Siemens SIPROTEC 5 7UT86 Transformer & Reactor Differential Protection Relay

The Siemens SIPROTEC 5 7UT86 is a high-performance modular transformer differential protection relay designed for 3-winding transformers and reactors. Built on the advanced SIPROTEC 5 platform, it provides fast, selective, and highly reliable protection to ensure maximum safety and operational stability of critical power system assets.

This relay serves as the main protection for three-winding transformers, offering precise differential protection using advanced algorithms that ensure high sensitivity for internal faults while maintaining stability during inrush currents and CT saturation. However, It also includes additional protection and monitoring functions that can act as backup protection for connected equipment, such as cables, lines, and shunt reactors.

Therefore, with its modular and expandable hardware architecture, the 7UT86 allows flexible configuration tailored to project requirements. Moreover, engineered using DIGSI 5 and supporting IEC 61850 communication, Thus,  the relay integrates seamlessly into modern digital substations, providing a future-ready and scalable protection solution.

Main Function

• Transformer & Reactor Differential Protection (3-winding transformers)

Tripping

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

Technical Specifications

Protection & Functional Features

• Differential protection for 3-winding transformers (3 sides)
• Additionally, Expandable to support additional transformer configurations
• Advanced algorithms ensure:
  • High sensitivity for internal faults
  • Stability during CT saturation
  • Secure operation during inrush and overexcitation conditions
• Provides backup protection for:
  • Cables
  • Lines
  • Shunt reactors
• Supports:
  • Restricted earth fault protection
  • Multiple differential protection functions
• Detects:
  • Phase faults
  • Earth faults

Hardware & Modular Design

• Fully modular and expandable I/O configuration
• In addition, Typical configurations (as per standard variants):
  • Up to 12 current transformer inputs
  • Up to 4 voltage transformer inputs
  • Binary inputs: ~11 to 23
  • Binary outputs: ~18 to 34
• Flexible I/O scaling within SIPROTEC 5 platform
• As a result, Available in different housing sizes (½ × 19″ to full rack)
• However, Conformal coating for harsh environmental conditions

Communication & Protocols

• IEC 61850 Edition 1 / 2 / 2.1 compliant
• Meanwhile, GOOSE messaging for high-speed communication
• Supports:
  • PRP / HSR redundancy
  • Modbus TCP, DNP3
• Enables seamless integration into digital substations

Engineering & Software

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

Advanced / Latest Features (2024–2026 Update)

• As well as, a Web-based user interface for remote monitoring
• Advanced cybersecurity:
  • Role-based access control (RBAC)
  • Digitally signed Embedded software
  • Secure network authentication (IEEE 802.1X)
• Digital Twin support for simulation and testing
• Process bus ready (Sampled Values support)
• Power Quality (PQ Basic) monitoring support

Applications

• Also, Protection of 3-winding power transformers
• Auto-transformers and special transformers
• Protection of:
  • Reactors
  • Short lines and cables
• Utility substations
• Industrial power systems
• Complex transformer applications such as:
  • Phase shifters
  • HVDC and converter transformers