ABB REJ525 B412BAA Protection Relay

Technical Overview

The ABB REJ525 (REJ525 B412BAA) is a microprocessor-based secondary protection relay designed for comprehensive overcurrent and earth-fault detection. Though classified as a legacy component (inactive since 2011), it remains a vital asset for maintaining the selective protection of feeders, motors, and transformers in existing power distribution networks. 

Technical Specifications

The REJ525 B412BAA is defined by the following electrical and functional parameters:

• Protection Type: Non-directional three-phase overcurrent and non-directional earth-fault.

• Overcurrent Unit: Includes Low-set ($I>$) and High-set ($I>>$) stages.

• Earth-Fault Unit: Includes Low-set ($I_0>$) and High-set ($I_0>>$) stages.

• Time Characteristics: Selectable Definite Time or Inverse Definite Minimum Time (IDMT) curves.

• Output Matrix: Fully configurable contact matrix for routing start/trip signals to specific outputs.

• Control Logic: Integrated Circuit Breaker Failure Protection (CBFP).

• Monitoring Interface: HMI with alphanumeric LCD and manual maneuvering buttons.

• Self-Supervision: Continuous internal monitoring of hardware and software integrity.

• Disturbance Recording: Built-in fault data recorder for post-event analysis.

• Secondary Current Input: Standard current transformer (CT) measurement input.

Model Breakdown and Core Functionality

The ABB REJ525 B412BAA features a modular protection architecture that allows independent operation of each sensing unit:

• Overcurrent Stages: The high-set stage can be configured to provide instantaneous protection or a short delay. If set at the lower end of its range, the relay creates two nearly identical stages, making it suitable for two-stage load shedding applications.

• Earth-Fault Protection: The non-directional stages monitor neutral current to detect insulation failure or ground faults, supporting both conventional and high-sensitivity settings.

• Flexible Signal Routing: An output contact matrix allows engineers to customize which protection stage triggers specific alarms or circuit breaker operations, adapting to varied substation architectures.