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mart Power Solutions by Rockwill – Engineered for Reliability & Efficiency

Rockwill delivers integrated electrical solutions for smart grids, urban infrastructure, renewable integration, and industrial applications. From medium-voltage automation to EV charging networks and prefabricated substations, our systems ensure stable, efficient, and future-ready power distribution. Customized. Connected. Reliable.

Precision Power Monitoring: High-Accuracy Dual-Ratio Outdoor Digital Current Transformer Solution


Solution Summary:
Our advanced Outdoor Current Transformer (CT) solution integrates ​Multi-Tap Dual-Ratio Sensing​ with a ​Digital Merging Unit (MU)​ to deliver adaptive, high-precision current measurement for dynamic power environments like renewable integration sites. This IEC 61850-compliant system eliminates traditional accuracy/reliability trade-offs by enabling real-time ratio switching and digital data output.

​Core Technology Breakdown

  1. Dual-Ratio Sensing Core
    • Innovation:​ Embedded multi-tap windings supporting ​200:5 and 1200:5​ ratios within a single CT body.
    • Adaptability:​ Software-controlled ratio selection via the MU.
    • Problem Solved:​ Automatically adjusts measurement range to accommodate drastic load shifts (e.g., solar farm daylight fluctuations or wind farm cut-in/cut-out) without physical intervention or overdesigned CTs.
  2. High-Precision Digital Merging Unit (MU)
    • Accuracy:​ Exceeds ​<0.2S Class​ (per IEC 60044-1/IEC 61869) for both revenue metering (ANSI C12.1) and protection functions (IEEE C37.90).
    • Output:​ Native ​IEC 61850-9-2 LE​ sampled values over Ethernet.
    • Calibration:​ Digital signal processing compensates for phase errors & non-linearity.

​Key Features & Advantages

  • Dual-Ratio On Demand:​ Switch seamlessly between 200:5 (low load/high sensitivity) and 1200:5 (high fault current) via software commands – ​no rewiring needed.
  • Substation-Ready:​ Native digital output (9-2 LE) integrates directly into IEC 61850- based protection relays, meters, and control systems.
  • Future-Proof Accuracy:​ <0.2S accuracy ensures compliance with strictest revenue metering standards and enables high-impedance differential protection.
  • Robust Outdoor Design:​ IP67-rated enclosure, UV-resistant polymer housing, and corrosion-resistant materials ensure reliability in harsh environments (-40°C to +70°C).
  • Reduced Installation Cost:​ Single CT installation replaces need for multiple conventional CTs or burdensome auxiliary units.
  • Enhanced Grid Stability:​ Precise, real-time data enables faster protection response for fluctuating fault currents (e.g., inverter-based resource faults).

​Implementation: Renewable Energy Use Case

  • Scenario:​ 200 MW Solar/Wind Farm connection to 138kV substation. Fault currents range from near-zero (offline inverters) to 30kA+ (full output grid fault).
  • Challenge:​ Conventional CTs compromise accuracy at low current (200:5 needed) but saturate at high fault currents (1200:5 needed).
  • Our Solution:
    1. Install dual-ratio CTs at point of interconnection (HV bus/circuit breaker).
    2. During normal operation (<50% load), MU selects ​200:5 ratio​ – capturing granular data for precise energy accounting and flicker monitoring.
    3. Upon fault detection (rapid current rise), MU auto-switches to ​1200:5 ratio​ in <5ms – preventing saturation, maintaining accuracy, and enabling relays to clear faults reliably.
    4. Sampled values transmitted digitally via 9-2 LE to protection relays, meters, and SCADA – eliminating analog wiring errors and converter delays.

​Why This Solution Wins

  • Eliminates Saturation Risk:​ Maintains accuracy across 100:1 dynamic range (e.g., 30A to 3000A primary).
  • OPEX Savings:​ Remote configuration/ratio switching reduces site visits.
  • Safety Boost:​ Digital isolation replaces dangerous CT secondary opens.
  • Data Integrity:​ Digital output avoids signal degradation from EMI/RFI.
  • Compliance Ready:​ Designed to meet IEEE 1547-2018 fault ride-through requirements for renewables.
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