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: 7.0 Watts, backplane supplied
- Sample Resolution: 16-bit high-resolution ADC per analog channel
- Hot-Swap Capability: Live insert/remove with automatic CT shorting logic
- Measurement Accuracy: 0.2% full scale; 0.1% for metering mode
- Diagnostic Coverage: CT saturation, open CT/VT, phase imbalance, polarity error
UR-8LH
The Real-World Problem It Solves
Base relay CPU boards lack high-density analog inputs and robust signal validation. External diagnostic add-ons cost extra and complicate wiring.
Where you’ll typically find it:
- Standard distribution substations (115kV–230kV) with 3-phase + ground protection
- Industrial plant switchgear (motors, feeders, small transformers)
- Generator auxiliary systems requiring basic voltage/frequency synchronization
Bottom line: It’s the factory-default, cost-effective 4CT/4VT solution with built-in diagnostics—no extra hardware needed for most applications.
Hardware Architecture & Under-the-Hood Logic
UR-8LH uses a dedicated analog signal processor and four independent CT/VT front-ends, galvanically isolated from the UR backplane. It shares the same backplane slot as UR-8HH/8LA but with standard gain and density.
- 4 CT and 4 VT secondary signals enter individual surge suppression and limiting circuits.
- Precision burden resistors and fixed-gain amplifiers condition signals for standard protection levels.
- Eight 16-bit ADCs convert analog waveforms to digital samples simultaneously.
- Onboard DSP runs real-time diagnostics: flags saturation, open circuits, and phase imbalance.
- Time-aligned, fault-checked data transfers across isolated backplane to host relay CPU.
- Non-volatile memory stores factory calibration; retains settings during hot-swap.
Field Service Pitfalls: What Rookies Get Wrong
Ignoring Diagnostic Threshold CalibrationNew techs leave default settings for saturation/open detection. Factory thresholds are too tight for noisy substation environments, triggering false alarms.
- Field Rule: Bump saturation threshold up 10–15% for feeders with inrush; set open CT detection to 5% of nominal load.
Incorrect Ground CT PolarityTechs wire the ground CT in reverse relative to phase CTs. This flips residual current vector, blinding ground fault protection.
- Field Rule: Match H1/X1 polarity on all CTs (phase + ground); perform secondary injection test before energizing.
Underestimating Heat in Mixed Module RacksMixing UR-8LH with high-power modules (UR-8LA/8HH) in adjacent slots raises ambient temps. Sustained heat degrades ADC accuracy and shortens service life.
- Quick Fix: Maintain 1-inch side airflow; keep cabinet temps <50°C; clean filter baffles quarterly.
UR-8LH
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.
