Siemens SIPROTEC Compact 7SK81 Motor & Generator Protection Relay

The Siemens SIPROTEC Compact 7SK81 is a specialized motor and generator protection relay designed for applications using LPIT (Low Power Instrument Transformers) such as low-power current 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 LPIT sensors. It provides accurate protection and monitoring for motors and small generators, ensuring safe and efficient operation.

With its predefined compact hardware configuration, the 7SK81 enables easy selection, quick installation, and simplified commissioning. It integrates seamlessly into IEC 61850-based systems, making it ideal for smart grids and advanced automation environments.

Main Function

• Motor Protection
• Generator Protection (Small Generators)

Tripping

• 3-pole tripping
• Fast and reliable fault isolation

Technical Specifications

Protection & Functional Features

• Protection for:
  • Motors (small to medium)
  • Small generators
• Protection functions include:
  • Thermal overload protection
  • Overcurrent protection
  • Earth fault protection
  • Negative sequence (unbalance) protection
  • Stall / locked rotor protection
• Detects:
  • Phase faults
  • Earth faults
• Designed specifically for:
  • LPIT (Low Power Instrument Transformers)
  • Sensor-based measurement systems

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 digital substations

Engineering & Software

• Configurable via DIGSI 5
• Simplified parameterization and commissioning
• Predefined templates for motor/generator applications

Advanced Features

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

Applications

• Motor protection in digital substations
• Generator protection (small generators)
• Industrial motor-driven systems
• LPIT / sensor-based power systems
• Smart grid and automation applications