Product Overview

The REX521 is a high-performance numerical feeder protection relay engineered for the comprehensive protection, control, and monitoring of medium-voltage distribution networks. Designed by ABB, the REX521 integrates advanced microprocessor technology to provide rapid fault detection and isolation, effectively safeguarding transformers, motors, and distribution feeders. Its modular hardware architecture and flexible software configuration allow it to adapt to diverse utility and industrial power system requirements. By combining multi-function protection logic with real-time measurement and disturbance recording, the REX521 ensures high system integrity and minimizes operational downtime in critical infrastructure.

Detailed Technical Specifications

• Manufacturer: ABB

• Model Designation: REX521

• Device Type: Numerical Feeder Protection Relay

• Protection Logic: Non-directional/directional overcurrent, earth-fault, thermal overload, and phase imbalance protection

• Rated Current Input: 1 A or 5 A (Selectable via hardware/software)

• Rated Voltage Input: Standard 100 V / 110 V AC

• Nominal Frequency: 50 / 60 Hz

• Auxiliary Power Supply: 24–250 V DC or 48–240 V AC (Wide-range universal input)

• Digital I/O: Multiple programmable binary inputs and outputs for interlocking and signaling

• Communication Protocols: Modbus RTU/TCP, IEC 60870-5-103, and SPA bus

• Monitoring & Recording: Integrated disturbance recorder and comprehensive event logs (up to 200 events)

• Interface: Front-panel LCD display with dedicated navigation push buttons

• Operating Temperature: -25°C to +70°C

• Dimensions (WxHxD): 160 mm x 180 mm x 200 mm

• Weight: 2.5 kg

• Mounting Configuration: Flush panel-mounted unit

• Ingress Protection: IP20 (Rear), Front panel varies by installation (up to IP54 with protective cover)

• Compliance: IEC 60255 series for protection relays