Siemens SIPROTEC Compact 7SJ81 Feeder & Overcurrent Protection Relay

The Siemens SIPROTEC Compact 7SJ81 is a specialized feeder and overcurrent protection relay designed for applications using LPIT (Low Power Instrument Transformers), including low-power current transformers and voltage sensors. It is part of the SIPROTEC Compact series, offering reliable protection in a compact and cost-effective design.

The relay is optimized for modern digital substations and sensor-based measurement systems, where conventional CT/VT inputs are replaced by low-power sensors. It provides accurate measurement and protection performance while supporting advanced communication and integration features.

With its predefined hardware configuration and simplified engineering, the 7SJ81 ensures quick installation, easy commissioning, and seamless integration into IEC 61850-based automation systems. It is ideal for feeder protection in both utility and industrial environments adopting digital substation technologies.

Main Function

• Feeder Protection
• Overcurrent Protection (LPIT-based systems)

Tripping

• 3-pole tripping
• Fast and selective fault isolation

Technical Specifications

Protection & Functional Features

• Feeder protection for:
  • Radial networks
  • Distribution feeders
• Overcurrent protection:
  • Instantaneous and time-delayed
• Detects:
  • Phase faults
  • Earth faults
• Designed specifically for:
  • LPIT (Low Power Instrument Transformers)
  • Low-power current and voltage sensors
• Ensures:
  • Accurate measurement with sensor inputs
  • Reliable operation in digital substations

Hardware & Compact Design

• Compact, fixed hardware design (non-modular)
• Predefined configuration for LPIT applications
• Sensor-based inputs instead of conventional CT/VT
• Typical configuration:
  • LPIT current/voltage inputs
  • Binary inputs: ~11
  • Binary outputs: ~9
• Space-saving and cost-effective solution

Communication & Protocols

• IEC 61850 Edition 2 compliant
• GOOSE messaging support
• Supports:
  • Process bus (Sampled Values)
  • Modbus TCP
• Ideal for fully digital substations

Engineering & Software

• Configurable via DIGSI 5
• Simplified parameterization and commissioning
• Predefined templates for feeder applications

Advanced Features

• Designed for sensor-based digital substations
• Supports Sampled Values (SV) for process bus applications
• Reliable SIPROTEC platform performance
• Basic monitoring and diagnostics

Applications

• Feeder protection in digital substations
• LPIT-based systems (low-power CT/VT)
• Utility distribution networks
• Industrial power systems
• Smart grid and automation systems