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Intro to Relays #2 - ANSI/IEEE Relay Numbers
Protective relays represent a specialized niche within electrical engineering and contracting, often perceived as complex. But they don't have to be intimidating! This series of three articles aims to demystify basic relaying concepts for professionals in the solar and energy storage sectors who aren't engineers.
**Introduction to Relays #1: What Are Relays, CTs, and PTs?**
**Introduction to Relays #2: ANSI/IEEE Relay Device Numbers (found below)**
**Introduction to Relays #3: What Does SEL Stand For?**
### Relay Numbers
Protective relays are designed using standard device numbers to describe their functionality. Instead of lengthy verbal descriptions, we rely on numerical codes to specify the roles of these devices. These numbers and acronyms are standardized in the document ANSI/IEEE C37.2.
### Why Use Numbers Instead of Words?
1. **Efficiency**: Using numbers saves time and effort. For instance, saying "Over Voltage on the Neutral" takes longer than simply stating "59N."
2. **Standardization**: In conversations, everyone involved—from utilities to engineers, vendors, and installers—understands the intended functionality instantly, reducing the chance of miscommunication.
3. **Compactness**: Drawings become clearer and less cluttered when describing multiple functions. For example, labeling a relay with "phase overvoltage & undervoltage, phase over frequency & under frequency, ground inverse time overcurrent, and alarm" becomes much simpler when written numerically.
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### Commonly Used Relay Functions in Solar Systems
Below are some of the most frequently utilized relay functions in photovoltaic (PV) and energy storage systems:
| Number | Name | Description |
|--------|---------------------|-----------------------------------------------------------------------------|
| 25 | Synchronizing Clock | Compares utility and solar circuit voltages, frequencies, and phase angles. If matched, it allows solar systems to connect in parallel with the grid. |
| 27 | Undervoltage | Activates when voltage drops below a preset value. |
| 32 | Directional Power | Triggers when power flow exceeds a set limit in a specific direction. |
| 49 | Transformer Thermal | Alerts when the temperature of a winding surpasses a predefined threshold. |
| 50 | Instantaneous Overcurrent | Activates when current exceeds a defined value. |
| 51 | Inverse-Time Overcurrent | Activates when current exceeds a value for a specified duration. |
| 52 | Circuit Breaker | A device used to open circuits. Adding 'R' indicates it can also reclose circuits. |
| 59 | Overvoltage | Triggers when voltage goes above a set point. |
| 74 | Alarm | Initiates visual, audible, or data alarms. |
| 79 | AC Reclosing | Manages the reclosing or locking out of an AC circuit interrupter. |
| 81 | Frequency | Activates when frequency falls outside the acceptable range. |
| 86 | Lockout | Prevents device operation until manually reset. |
| 87 | Differential Protective | Triggers upon detecting a difference between two measured currents. |
| 89 | Line Switch | Refers to devices like disconnect switches. '89' is typically used when electrical accessories are present. |
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### Additional Descriptors After Numbers
Sometimes letters follow the numbers to further define the function:
| Number | Name | Description |
|--------|---------|----------------------------------------------------------------------|
| R | Reclosing | Indicates the ability to reclose circuits. Example: 52R is a circuit breaker that opens and recloses circuits. |
| P | Phase | Specifies the function applies to the phases. Often omitted since it's implied, e.g., 50 and 51 overcurrent functions. |
| N | Neutral | Denotes the function operates on the neutral rather than the phase. Example: 51N monitors the neutral for unbalanced overcurrent. |
| G | Ground | Indicates the function targets the ground instead of the phase. Example: 51G monitors ground bonding for ground faults. |
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### Setpoints
Simply listing functions isn’t sufficient; setpoints—minimum and/or maximum values—are equally crucial. Engineers determine these values, and they often vary from project to project.
### Conclusion
At first glance, relay device numbers seem straightforward. Yet, delving deeper reveals increasing complexity. While developers and project managers don’t need to master the technicalities, having experienced engineers ensures smooth execution. Need assistance with protective relays on your project? Click [here](#) to learn more or contact us today.
This series aims to bridge gaps between technical knowledge and practical application, empowering non-engineers in renewable energy fields. Stay tuned for future articles!