National Standard for Relay Protection Design

DL/T 317-2025 is the current national standard in China for relay protection design, emphasizing dualized configurations, intelligent substations, and standardized protection device modeling.OverviewT...

National Standard for Relay Protection Design

DL/T 317-2025 is the current national standard in China for relay protection design, emphasizing dualized configurations, intelligent substations, and standardized protection device modeling.

Overview

The DL/T 317-2025 "Standardized Design Specification for Relay Protection Equipment" was issued by the National Energy Administration on June 30, 2025, replacing the 2010 edition. It establishes technical principles and design criteria for relay protection devices and circuits in power grids of 220 kV and above, covering lines, transformers, high-voltage shunt reactors, busbars, and bus-coupler sections . The standard reflects the trend toward digital and intelligent substations, incorporating merging units, intelligent terminals, SV sampling, and GOOSE communication.

Key Features

1. Dualized Configuration The standard emphasizes complete independence of dual protection sets, including CT/PT secondary windings, DC power sources, tripping coils, and communication channels. This ensures that a single fault does not compromise protection, enhancing grid N-2 reliability. For example, line pilot protection uses dual fiber optic channels with independent power sources and interface equipment . 2. Intelligent Station Device Modeling DL/T 317-2025 specifies modeling requirements for intelligent devices:

  • GOOSE and SV inputs use GGIO logical nodes.
  • Tripping outputs use PTRC/RBRF nodes.
  • Instrument transformers are modeled per phase to ensure redundancy.
  • Dual ADs in merging units are configured with identical TCTR or TVTR instances. This provides a unified framework for IEC 61850 engineering implementation . 3. Bus Tie (Sectionalizing) Charging Overcurrent Protection A dedicated chapter requires independent charging overcurrent protection devices with two stages of overcurrent and one stage of zero-sequence overcurrent. This design improves operational safety by avoiding logical complexity in busbar protection during charging conditions . 4. Functional Requirements The standard ensures that relays are:
  • Reliable and discriminate between fault and non-fault conditions.
  • Sensitive to operate under actual system conditions.
  • Fast-operating to isolate faults promptly.
  • Supports various relay types: current, voltage, impedance, power, frequency, differential, directional, and distance relays .

Testing and Commissioning

DL/T 317-2025 aligns with practical testing procedures for switchgear, instrument transformers, and relays, ensuring that close, trip, indication, and alarm circuits function correctly. Dualized configurations allow maintenance on one set of protection without affecting the other .

International Alignment

While DL/T 317-2025 is a national standard, it complements IEC 60255-1:2022, which specifies common rules for measuring relays and protection equipment, and IEEE Std C37.90-2005, which defines service conditions, electrical ratings, and testing requirements for relays and relay systems . This ensures interoperability and adherence to global best practices.

Practical Implications

  • Enhances grid reliability and fault isolation.
  • Supports digital substation integration and IEC 61850 compliance.
  • Provides a clear framework for design, modeling, and testing of protection devices.
  • Ensures redundancy and operational safety through dualized configurations. DL/T 317-2025 represents a significant step in modernizing relay protection design, integrating intelligent systems, and standardizing protection practices for high-voltage power networks.
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