ABB REX521GHHGSH51G Medium-Voltage Protection Relay

Description

Product overview

The ABB REX521GHHGSH51G is intended for power distribution applications where feeder circuits require coordinated protection, operational control, and electrical measurements. The REX 521 platform was developed for medium-voltage networks and can be applied to incoming and outgoing feeders, motor feeders, and selected backup-protection duties. Its available functions depend on the relay’s specific hardware version and configured protection application; the complete model code should therefore be checked against the installed unit and its technical documentation rather than treated as a generic identifier.

In a substation or industrial power system, the REX 521 can receive signals from conventional current and voltage transformers, evaluate electrical conditions, and support configured protection and circuit-breaker control functions. The family includes standard configurations for different network earthing arrangements, but the correct configuration depends on the actual installation, transformer connections, protection coordination study, and operating requirements. The relay’s measurement and supervision capabilities can help maintenance teams investigate faults and assess circuit status.

For replacement procurement, the ABB REX521GHHGSH51G requires particular attention because the REX 521 family is no longer an active product line. A matching family name alone does not establish interchangeability. Before installing a replacement, compare the complete type designation, terminal layout, current and voltage input ratings, auxiliary supply, communication protocol, configured functions, and existing settings. For critical feeder or motor protection, confirm relay operation through an appropriate test procedure before returning the circuit to service. The unit’s actual condition and the scope of any supplier testing should be documented rather than inferred from a visual inspection.

Product introduction

The REX521GHHGSH51G is intended for protection and supervision tasks in medium-voltage distribution systems. Its suitability for a specific feeder or motor depends on the installed configuration and the protection functions enabled for that application.

Because this is a legacy relay, buyers should verify the full nameplate code, terminal condition, power-up behavior, and test evidence before committing to a replacement. A relay that powers on is not necessarily a relay that will perform correctly under fault conditions.

Key technical specifications

Family-level details are documented in ABB’s REX 521 technical reference material. They should not be assumed to apply identically to every hardware version.

REX521GHHGSH51G

Related products and equipment

The following are related ABB protection relays or components that may arise during a retrofit or maintenance project. They are not confirmed drop-in replacements for REX521GHHGSH51G.

• ABB REF 541 / REF 543 / REF 545 — feeder protection relay family.
• ABB REF 610 — feeder protection relay.
• ABB REM 543 / REM 545 / REM 610 — motor protection relay family.
• ABB RET 541 / RET 543 / RET 545 — transformer protection relay family.
• ABB REU 610 — voltage protection relay.

Confirm each alternative against the required protection functions, CT/VT inputs, communication requirements, engineering tools, and system approval process. ABB lists these families in its legacy relay documentation and connectivity references.

Frequently asked questions

Q1: What is the ABB REX521GHHGSH51G used for?

It belongs to the REX 521 feeder protection relay family, used for protection, control, measurement, and supervision in medium-voltage networks. The family also supports selected three-phase AC motor protection applications.

Q2: Is this relay still in production?

ABB identifies the REX 521 family as discontinued since 2012. Availability is therefore likely to depend on existing stock, tested surplus units, or repair and exchange channels.

Q3: Can I replace an existing REX 521 relay with this model?

Only after confirming the full type code and hardware configuration. Compare auxiliary supply, current and voltage inputs, terminal assignments, firmware, communication options, and protection settings before installation.

Q4: Can the relay be hot-swapped?

Do not assume hot-swap capability. Follow the applicable ABB instructions and site isolation procedures. Protection circuits and associated trip wiring must be handled under the plant’s approved electrical safety process.

Q5: What testing should be requested from a supplier?

Request the unit’s nameplate and serial-number photographs, visual inspection results, auxiliary power-up checks, display and diagnostics checks, communication checks where applicable, and documented secondary-injection or functional test results appropriate to the configured protection functions.

Q6: Does a used relay retain the original protection settings?

Not necessarily. Settings may be missing, altered, or incompatible with the target installation. Back up and compare the existing configuration, then verify all protection settings and trip logic before commissioning.

Q7: What should be confirmed before purchase?

Confirm the complete model code, hardware revision, auxiliary supply, CT/VT input ratings, required communication interface, configuration, physical condition, test scope, and return or warranty terms.

Procurement recommendation

For ABB , prioritize exact identification and documented functional testing over a general “tested” or “working” claim. Ask the supplier to provide:

• Clear photographs of the nameplate, front panel, terminals, and labels.
• Confirmation of the exact type designation and hardware revision.
• A written description of the inspection and testing performed.
• Details of any repairs, replaced components, or known faults.
• Confirmation of included accessories and applicable warranty terms.