ABB REX521GHHPSH51G — Compact, IEC 61850-Enabled Protection Relay for Feeder & Transformer Applications

It’s not often you find a relay that balances DIN-rail simplicity with full substation-grade functionality—but the REX521GHHPSH51G does exactly that. From my experience supporting utilities and panel builders across Europe and Southeast Asia, this model has become a go-to for medium-voltage feeder protection where space is tight, but reliability can’t be compromised. One customer in Poland recently replaced aging Siemens SIPROTEC 3 devices on a 20 kV ring-main unit—and reported zero configuration surprises during commissioning, thanks to ABB’s consistent logic editor and native IEC 61850 MMS/GOOSE mapping.

Key Features

• IEC 61850 Class 2 compliance (MMS + GOOSE) — Enables direct integration into modern SCADA and substation automation systems without gateways. In many cases, it eliminates the need for separate protocol converters.
• Integrated 3-phase overcurrent + earth-fault + thermal overload protection — Includes ANSI/IEEE-style time-current curves (IEC & IEEE inverse, very inverse, extremely inverse) plus user-definable multi-step functions.
• Embedded Ethernet port + optional RS-485 serial interface — The primary Ethernet port supports dual IP stacks (for redundancy or segregation), while the RS-485 (via optional module) handles legacy RTU communication or metering integration.
• Real-time fault recording & oscillography — Captures up to 100 pre-fault and 200 post-fault cycles at 1 kHz sampling—enough detail to verify coordination with upstream/downstream breakers.
• DIN-rail mount, compact footprint (100 mm width) — Fits two side-by-side in a standard 225 mm wide control cabinet, which matters when retrofitting older panels with limited real estate.

Technical Specifications

Application Fields

This relay shines where flexibility meets ruggedness: urban MV distribution feeders (especially cable networks with loop-in/loop-out configurations), industrial transformer incomers up to 30 MVA, renewable interconnection points (like small-scale solar farms feeding into LV/MV grids), and rail traction power substations. You might notice that customers in water/wastewater plants also favor it—mainly because its IP20-rated enclosure holds up well in humid, non-air-conditioned switchrooms, and its thermal overload function helps protect aging pump motor feeders without adding extra sensors.

Advantages & Value

From a procurement standpoint, the REX521GHHPSH51G avoids common pitfalls: no hidden licensing fees for basic protection functions, no forced migration to cloud-based engineering tools (it works seamlessly with PCM600 v3.2+ offline), and full backward compatibility with older REX521 firmware updates—so your spare parts inventory stays relevant longer. It appears that total cost of ownership drops noticeably when factoring in reduced engineering time (typical project setup takes under 4 hours vs. 1–2 days for some competing platforms) and fewer field commissioning callbacks. And yes—it interoperates cleanly with SEL, GE, and Siemens IEDs in mixed-vendor substations, provided GOOSE datasets are properly mapped.

Installation & Maintenance

Mount it in an IP54-rated cabinet with ≥ 100 mm clearance above and below for convection cooling—no forced ventilation required unless ambient exceeds 55 °C. Wiring should follow IEC 61850-3 EMC guidelines: shielded twisted-pair for analog inputs, separate cable trays for power and signal lines. Safety-wise, always isolate CT/VT circuits before opening terminals; the relay doesn’t include built-in CT shorting—so external test blocks are mandatory. For maintenance: check firmware version every 6 months (ABB typically releases 1–2 minor patches/year), clean vents with dry air annually, and validate time synchronization (IRIG-B or SNTP) quarterly if used for event timestamping. Calibration isn’t needed yearly—ABB’s factory calibration holds for 5 years under normal conditions, though we recommend functional testing at each major outage.

Quality & Certifications

Certified to IEC 61850-10 Ed. 2 (Class II), IEC 60255-26 (EMC), UL 61010-1, CE, RoHS, and KEMA-certified for short-circuit withstand (20 kA, 1 s). ABB backs it with a standard 365-day warranty—extendable to 5 years via service agreement. Unlike some competitors, firmware updates and configuration files remain freely downloadable from ABB’s official support portal without login gates or registration walls.