Description
Hard-Numbers: Technical Specifications
- CT Channel Count: 4 isolated current inputs (3-phase + ground)
- VT Channel Count: 4 isolated AC voltage sensing inputs
- CT Nominal Rating: Software selectable 1A / 5A secondary
- VT Nominal Rating: Software selectable 67V / 120V
- Operating Temperature: -40°C to +70°C ambient cabinet rating
- Isolation Rating: 2500Vrms reinforced isolation, field to backplane
- Maximum Power Draw: 6.5 Watts, backplane supplied
- Sample Resolution: 16-bit ADC per channel (standard accuracy)
- Hot-Swap Capability: Live insert/remove with automatic CT shorting
- Measurement Accuracy: 0.5% full scale (protection grade, non-metering)
- Diagnostic Coverage: Basic fault detection only (no saturation/phase loss alerts)
The Real-World Problem It Solves
High-end modules (UR-8LH/8HH) add unnecessary cost for simple feeders or non-critical aux systems. Basic relay I/O lacks enough CT/VT points for even standard 3-phase monitoring.
Where you’ll typically find it:
- Distribution feeders (115kV and below) with basic overcurrent/overvoltage protection
- Industrial plant non-critical motors, pumps, and auxiliary switchgear
- Small substations with limited budget and no precision metering requirements
Bottom line: It’s the low-cost, drop-in 4CT/4VT solution for basic protection and monitoring—no extra features you won’t use.
Hardware Architecture & Under-the-Hood Logic
UR-8LM uses a simple analog front-end and shared DSP core, galvanically isolated from the UR backplane. No dedicated diagnostic hardware—relies on base CPU for minimal fault checking.
- 4 CT and 4 VT signals enter basic surge suppression and limiting circuits.
- Fixed-gain amplifiers condition signals for standard protection-level measurements.
- 8 shared 16-bit ADCs convert analog waveforms to digital samples.
- Minimal onboard processing: only out-of-range and short-circuit flagging.
- Raw, unfiltered data transfers across isolated backplane to host relay CPU.
- Factory calibration stored in non-volatile memory; no user trim points.
Field Service Pitfalls: What Rookies Get Wrong
Confusing UR-8LM with UR-8LHTechs mix up basic (LM) and enhanced (LH) modules during replacement. LM lacks diagnostics and has lower accuracy, causing missing alarms or measurement drift.
- Field Rule: Verify part number and revision; LM has no “Enhanced Diagnostics” label on the front panel.
Overloading Accuracy for MeteringNew techs deploy UR-8LM for revenue-grade metering. Its 0.5% accuracy fails utility standards, leading to billing disputes.
- Quick Fix: Use UR-8LH (0.2% accuracy) for metering; reserve LM for protection-only circuits.
Ignoring Basic Wiring PolarityTechs reverse CT/VT polarity on LM’s basic inputs. Without diagnostics, the relay sees incorrect phase angles and misoperates during faults.
- Field Rule: Match H1/X1 polarity on all CTs/VTs; perform secondary injection test to validate phase sequence.
Commercial Availability & Pricing Note
Please note: The listed price is for reference only and is not binding. Final pricing and terms are subject to negotiation based on current market conditions and availability.
