Relay Protection Codes and Prices

Relay protection codes are standardized ANSI/IEEE device numbers that identify the function of protective relays, with prices varying from a few hundred to several thousand dollars depending on type and features.

ANSI/IEEE Relay Protection Codes

ANSI device numbers are used to identify the function of protective relays in electrical power systems. Each number corresponds to a specific protective function, and letters can be added as suffixes or prefixes to indicate special applications or connections ( ). Common examples include:

• 50 – Instantaneous overcurrent relay
• 51 – Time overcurrent relay
• 27 – Undervoltage relay
• 59 – Overvoltage relay
• 87T – Transformer differential relay
• 51G / 59G – Ground overcurrent or overvoltage relay
• 11 – Multifunction device performing multiple protective functions Suffixes like N indicate neutral connection (e.g., 59N), while G denotes ground protection ( ). Multifunction relays combine several device numbers, such as a 27/59 relay, which provides both under- and overvoltage protection ( ). ANSI codes are widely used in documentation, single-line diagrams, and schematics, even in regions where IEC standards predominate. IEC uses graphical symbols, but ANSI numbers remain common for clarity and standardization ( ).

Directional Overcurrent Protection

Directional overcurrent relays require both current and voltage inputs to determine the fault direction. Unlike non-directional overcurrent relays, which trip when current exceeds a set value, directional relays trip only if the fault occurs in the predefined direction, providing selective protection for complex networks ( ).

Relay Prices

Relay prices vary depending on type, voltage rating, and functionality:

• Basic electromechanical relays: $100–$500
• Digital or microprocessor-based relays: $500–$2,500
• Multifunction relays (e.g., 7–10 functions in one device): $1,500–$5,000
• High-end protection relays for transformers, generators, or transmission lines: $3,000–$10,000+ Prices are influenced by manufacturer, features (communication protocols, metering, event recording), and compliance with standards. Leading brands include ABB, Siemens, Schneider Electric, and SEL.

Summary

ANSI/IEEE relay codes provide a standardized method to identify protective functions, while relay prices depend on technology, complexity, and application. Understanding both the codes and the cost helps in selecting the right relay for system protection and budgeting.