Description
The ABB REX521 (incorporating model variant REX521GHHGLH50G) is a comprehensive numerical multifunctional protection and control relay specifically engineered for the protection, control, measurement, and supervision of medium-sized and large AC motors in industrial and utility applications. It integrates advanced thermal overload protection, short-circuit protection, unbalance detection, and motor-start supervision into a single, compact hardware platform.
| Parameter | Specification |
| Brand | ABB |
| Model | REX521 (REX521GHHGLH50G) |
| Series | 500/520 Series Numerical Protection and Control |
| Product Name | Multifunctional Motor Protection Relay |
| Place of Origin | Finland / Sweden / Switzerland |
| Product Status | Mature / Legacy Industrial Support |
| Dimensions | Standard flush mounting case (approx. 216 mm × 177 mm panel cutout) |
| Weight | Approx. 3.2 kg |
| Country of Origin | Finland |
| Power Consumption | Low-voltage auxiliary DC/AC power supply (approx. 15–20 W nominal) |
First-Run Inspection Checklist
- ☑ Physical Integrity Check
Inspect the outer plastic casing, front-panel human-machine interface (HMI) LCD screen, pushbuttons, and rear terminal blocks for any physical shipping damage, cracks, or loose components.
- ☑ Auxiliary Power & Grounding Verification
Verify that the incoming auxiliary control voltage matches the relay nameplate rating using a calibrated multimeter before energization. Ensure the rear protective earth (PE) grounding screw is securely connected to the switchgear earth bar.
- ☑ Hardware & Software Configuration Check
Confirm that the internal relay parameters, protection settings, and communication protocol configurations match the motor coordination study and plant electrical drawings prior to putting the system into service.
Routine Maintenance & Servicing
- 🛠 Environmental Monitoring
Regularly inspect the switchgear compartment climate control to ensure ambient operating temperatures remain within acceptable industrial limits (typically -10°C to +55°C) and free from excessive dust or humidity.
- 🔌 Terminal & Wiring Inspection
Perform periodic visual checks on current transformer (CT) and voltage transformer (VT) terminal blocks to ensure wiring tightness, secure ferrules, and absence of thermal discoloration or loosening from vibration.
Troubleshooting & Common Issues
- ⚠️ Auxiliary Supply Failure or Boot Loops
If the relay display remains unpowered or experiences continuous resetting, check incoming DC/AC auxiliary power supply fuses, measure terminal voltage levels, and verify internal power module status.
- ⚠️ Spurious Motor Tripping or Alarms
If unexpected motor trips occur, review the relay’s internal event recorder and fault logs via the front HMI or engineering software to analyze thermal overload status, phase unbalance levels, or startup time limit violations.
Safety Precautions
- 🔐 Electrostatic Discharge (ESD) Protection
Always utilize a grounded ESD wrist strap and appropriate antistatic procedures if handling internal boards or performing maintenance to safeguard sensitive microelectronics.
- ⚠️ Current Transformer (CT) Circuit Safety
Never open-circuit secondary terminals of live current transformers while the primary motor circuit is energized. Always short-circuit CT secondary windings before disconnecting input wiring to prevent dangerous high-voltage spikes.
Frequently Asked Questions (Q&A)
- ❓ Q1: What are the primary protection functions included in the REX521 relay?
A: The REX521 provides comprehensive motor protection including thermal overload protection, locked rotor protection, earth fault protection, negative phase sequence (unbalance) protection, thermal status tracking, and motor start supervision.
- ❓ Q2: How can relay event logs and configuration settings be accessed locally or remotely?
A: Settings and event logs can be accessed locally via the front-panel alphanumeric display and keypad, or remotely using ABB’s dedicated configuration and communication software tools through the rear communication ports.
