16MVA 33 /6.6kV Compact Skid Substation Solution – Sodium Based Battery Energy Storage System (SBBESS)

ArmCoil delivers cutting-edge engineering excellence through its 16MVA 33/6.6kV compact skid-mounted substation—a high-performance solution developed for integration into a Sodium-Based Battery Energy Storage System (SBBESS).

ArmCoil Afrika was appointed to design, engineer, and manufacture a fully integrated substation solution to interface with a molten sodium battery system, where sodium acts as the active material for energy storage and release. The system enables controlled charge and discharge of energy into the medium voltage network.

The solution was developed to facilitate efficient step-down transformation and distribution of energy from the battery system, ensuring stable and reliable integration into the client’s electrical network.

This project required a compact, transportable, and fully integrated substation capable of delivering high performance, operational flexibility, and enhanced protection. ArmCoil’s scope included full design and engineering, manufacturing, integration of all electrical components, factory testing, and preparation for site installation.

The client required a high-capacity, turnkey substation solution capable of seamlessly integrating transformer, protection, and switchgear systems into a single skid-mounted platform, specifically designed for a Sodium-Based Battery Energy Storage System.

Key requirements included:

• Transformer Rating: 16MVA, 33/6.6kV, 3-phase, 50Hz
• Vector Group: YNd11
• Cooling System: ONAN (Oil Natural Air Natural)
• Auxiliary Transformer: 50kVA, 6.6/0.4kV Dyn11 (220V capable) mounted on skid
• Impedance: 8% with K-factor K-3 rating
• Application: Sodium-Based Battery Energy Storage System (SBBESS)
• Load Profile: Designed for dynamic battery charge and discharge cycles
• On-Load Tap Changer (OLTC): MR VACUTAP VVS system for voltage regulation

Protection & Monitoring:

• SEL protection relays (including differential protection)
• Battery Trip Units (BTU)
• Arc-flash detection systems
• Neutral Earthing Resistor (NER):
• 33kV oil-cooled NER with full monitoring (NERPRO system)

Switchgear Integration:.

• 33kV and 6.6kV fully motorized switchgear with LV panels

Kiosk Solution:

• Stand-alone 33kV kiosk for network interfacing
• Safety Features:
• Surge arrestors on incomers
• Pressure relief devices and monitoring instrumentation

Standards Compliance:

• IEC 60076 and relevant SANS specifications

The complete solution was engineered to be compact, modular, and pre-assembled, enabling rapid deployment and minimal on-site installation time.

ArmCoil’s multidisciplinary engineering team developed a fully integrated skid-based solution that combines transformer, switchgear, and protection systems into a unified platform.

Innovation in Compact Design

• All major components—including transformer, MV/HV switchgear, NER, and auxiliary systems—are mounted onto a single engineered skid structure, minimizing footprint and simplifying installation.
• The system was specifically designed to support dynamic battery charge and discharge cycles, ensuring stable operation under continuously fluctuating load conditions typical of energy storage applications.

Advanced Protection Architecture

• The system incorporates SEL-based protection schemes, including line differential and feeder protection, ensuring rapid fault detection and isolation across both HV and MV networks.

Voltage Control & Stability

• The inclusion of an on-load tap changer (OLTC) enables real-time voltage regulation, maintaining network stability under variable load conditions.

Enhanced Monitoring Systems

• Integration of NERPRO and intelligent relay systems enables real-time monitoring of earth faults, system conditions, and operational performance.

Modular Expansion Capability

• A stand-alone 33kV kiosk provides flexibility for future network expansion and simplified grid interfacing.

The final design ensures full compliance with IEC standards while meeting the operational demands of advanced energy storage systems.

Manufacturing was carried out at ArmCoil’s Johannesburg facility under ISO-certified quality, environmental, and safety management systems.

Scope of manufacturing included:

• Fabrication of transformer tank, skid base, and structural steelwork
• Integration of HV and MV switchgear compartments
• Installation of OLTC, NER, and auxiliary transformer systems
• Full electrical wiring, control integration, and labeling
• Oil filling and processing under controlled conditions
• Installation of protection relays and communication systems

A comprehensive Factory Acceptance Test (FAT) programme was conducted, including:

• Insulation resistance and dielectric testing
• Functional testing of protection systems
• Verification of relay logic and interlocks
• Transformer routine testing in accordance with IEC 60076

High-voltage impulse testing was performed in accordance with SANS/IEC standards, confirming the transformer’s ability to withstand transient overvoltages and ensuring long-term reliability in service.

The completed 16MVA compact skid substation delivered:

• Reliable power transformation and distribution for solar generation integration
• Improved grid stability through OLTC voltage regulation
• Enhanced protection and fault response via advanced relay systems
• Reduced installation time through pre-assembled skid design
• Operational flexibility with integrated kiosk and modular configuration
• Compliance with international standards, ensuring long-term reliability

The successful execution of this project highlights ArmCoil’s capability to deliver large-scale, turnkey substation solutions tailored to modern energy infrastructure.

This project demonstrates ArmCoil’s ability to engineer and deliver high-capacity, fully integrated power solutions for demanding applications in the renewable energy sector.

By combining advanced protection systems, precision manufacturing, and innovative skid-mounted design, ArmCoil continues to set the benchmark for compact, efficient, and reliable substation solutions across Africa.