ABB REL551 1MRK002480-AE｜Line differential protection terminal｜

Key Features
1. Flexible Hardware and Configuration
Open terminal architecture
Provides extensive configuration flexibility.
Supports expandable hardware options to satisfy different user application requirements.
Allows adaptation to various substation layouts and protection philosophies.
Four independent setting groups
Enables different protection parameter sets for changing operating conditions.
Typical applications:
Normal operation
Maintenance conditions
Seasonal network variations
Emergency operating modes
2. Protection Functions
Phase-Segregated Line Differential Protection

The REL 551 provides phase-segregated current differential protection, offering:

High sensitivity for internal line faults
Accurate phase fault identification
Selective tripping
Improved performance in complex network configurations

The differential protection compares current measurements at both ends of the protected line section and operates when the difference exceeds the defined threshold.

Advantages
Fast fault clearing
Excellent fault discrimination
Suitable for:
Overhead transmission lines
Underground cables
Parallel line applications
Networks with complicated fault current distribution
Phase and Residual Overcurrent Protection

Provides backup and supplementary protection through:

Phase Overcurrent Protection

Protects against:

Phase-to-phase faults
Three-phase short circuits
High current fault conditions
Residual Overcurrent Protection

Protects against:

Earth faults
Grounding system faults
Cable insulation failures
Thermal Overload Protection

Provides protection against excessive thermal stress caused by prolonged high current loading.

Applications include:

Cable thermal protection
Line loading supervision
Prevention of conductor overheating

The function calculates thermal effects based on current magnitude and operating time.

Additional Protection Function Library

An extended protection library is available, allowing users to add functions according to system requirements.

Possible functions include:

Distance protection
Earth-fault protection
Over/undervoltage protection
Frequency protection
Auto-reclosing functions
Synchronism checking
Breaker failure protection
Power system monitoring functions
3. Disturbance Recording and Analysis

The REL 551 includes an extensive disturbance reporting system.

Recording Capacity
10 latest disturbances stored
Up to 40 seconds disturbance recording duration

Recorded information may include:

Phase currents
Residual currents
Binary input/output signals
Protection operation signals
Trip commands
Internal logic states
Benefits
Fault investigation
Protection performance verification
System event analysis
Maintenance troubleshooting
4. Control and Monitoring Functions
Wide Range of Control Functions

The terminal supports various control operations, including:

Circuit breaker control
Disconnector control
Switching sequences
Interlocking logic
Local and remote operation
LED Indication System
18 programmable LEDs

Provides extensive local indication for:

Protection operation
Alarm conditions
Trip status
Communication status
User-defined signals
Local Human-Machine Interface (HMI)

The integrated HMI provides:

Local operation
Parameter setting
Measurement display
Alarm/event viewing
Protection status monitoring
5. Communication and Data Management
Dual Serial Communication

Supports:

Two simultaneous serial communication channels
Integration with substation automation systems

Possible communication applications:

SCADA connection
Remote engineering access
Protection coordination systems
Internal Event Recorder and Self-Supervision

The REL 551 provides extensive self-monitoring functions, including:

Hardware diagnostics
Software supervision
Communication monitoring
Internal fault detection

The internal event recorder captures:

Protection operations
Control commands
System alarms
Diagnostic information
6. Time Synchronization
High-Accuracy Time Synchronization
Resolution: 1 ms

Provides accurate event correlation between:

Multiple protection devices
Substation automation systems
Disturbance records

Typical synchronization sources:

IRIG-B
Communication-based time synchronization
External clock systems