Siemens SIPROTEC 5 7UT87 Transformer Differential Protection Relay

The Siemens SIPROTEC 5 7UT87 is a high-end modular transformer differential protection relay designed for multi-winding transformers with up to 5 windings (sides). Built on the advanced SIPROTEC 5 platform, it provides fast, selective, and highly reliable protection for complex transformer configurations used in modern power systems.

This relay acts as the main protection for multi-winding transformers, offering precise differential protection using advanced algorithms that ensure high sensitivity for internal faults while maintaining stability during inrush currents, overexcitation, and current transformer saturation. It is ideal for protecting complex transformer arrangements, including autotransformers, phase-shifting transformers, and converter transformers.

With its modular and scalable hardware architecture, the 7UT87 allows flexible I/O configuration based on project requirements. It integrates protection, control, automation, monitoring, and power quality functions into a single device, making it a future-ready solution for digital substations.

Engineered using DIGSI 5 and supporting IEC 61850 communication, the relay enables seamless integration, advanced automation, and high cybersecurity standards, ensuring long-term reliability and operational efficiency.

Main Function

• Transformer Differential Protection (up to 5 windings)

Tripping

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

Technical Specifications

Protection & Functional Features

• Differential protection for multi-winding transformers (up to 5 sides)
• Suitable for:
  • Power transformers
  • Auto-transformers
  • Phase-shifting transformers
  • Converter transformers (HVDC applications)
• Advanced protection algorithms ensure:
  • High sensitivity for internal faults
  • Stability during CT saturation
  • Secure operation during inrush and overexcitation conditions
• Supports:
  • Restricted earth fault protection
  • Overcurrent and backup protection functions
• Detects:
  • Phase faults
  • Earth faults

Hardware & Modular Design

• Fully modular and expandable I/O configuration
• Supports multiple measuring points for complex transformer systems
• Typical configurations:
  • High number of CT inputs (for multi-winding transformers)
  • Flexible VT inputs depending on application
  • Scalable binary inputs and outputs
• Available in multiple housing sizes (½ × 19″ to full rack)
• Conformal coating for harsh environmental conditions
• Scalable design for future expansion

Communication & Protocols

• IEC 61850 Edition 1 / 2 / 2.1 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 

• Web-based user interface for remote monitoring
• Advanced cybersecurity:
  • Role-based access control (RBAC)
  • Digitally signed firmware
  • Secure network authentication (IEEE 802.1X)
• Digital Twin support for simulation and testing
• Process bus ready (Sampled Values support)
• Power Quality monitoring (PQ Basic)
• PMU (Phasor Measurement Unit) functionality

Applications

• Protection of multi-winding transformers (up to 5 windings)
• Utility substations (HV/EHV)
• Industrial power systems
• Complex transformer configurations:
  • HVDC converter stations
  • Phase-shifting transformers
  • Large power transformers
• Protection of transformers connected to:
  • Lines
  • Cables
  • Reactors