International Code for Relay Protection

International relay protection function codes are standardized identifiers, primarily ANSI/IEEE device numbers, used to denote specific protective relay functions in electrical power systems. Overview of ANSI/IEEE Device NumbersANSI/IEEE device numbers are defined in Standard C37. 2 and are widely used to identify the functions of protective relays, circuit breakers, and other control devices in power systems.

Each number corresponds to a specific protective function, such as overcurrent, differential protection, or voltage monitoring. Historically, each device performed a single function, but modern microprocessor-based relays can perform multiple functions, often denoted as "Multifunction Devices" (device 11) while still referencing individual function numbers in schematics.

Common ANS

I Device Numbers50/51 – Instantaneous/Time Overcurrent Relay50N/51N – Neutral Overcurrent Relay27 – Undervoltage Relay59 – Overvoltage Relay59N – Neutral Overvoltage Relay87 – Differential Protection (87T for transformers, 87G for generators)46 – Negative Sequence Overcurrent (phase unbalance protection)79 – Reclosing Relay86 – Lockout Relay Suffixes are used to indicate specific conditions or connections, such as G for ground, N for neutral, or T for transformer-specific protection.

IEC Standards and Symbols

The IE

C 60617 and IEC 617 standards provide graphical symbols and terminology for relay functions, which differ from the ANSI numbering system.

IE

C symbols are often used in international documentation and can be mapped to ANSI numbers for cross-reference. For example, an ANSI 50/51 overcurrent relay corresponds to an IEC overcurrent symbol with a time-delay indication.

Application in Protection Systems

Relay function codes are used in: Single-line diagrams to indicate the type of protection applied to each circuit or equipmentRelay settings and coordination studies to ensure proper operation during faultsDocumentation and maintenance to identify relay functions and their operational logic Modern relays may combine multiple ANSI functions in one device, but the function codes remain essential for clarity in design, operation, and troubleshooting.

Summary

International relay protection function codes provide a standardized method to identify and communicate relay functions across different systems and regions. ANSI/IEEE device numbers are widely used in North America, while IEC symbols are common internationally. Understanding both systems and their mappings is crucial for protection engineers to design, operate, and maintain reliable electrical power systems.