Siemens SIPROTEC 5 7SD87 Line Differential Protection Relay

The Siemens SIPROTEC 5 7SD87 is a high-end modular line differential protection relay designed for protecting overhead lines and cables in complex power networks. It is specifically engineered for multi-end line configurations (up to 6 line ends), making it ideal for advanced transmission systems such as ring, mesh, and multi-terminal networks.

Built on the powerful SIPROTEC 5 platform, the 7SD87 provides fast, selective, and reliable fault detection with both single-pole and three-pole tripping capabilities. Its adaptive differential protection algorithm ensures high sensitivity and stability even under challenging conditions such as current transformer saturation, transformer errors, and capacitive charging currents.

With its modular and scalable architecture, the relay integrates protection, control, automation, monitoring, and power quality functions into a single device. It is fully compatible with IEC 61850 Edition 2 and supports seamless integration into modern digital substations.

Main Function

• Line Differential Protection

Tripping

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

Technical Specifications

Protection & Functional Features

• Differential protection for:
  • Overhead lines
  • Underground cables
• Supports multi-end protection (up to 6 line ends)
• Phase-selective protection for complex networks
• Adaptive differential protection algorithm ensures:
  • Stability during CT saturation
  • Immunity to transformer errors
  • Reliable operation under network disturbances
• Supports:
  • Transformers and compensating coils within protection zone
• Fault detection:
  • Phase faults
  • Ground faults
• Supports PMU and power quality monitoring functions

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 environments
• Scalable 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 for redundancy and flexibility
• 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 and diagnostics

Advanced / Latest Features (2024–2026 Update)

• Web-based access for monitoring and diagnostics
• Advanced cybersecurity:
  • Role-based access control
  • Secure communication and firmware
• Digital Twin support for simulation and testing
• Process bus ready (Sampled Values support)
• High availability with redundant communication architecture

Applications

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