ABB REX 521 protective relay

ABB REX 521 protective relay

Product positioning and hardware configuration

REX 521 is a multifunctional protective relay that supports multiple hardware versions (Basic/Medium/High/Sensor) and standard configurations (such as B01/B02/M01/H01, etc.), suitable for different voltage levels and protection requirements.

Hardware differences:

Basic: Basic type, supports basic overcurrent and ground fault protection, with fewer digital inputs/outputs.

Medium: Enhanced, extended digital input/output, supports directional protection and automatic reclosing.

High/Sensor: A high-end model that integrates advanced functions such as sensor interfaces, voltage/frequency protection, and motor start monitoring.

Key components:

Built in current/voltage transformer interface, supporting 1A/5A current and 100V voltage input.

Provide digital input/output, communication ports (RS-232/RS-485), and optional fiber optic modules, supporting protocols such as Modbus and DNP 3.0.

Core functions and protective features

1. Protection function

Overcurrent protection:

Supports three-phase overcurrent (3I>, 3I>>, 3I>>>) and ground fault (Io>, Io>>, Io>>>), including directional (67N) and non directional configurations, supporting definite time (DT) and inverse time (IDMT) characteristics.

Built in harmonic suppression and excitation inrush current detection (3I2f>) to avoid misoperation.

Voltage and frequency protection:

Overvoltage/undervoltage protection (3U>, 3U<<), residual voltage protection (Uo>), frequency anomaly protection (f1/f2), supporting voltage imbalance and phase sequence protection (U1U2<>_1).

Motor and transformer protection:

Motor start-up monitoring (Is2t n<), thermal overload protection (3Ithdev>), phase sequence reversal protection (3I()), fuse fault detection (FUSEF).

Automatic reclosing (O ->I):

Supports up to 5 reclosures, can be triggered by protection start or trip signals, and has dead time and discrimination time settings.

2. Measurement and monitoring

Electrical quantity measurement:

Real time measurement of three-phase current/voltage, power, frequency, and energy, supporting true RMS and fundamental wave analysis.

The disturbance recorder (DREC) can capture fault waveforms and supports manual or triggered recording.

Status monitoring:

Circuit breaker wear monitoring (CB wear1), trip circuit supervision (TCS1), power input supervision (MCS 3I/3U).

Power quality monitoring (PQ 3Inf/PQ 3Unf), supporting harmonic analysis and THD/TDD calculations.

3. Communication and Control

Protocol support:

Standard SPA, Modbus RTU/ASCII, DNP 3.0, optional IEC 61850 adapter (requires expansion module).

Remote control:

Support local/remote switching (I<->O POS), circuit breaker opening and closing control (I<->O CB1), and integrated interlocking logic.

3、 Standard configuration and application scenarios

1. Basic Configuration (Basic: B01/B02)

Function: Non directional overcurrent/ground fault protection, thermal overload protection, B02 supports automatic reclosing.

Application: Single busbar system for outgoing or incoming line protection, suitable for resistance grounding or solid grounded networks.

2. Intermediate configuration (Medium: M01/M02)

Function: Add directional grounding fault protection (67N), phase sequence protection, M02 supports reclosing and angle control (BACTRL).

Application: Compensate for grounding or isolated networks, requiring selective protection for outgoing scenarios.