three units is standardized at 30 kV, allowing for a single-bus or sectionalized bus configuration within the station, with the pad-mounted transformer and oil-immersed transformer serving as backups for each other. Both transformers utilize copper windings, ensuring consistent temperature-rise performance and expected service life, even in Rwanda’s hot and humid climate. The relay protection settings for the switchgear are coordinated with the load characteristics of the EV charging piles to prevent nuisance tripping during the start-up or shut-down of charging modules.

Delivery and Service: TSTY operates a 250,000 m² manufacturing facility with an annual production capacity of 30,000 pad-mounted transformers, supported by comprehensive production lines for oil-immersed transformers and switchgear. For the Rwanda project, we provide technical documentation in English, facilitate factory acceptance testing (FAT) witnessing, and offer remote installation guidance. Should you require further refinement of the primary circuit configuration or the coordination of protection settings, our technical team is available for direct consultation.