ABB REX521GHHPSH51G｜Protection Relay｜

REX521BBHGLB01C

1. Digital Input and Output Relay Testing

The relay allows users to test:

Digital input channels
General output relays
Protection-related output contacts
Internal fault indication relay (IRF)

Testing can be initiated through:

Local Human-Machine Interface (HMI)
Serial communication connection
2. Test Mode Operation

In normal operation, the relay protection and control logic is connected directly to the physical input and output interfaces.

To test digital inputs and most output relays, the relay must first be placed into Test Mode.

Test Mode Activation

Test mode can be enabled through a configurable parameter.

When test mode is active:

The green READY LED begins blinking.
The relay indicates that it is operating in a test state.
Protection and control input processing is separated from physical input changes.
3. Isolation of Physical Inputs During Testing

When the relay enters test mode:

The normal relay configuration is disconnected from physical inputs.
Changes applied to digital input terminals are ignored by the protection logic.
Test signals can be applied without affecting normal protection functions.

This prevents accidental operation of protection schemes during commissioning activities.

4. Test Mode Deactivation

When test mode is disabled:

Test parameters requiring test mode are automatically reset.
The relay returns to normal protection operation.
Physical inputs and outputs resume normal configuration control.

This ensures that temporary test settings cannot remain active after maintenance work is completed.

5. Output Relay Testing
Output Relay Activation Through Communication

General output relays can normally be tested through:

HMI commands
Serial communication commands

A special feature allows output relays to be activated through serial communication without entering test mode.

This capability is intended for applications where output contacts are used for:

External signaling
Auxiliary control functions
Customer-specific automation purposes

These applications are separate from the main protection and control functions of the relay.

6. Internal Relay Fault (IRF) Relay Testing

The IRF relay provides indication of internal relay failures.

Testing requirements:

IRF testing is performed through the HMI.
The relay must always be placed into test mode before IRF testing.

The test verifies:

Internal fault indication circuits
Alarm output functionality
External monitoring system response
7. Restrictions During Output Relay Testing

When testing general output relays, users must consider that the relay’s normal operating logic cannot be completely disconnected.

If an output relay is:

Permanently activated by the relay configuration, or
Continuously driven by protection/control logic,

then it cannot be switched off during testing.

This behavior prevents test operations from overriding active protection or control commands.

Commissioning and Maintenance Considerations

During commissioning, the recommended procedure is:

Enable relay test mode.
Verify READY LED blinking indication.
Test digital inputs.
Test output relay operation.
Verify IRF alarm output if required.
Disable test mode.
Confirm relay returns to normal operating state.
Summary

The ABB REU615 provides comprehensive relay testing functions through both HMI and serial communication. Test mode separates physical inputs from the active protection logic, allowing safe verification of digital inputs and outputs. The READY LED provides clear indication of test status, while automatic reset of test parameters prevents unintended operation after maintenance. Output relay testing without test mode is available for external auxiliary applications, while IRF relay testing requires mandatory test mode activation. These features simplify commissioning and improve reliability during lifecycle maintenance.