Siemens SIPROTEC 5 7UT85 Transformer Differential Protection Relay

The Siemens SIPROTEC 5 7UT85 is a high-performance modular transformer differential protection relay designed specifically for 2-winding transformers. Built on the advanced SIPROTEC 5 platform, it provides fast, selective, and highly reliable protection to ensure maximum safety and operational stability of power transformers.

The relay serves as the main protection for transformers, offering precise differential protection using advanced algorithms. In addition to primary protection, it also supports multiple backup protection functions for connected equipment such as cables, lines, and reactors.

With its modular and expandable hardware architecture, the 7UT85 allows flexible configuration tailored to project requirements. It integrates protection, control, automation, monitoring, and power quality functions into a single device, making it ideal for modern digital substations.

Engineered with DIGSI 5 and supporting IEC 61850 Edition 2, the relay enables seamless communication, advanced automation, and future-ready grid integration. Its robust design, advanced cybersecurity, and scalable architecture ensure long-term reliability and reduced operational costs.

Main Function

• Transformer Differential Protection (2-winding transformers)

Tripping

• 3-pole tripping
• High-speed fault detection and isolation

Technical Specifications

Protection & Functional Features

• Differential protection for 2-winding transformers
• Advanced algorithms ensure:
  • High sensitivity for internal faults
  • Stability during CT saturation
  • Secure operation during inrush and overexcitation
• Provides backup protection for:
  • Cables
  • Lines
  • Reactors
• Detects:
  • Phase faults
  • Earth faults
• Supports multiple protection and monitoring functions

Hardware & Modular Design

• Fully modular and expandable I/O configuration
• Flexible hardware architecture for customized applications
• Supports multiple measuring points (up to ~5, depending on configuration)
• Scalable design for future expansion
• Robust and reliable construction for substation environments

Communication & Protocols

• IEC 61850 Edition 2 compliant
• GOOSE messaging for high-speed communication
• Supports:
  • PRP / HSR redundancy
  • Modbus TCP, DNP3
• Enables seamless integration into digital substations

Engineering & Software

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

Advanced / Latest Features (2024–2026 Update)

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

Applications

• Protection of 2-winding power transformers
• Utility substations
• Industrial power systems
• Protection of transformers connected to:
  • Lines
  • Cables
  • Reactors