ABB REJ 525 Ground Fault Relay

1. Product Overview

The ABB REJ 525 Ground Fault Relay is a protection relay for medium and low voltage power systems, designed to detect ground fault currents and provide alarm or trip signals.
It offers high-accuracy detection, fast response, and configurable modes, widely used in power plants, substations, industrial facilities, and distribution networks to protect equipment and ensure personnel safety.

2. Technical Specifications

• Model: REJ 525

• Type: Ground Fault Relay

• Rated Voltage: AC 110–240 V / DC 24–48 V (model dependent)

• Monitoring Current Range: 10 mA – 5 A (adjustable)

• Detection Type: Residual current / Zero-sequence current

• Operating Delay: 0.1 s – 10 s (adjustable)

• Relay Output: 1 or 2 SPDT relay contacts

• Alarm Function: Configurable ground fault alarm, notification, and remote signaling

• Communication Interface: Optional RS485 / Modbus RTU

• Operating Temperature: ‑20 ℃ – +60 ℃

• Mounting: DIN rail

• Protection Class: IP20

• Standards Compliance: IEC 60255-5 / IEC 60255-6

3. Key Advantages & Features

1. High-Accuracy Ground Fault Detection
   Sensitive to low-level ground fault currents for quick detection.

2. Fast Response & Adjustable Delay
   Fast action with configurable delay to optimize protection flexibility.

3. Multi-Functional Output
   Relay outputs can be used for alarm, trip, or remote signaling for layered protection.

4. Multiple Monitoring Modes
   Supports residual current, zero-sequence current, and system unbalance detection.

5. Easy Installation & Integration
   DIN rail mounting for seamless integration with control cabinets and automation systems.

6. Reliable & Durable
   Industrial-grade design with strong interference immunity for long-term operation in harsh environments.

4. Typical Applications

• Low-voltage distribution protection in industrial plants

• Ground fault monitoring in power plants and substations

• Electrical distribution system leakage protection

• Critical infrastructure such as hospitals and data centers

• Oil & gas, mining, and metallurgical industries

5. Installation & Usage Notes

1. System Current Matching
   Ensure relay monitoring current range matches system zero-sequence current to avoid misoperation.

2. Proper Wiring
   Connect CTs, power supply, and relay outputs according to the manual; ensure proper grounding.

3. Set Operating Delay
   Configure delay according to protection requirements to balance safety and false-trip prevention.

4. Environmental Conditions
   Avoid high humidity, corrosive gases, and strong electromagnetic interference.

5. Regular Testing
   Periodically check relay operation and alarm functionality to ensure system reliability.

The structure and details of the product：

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