Article Overview
Relay protection correspondence tables map protective relay functions to standard device numbers, helping engineers identify, select, and apply relays according to ANSI/IEEE or IEC standards.
Overview of Relay Device Numbering
Protective relays are commonly identified by standard device numbers defined by ANSI/IEEE C37.2 in North America and by IEC 60617/617 internationally . These numbers correspond to specific relay functions, making it easier to design, document, and maintain protection schemes. Letters or suffixes are often added to indicate application-specific variations (e.g., 86T for a transformer lockout relay, 59B for bus overvoltage, 50N for instantaneous overcurrent), .
Common ANSI/IEEE Device Numbers
| Device Number | Function | Example Application |
|---|---|---|
| 50 | Instantaneous Overcurrent | Line or feeder protection |
| 51 | Time-Overcurrent | Phase or ground protection |
| 50N / 51N | Neutral Instantaneous / Time-Overcurrent | Ground fault protection |
| 27 | Undervoltage | Bus or transformer undervoltage |
| 59 | Overvoltage | Bus or transformer overvoltage |
| 46 | Negative Sequence | Unbalanced load or phase loss |
| 87 | Differential | Transformer, generator, or bus differential protection |
| 86 | Lockout | Trip and lockout of equipment |
| 81 | Frequency | Over/under frequency protection |
| 32 | Directional Power | Directional power or reverse power protection |
Suffixes like T (transformer), B (bus), or N (neutral) specify the application context .
IEC Device Numbering
IEC standards use different symbols and terminology but serve the same purpose: to identify relay functions consistently across diagrams and documentation . IEC numbers are often accompanied by graphical symbols in schematics, which are standardized under IEC 60617.
Practical Use in Protection Schemes
Relay protection correspondence tables are used to:
- Select appropriate relays for generators, transformers, lines, and capacitor banks .
- Design protection circuits including trip, close, indication, and alarm functions.
- Ensure coordination between relays for selective tripping and system reliability.
- Reference in testing and commissioning procedures for substations .
Additional Notes
- Modern relays include electromechanical, digital, and electronic types, with timing, monitoring, and interface functions .
- Tables often include time ranges, operating characteristics, and terminal connections for practical implementation .
- Using a correspondence table ensures reliability, selectivity, and speed in isolating faults while minimizing disruption to the rest of the system .
In summary, a Relay Protection Correspondence Table provides a standardized mapping of relay functions to device numbers, facilitating proper selection, application, and documentation of protective relays in power systems according to ANSI/IEEE or IEC standards .
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