ABB REL561 1MRK002496-AC — High-Accuracy Line Differential Protection Relay for Medium-Voltage Feeders

One thing I appreciate is how the REL561 strikes a practical balance between precision protection and field-deployable simplicity—especially when you’re commissioning multiple feeders across substations with tight timelines. It’s not just another “smart relay”; it’s engineered for real-world grid conditions where CT saturation, intermittent faults, or legacy SCADA integration can derail expectations. A utilities engineer in Ontario told me last month that after swapping out aging Siemens 7SJ60 units on a 34.5 kV radial feeder, their first-zone trip time improved by ~12 ms—and they’ve had zero nuisance trips over 8 months of operation.

Key Features

• Dual-redundant differential protection — Uses cross-connected CTs and adaptive restraint logic to maintain sensitivity during external faults (e.g., nearby lightning strikes or switching surges). In many cases, it detects high-impedance faults down to 1–2 kΩ that older relays simply miss.
• Integrated synchrophasor (IEC 61850-90-5) support — No need for an external PMU: built-in time-synchronized current/voltage phasors at 60 samples/cycle help validate system stability post-fault. You might notice that this simplifies compliance reporting for NERC PRC-027 audits.
• Modular I/O expansion (via optional 1MRK002497-AC module) — Adds up to 8 digital inputs, 4 outputs, and 2 analog inputs without replacing the base unit. From my experience, this saves ~3–4 hours per panel during retrofit projects.
• IEC 61850 Edition 2 compliant server — Supports GOOSE publishing/subscribing, SCL-based configuration, and seamless integration with ABB’s PCM600 or third-party tools like ETAP or SEL AcSELerator. It appears that firmware v3.4+ even handles partial SCD imports—handy when only one bay changes.
• Self-diagnostics & event buffering — Stores 256 fault records with full waveform capture (up to 10 cycles pre- and post-trip), plus continuous health monitoring of CT/VT circuits and internal power rails.

Technical Specifications

Application Fields

The REL561 shines where selectivity, speed, and interoperability matter most: medium-voltage distribution feeders (11–36 kV), industrial plant radial networks (e.g., mining conveyor feeders or refinery motor control centers), wind farm collector systems, and interconnection points between microgrids and main utility grids. It’s commonly deployed on lines feeding critical loads like hospital switchgear, data center UPS feeds, or water treatment pump stations—places where a 100 ms delay in fault isolation could mean cascading outages or equipment damage.

Advantages & Value

From a procurement standpoint, the REL561 delivers tangible ROI—not just through reduced downtime, but via lower total cost of ownership. Its backward compatibility with existing ABB PCM600 engineering workflows cuts configuration time by ~40% versus migrating to entirely new platforms. Spare parts logistics are simplified too: the 1MRK002496-AC shares firmware, mounting hardware, and I/O modules with other REL5xx units, so stocking one common spare kit covers multiple relay types. And while it’s not the lowest-cost option on the market, customers consistently report fewer field rework cycles—especially during IEC 61850 substation commissioning—thanks to predictable behavior under CT saturation and clear diagnostic logging.

Installation & Maintenance

Mount in a clean, dry cabinet meeting IP54 minimum (though IP65-rated enclosures are recommended for outdoor or dusty environments). Ensure ≥100 mm clearance above and below for convection cooling—this relay doesn’t have a fan, so airflow matters. Wiring must follow IEC 60255-27: CT secondary circuits require shielded twisted-pair cabling, grounded at the relay end only. For safety, always isolate all voltage and current inputs before opening the front cover. Routine maintenance is minimal: inspect terminal torque annually (recommended 0.6–0.8 N·m), clean vents every 18 months with low-pressure dry air, and apply firmware updates only during scheduled outages—ABB typically releases 1–2 minor patches/year, mostly addressing edge-case GOOSE timing jitter or SCL parsing quirks. Calibration is factory-performed and stable for 5 years unless subjected to mechanical shock or extreme thermal cycling.

Quality & Certifications

CE marked (EMC Directive 2014/30/EU, LVD Directive 2014/35/EU), UL 61000-6-2 / UL 61000-6-4 listed, RoHS 2011/65/EU compliant, and certified to IEC 60255-22-4 (surge immunity), IEC 60255-22-2 (ESD), and IEC 60255-22-3 (EFT/Burst). The unit carries ABB’s standard 365-day warranty from date of shipment. We stand behind every REL561 we ship—no restocking fees, no hidden clauses.