Project Background

Three high-efficiency rectifier transformer systems were deployed for an industrial electrolysis plant in the Democratic Republic of the Congo (DRC). Designed to power multiple electrolytic processes, these systems ensure reliable DC power delivery with precise voltage control, critical for maintaining consistent electrochemical operations in a demanding environment.

Key Specifications​

• ​​Transformer Rating​​: 700kVA, 15kV primary voltage.
• ​​DC Output​​: 0–56V adjustable voltage, 10kA DC current per unit.
• ​​Application​​: Electrolysis process.
• ​​Quantity​​: 3 complete systems (parallel operation capability).

Rectification & Voltage Control System

​​Rectification Method​​:

12-pulse thyristor (SCR) rectification​​: Achieved through dual 6-pulse bridge configurations with phase-shifted transformer windings (30° displacement), reducing input harmonic distortion and enhancing grid compatibility.

​​Voltage Adjustment​​:

• ​​Coarse Adjustment​​: On-load tap changer (OLTC) integrated into each transformer for ±10% stepwise voltage regulation.
• ​​Fine Adjustment​​: Thyristor phase-angle control enables continuous DC voltage tuning from 0% to 100% of Udn (rated output).
• ​​Full Range Control​​: Combined OLTC and SCR systems provide seamless 0–100% output adjustability, ideal for dynamic process requirements.

Key Features​

• Harmonic Mitigation​​: 12-pulse design limits total harmonic distortion (THD) to <10%, compliant with IEEE 519 standards.
• ​​Precision Control​​: Hybrid regulation ensures ±0.75% voltage stability under load fluctuations.
• ​​Robust Construction​​: Transformers feature Class H insulation and FOA (forced-oil-air) cooling to withstand DRC’s tropical climate (ambient temperatures up to 50°C).
• ​​Scalability​​: Parallel operation of three units allows flexible power distribution across multiple electrolytic lines.
• ​​Protection​​: Multi-tier safeguards include overcurrent, overtemperature, and arc-fault detection via PLC-based monitoring.

Operational Benefits​

1. ​​High Efficiency​​: System efficiency ≥97.5% at full load, minimizing energy waste.
2. ​​Process Adaptability​​: Real-time voltage adjustment accommodates varying electrolyte conditions and production demands.
3. ​​Redundancy​​: Three-unit configuration ensures uninterrupted operation; one unit can be maintained while others sustain production.
4. ​​Durability​​: Corrosion-resistant enclosures (IP54 rating) protect against dust and humidity prevalent in equatorial regions.

​​Conclusion​

This 12-pulse rectifier transformer system, combining OLTC and thyristor technologies, delivers a robust and scalable DC power solution for the DRC’s electrolysis industry. The three-unit installation enhances operational flexibility, redundancy, and process control, while the design prioritizes reliability in harsh environmental conditions. By integrating harmonic suppression, precision regulation, and climate resilience, the system meets both industrial performance standards and regional operational challenges.