ABB REX521 Feeder Protection Relay | Medium Voltage Distribution

ABB REX521 Feeder Protection Relay – Intelligent Medium Voltage Distribution Safeguarding

The ABB REX521 is a versatile numerical feeder protection relay engineered for comprehensive protection, control, measurement, and supervision in medium voltage (MV) distribution networks. As part of ABB's proven Relion® protection relay family, the REX521 combines advanced protection algorithms with flexible communication capabilities to ensure reliable power distribution in utility substations, industrial facilities, and renewable energy installations.

Core Protection Functions

• Overcurrent Protection (50/51): Three-phase and ground overcurrent with definite-time and inverse-time characteristics (IEC/ANSI curves)
• Earth Fault Protection (50N/51N): Sensitive ground fault detection using residual current measurement
• Short-Circuit Protection: Instantaneous high-set overcurrent for rapid fault clearing
• Thermal Overload (49): Thermal replica modeling prevents conductor and equipment damage from sustained overloads
• Directional Protection: Optional directional overcurrent and earth fault elements for selective coordination
• Voltage Protection: Over/under voltage monitoring with adjustable time delays
• Frequency Protection: Over/under frequency detection for grid stability applications

Technical Specifications

• Current Inputs: Three-phase and residual current measurement (1A or 5A nominal)
• Voltage Inputs: Three-phase voltage monitoring (optional)
• Binary I/O: Up to 16 configurable binary inputs, 10 output relay contacts
• Communication: Rear RS-485 serial port (SPA, Modbus RTU), front USB for local configuration
• Optional Ethernet: IEC 61850, DNP3, Modbus TCP protocols available
• Power Supply: Wide-range 24-265 VAC/DC or 48-265 VDC options
• Operating Range: -25°C to +55°C ambient temperature
• Mounting: 19" rack (4U) or panel mount configuration
• Dimensions: 177 mm (H) × 177 mm (W) × 144 mm (D)
• Protection Rating: IP54 front panel, IP20 rear terminals
• Standards: IEC 60255, ANSI/IEEE C37.2, CE, UL, CSA certified

Application Scenarios & Industrial Solutions

Utility Distribution Networks: Deploy in primary and secondary substations to protect overhead lines and underground cable feeders serving residential, commercial, and industrial loads. The REX521's selective coordination capabilities minimize outage areas during fault conditions, improving system reliability and customer satisfaction indices (SAIDI/SAIFI).

Industrial Power Distribution: Ideal for manufacturing plants, refineries, and mining operations where critical process continuity depends on rapid fault isolation. Thermal overload protection prevents costly motor and transformer failures while maintaining production uptime.

Renewable Energy Integration: Protect feeders connecting solar farms, wind parks, and energy storage systems to utility grids. Directional protection elements enable bidirectional power flow management while maintaining compliance with IEEE 1547 interconnection standards.

Infrastructure & Transportation: Safeguard power distribution in airports, seaports, rail electrification systems, and data centers where high availability is mission-critical. The relay's extensive event recording facilitates rapid fault analysis and system restoration.

Advanced Measurement & Monitoring

• Real-Time Metering: Continuous measurement of current, voltage, power (active/reactive/apparent), power factor, and frequency
• Energy Metering: Accumulated energy consumption tracking for billing and load profiling
• Demand Monitoring: Peak demand recording with configurable integration periods
• Harmonic Analysis: Total harmonic distortion (THD) measurement for power quality assessment
• Event Recording: Time-stamped fault records with pre-fault and post-fault data capture
• Oscillography: High-resolution waveform recording for detailed fault analysis

Communication & Integration Capabilities

The REX521 supports multiple communication protocols enabling seamless integration with SCADA systems, substation automation platforms, and energy management systems. Standard Modbus RTU connectivity allows cost-effective integration with existing infrastructure, while optional IEC 61850 support provides future-proof compatibility with modern digital substations featuring GOOSE messaging and MMS reporting.

Related Feeder Protection & Control Products

Configuration & Commissioning

The REX521 is configured using ABB's PCM600 Protection and Control Manager software, providing an intuitive graphical interface for parameter setting, logic customization, and system testing. Built-in self-diagnostics continuously monitor relay health, while comprehensive test modes facilitate commissioning and periodic maintenance verification without service interruption.

Key Advantages for System Engineers

• ✓ Proven Reliability: Field-tested in thousands of installations worldwide with >99.9% availability
• ✓ Flexible Configuration: Adaptable protection schemes accommodate diverse network topologies
• ✓ Cost-Effective: Multi-functional design reduces panel space, wiring, and lifecycle costs
• ✓ Easy Integration: Standard protocols ensure compatibility with multi-vendor systems
• ✓ Future-Proof: Firmware upgradeable to support evolving grid requirements
• ✓ Global Support: ABB's worldwide service network provides rapid technical assistance

Compliance & Certifications

The REX521 meets international standards including IEC 60255 (measuring relays and protection equipment), ANSI/IEEE C37.2 (electrical power system device function numbers), and carries CE, UL, and CSA certifications for global deployment. EMC compliance ensures reliable operation in electrically noisy substation environments.

Ordering & Technical Support

• Model Number: REX521 (multiple configuration variants available)
• Availability: In-stock units ship within 3-5 business days
• Lead Time: Custom configurations available with 2-3 week lead time
• Warranty: Standard manufacturer warranty included
• Documentation: Complete technical manuals, application guides, and CAD drawings provided
• Training: On-site commissioning support and operator training available
• Spare Parts: Replacement modules and accessories stocked for rapid delivery

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