Relay protection device signal icons

Relay protection devices use standardized signal icons and symbols to represent their functions, types, and operational states in electrical schematics.

Overview of Relay Symbols

Relay protection devices are represented in schematics using graphical symbols (IEC 60617) or device numbers (ANSI/IEEE C37.2). These symbols indicate the type of relay, its function, and operational characteristics, allowing engineers to quickly interpret protection schemes .

• IEC Symbols (IEC 60617): Use standardized graphical icons to represent relays, coils, contacts, and auxiliary devices. Symbols are designed for clarity and international recognition, showing whether a relay is electromechanical, static, or has special features like LED indicators .
• ANSI/IEEE Device Numbers: Assign numbers to relay functions (e.g., 50 for instantaneous overcurrent, 51 for time-overcurrent). Letters may be added to indicate specific characteristics or auxiliary functions .

Common Relay Signal Icons

1. Relay Coil: Represented as a rectangle or oval with terminals; may include polarity dots for polarized relays or multiple windings for complex devices .
2. Contacts:
   • Make Contact (Normally Open): Shown as two lines that close when the relay is energized.
   • Break Contact (Normally Closed): Shown as two lines that open when the relay is energized.
   • Changeover Contact: Indicates switching between two circuits, sometimes with delayed operation symbols .
3. Static Relay Symbols: Include semiconductor contacts, LED actuators, or auxiliary power supply indicators .
4. Protection Function Indicators:
   • Overcurrent, earth fault, under/overvoltage, differential, and directional relays have specific symbols or device numbers.
   • Time-delay relays are often shown with a small clock or timing element symbol .
5. Auxiliary Devices: Indicators, trip circuits, and annunciators are represented with small icons like LEDs, lamps, or block symbols to show status or control signals .

Practical Use

• Schematic Interpretation: Engineers use these icons to understand relay operation, interlocks, and protection logic.
• Design and Documentation: Standardized symbols ensure consistency across drawings, manuals, and international projects.
• Safety and Maintenance: Clear representation of relay functions helps in troubleshooting and ensures correct operation of protection systems. By combining IEC graphical symbols with ANSI device numbers, protection engineers can accurately represent and interpret relay functions in complex electrical systems .