TRANSFORMATOR RECTIFIER UNITS
A DC Power equipment such as Transformer Rectifier supplies current that is applied for Cathodic Protection of buried or immersed metal structure. The Transformer Rectifiers (TR) are normally used on impressed cathodic protection designs.
Definitions
- TR (Transformer Rectifier): A power source with a rectifier that converts alternating current (AC) from a power source into direct current (DC). Available in variants with RF/IP protection.
- Impressed Cathodic Protection (ICP): A corrosion mitigation method that uses a controlled, continuous DC current to drive the metal surface toward a desired potential via sacrificial or impressed anodes.
- Anode: The electrode (e.g., graphite, zinc, or other semi-passive materials) that provides a constant, controlled current to the protected structure.
- Enclosure/Static Circuit: The mechanical and electrical infrastructure that houses the TR, control panel, and interconnecting wiring.
How It Works
- The TR draws power from an AC source.
- Internal rectification converts AC to DC.
- The DC output is applied to the protected structure through anodes, establishing a protective potential.
- Load and soil resistivity influence the protection effectiveness.
- The control cabinet allows setting of current/voltage and safety interlocks as needed.
System Components
- Input Protection and Power Module (TR): AC input, conversion, and rectification.
- DC Output Control Module: Current/voltage regulation, current limiting, overcurrent protection.
- Control Panel: Setting values, monitoring, alarms, and logging.
- Reference Electrode and Anode System: Reference electrodes and protection anodes for surface potential control.
- Interconnection Hardware: Junction boxes, conductors, and grounding equipment.
- Environmental Protection: IP rating appropriate for immersion/soil, and thermal management.
Design and Selection Criteria
- Operating Voltage and Current Capacity: Ability to deliver required DC current and voltage for protection.
- Safety and Protection Features: Overcurrent, short-circuit protection, phase/line monitoring, fault indicators.
- DC Output Monitoring: Remote monitoring capabilities, profiles, and event logging.
- Environmental Conditions: IP rating, ingress protection, and corrosion resistance.
- Compliance and Standards: Alignment with IEC, IEEE, NACE, and region-specific requirements.
- Maintenance and Reliability: Accessibility, modular design, and ease of redundancy/configuration.
Functional Features
- Continuous or programmable DC current profiles.
- Current limiting and emergency interlock functions.
- Remote monitoring of potential, current, voltage, and alarms.
- Integration with SCADA/EMS/OMS systems via protocols such as Modbus and DNP3.
- Safety and Maintenance
- Key safety practices:
- Do not work live; apply lockout/tagout.
- Verify insulation integrity.
- Measure grounding resistance and ensure proper grounding.
- Regular inspection of cabling and connections.
- Maintenance activities:
- Monthly basic checks (input voltage, output current, alarm status).
- Annual comprehensive maintenance (rectifier health, cooling system, service life assessment).
Frequently Asked Questions (FAQ)
- What happens if the TR output current is lost?
- Protection effectiveness decreases; verify target potential and adjust settings accordingly.
- Which standards should be followed?
- Depends on project and region. Common interfaces include IEC/Modbus for remote communication; IEC 62304 may be relevant for safety decisions; regional standards such as NACE SP0169 for corrosion mitigation are often important.
- Where should maintenance records be stored?
- In SCADA/EMS software or a centralized maintenance log system.
