Siemens SIPROTEC 5 7SL87 Line Differential & Distance Protection Relay

The Siemens SIPROTEC 5 7SL87 is a high-end modular protection relay that combines line differential and distance protection in a single device. It is specifically designed for protecting overhead lines and cables across all voltage levels, including complex multi-terminal transmission networks.

Built on the advanced SIPROTEC 5 platform, the 7SL87 supports multi-end line protection (up to 6 line ends) and provides both single-pole and three-pole tripping, ensuring fast and selective fault isolation. Its adaptive differential protection algorithm ensures high sensitivity and stability even under challenging conditions such as current transformer saturation and capacitive charging currents.

With a minimum tripping time of ~9 ms, the relay delivers ultra-fast fault clearance, improving system reliability and reducing downtime. Its modular and scalable architecture allows flexible configuration, making it ideal for modern digital substations and future-ready grid infrastructures.

Main Function

• Line Differential Protection
• Distance Protection (main + backup protection)

Tripping

• 1-pole and 3-pole tripping
• Minimum tripping time: ~9 ms

Technical Specifications

Protection & Functional Features

• Combined line differential + distance protection
• Suitable for:
  • Overhead lines
  • Underground cables
• Supports multi-end protection (up to 6 line ends)
• Phase-selective protection for complex networks
• Adaptive differential algorithm ensures:
  • Stability during CT saturation
  • Immunity to transformer errors
  • Reliable operation during disturbances
• Distance protection functions:
  • Impedance-based protection
  • Reactance method (RMD)
  • Backup or secondary main protection
• Fault detection:
  • Phase faults
  • Ground faults

Hardware & Modular Design

• Fully modular and expandable I/O configuration
• 12 predefined standard variants available
• Typical configurations:
  • CT/VT: 4/4 or 8/8
  • Binary inputs: 5 to 31
  • Binary outputs: 8 to 46
• Flexible I/O scaling within SIPROTEC 5 platform
• Conformal coating for harsh environmental conditions
• Scalable design for future expansion

Communication & Protocols

• IEC 61850 Edition 2 compliant
• GOOSE messaging for high-speed communication
• Supports:
  • PRP / HSR redundancy
  • Modbus TCP, DNP3
  • Up to 4 communication modules
• Serial protection communication via:
  • Optical fiber
  • Two-wire connections
  • Communication networks
• Enables full digital substation integration

Engineering & Software

• Configurable via DIGSI 5 engineering tool
• Graphical logic configuration (CFC)
• Supports protection, control, automation, and monitoring
• Simplified commissioning, testing, and diagnostics

Advanced / Latest Features

• Web-based access for monitoring and diagnostics
• Advanced cybersecurity:
  • NERC CIP & BDEW compliant security features
  • Role-based access control
• Digital Twin support for simulation and testing
• Process bus ready (Sampled Values support)
• PMU (Phasor Measurement Unit) functionality
• Power Quality monitoring (PQ Basic)

Applications

• Transmission line protection (HV/EHV/MV)
• Multi-terminal line protection (up to 6 ends)
• Ring and mesh network protection
• Utility substations
• Industrial power systems
• Protection of lines with transformers or compensating coils in the protection zone