Rogowski Coil + Low-Power CT (LPCT) Integrated GIS Broadband Current Measurement Solution

Background: In DC transmission converter stations, large-scale electric arc furnaces, and other environments with severe harmonic pollution and high transient conditions, traditional electromagnetic current transformers (CTs) within Gas-Insulated Switchgear (GIS) face significant challenges: limited frequency bandwidth causes distortion of high-frequency and transient signals; measurement accuracy falls short for harmonic analysis and protection requirements; and external merging units (MUs) increase costs and complexity.

Solution: This solution innovatively integrates Rogowski coils and Low-Power Current Transformers (LPCTs) within the GIS enclosure, combined with local digitization technology, providing accurate full-band measurement from near-DC to high frequencies, with direct digital output compliant with the IEC 61850 standard.

Technical Highlights:

1. Dual-Sensor Fusion Technology:

• Rogowski Coil: Responsible for capturing broadband/high-order harmonics/transient currents. Its absence of magnetic saturation ensures linear response within an ultra-wide bandwidth of 0.1 Hz to 2 MHz, accurately capturing fast transient processes in converter stations (e.g., commutation failures) and high-order harmonics up to several hundred times generated by arc furnaces.

• Low-Power CT (LPCT): Responsible for high-accuracy measurement and protection of power frequency fundamentals. It achieves an accuracy class as high as 0.2S, ensuring stable, reliable, and standard-compliant current measurement under fundamental frequency (50/60Hz) and nearby low-order harmonic conditions, meeting the requirements for energy metering and protection signal sources.

• Intelligent Fusion: A data processing unit performs intelligent synchronization and calibration of the two signal paths, achieving seamless stitching across the entire frequency band (0.1 Hz to 2 MHz), outputting a unified, high-precision current data stream.

2. On-Sensor Digitization:

• Sampling: Integrates the high-performance AD7606 ADC chip (16-bit resolution, 200 kSPS sampling rate) directly at the CT mounting flange side.

• Output: Digitized data is transmitted via optical fiber, compliant with the IEC 61850-9-2LE protocol standard, replacing the traditional external merging unit (MU).

• Advantages: Completely eliminates attenuation, noise interference, and grounding issues introduced by long-distance analog signal transmission; significantly simplifies the system structure; enhances signal quality and anti-interference capability.

3. Extreme Anti-Interference Design (Key Reliability Assurance):

• Fusion Unit (MU Module) Structure:

• Enclosure: High-stiffness cast aluminum housing provides mechanical strength and basic electromagnetic shielding.

• Core Shield Layer: Employs Permalloy (magnetic permeability μ ≥ 10⁴), forming an ultra-high permeability magnetic shielding path. The shielding capability of this material for low-frequency strong magnetic fields far exceeds that of ordinary aluminum housings or silicon steel sheets, making it the ideal choice for the harsh electromagnetic environment inside GIS.

Application Scenarios:

• High-Voltage Direct Current (HVDC) Converter Stations: Accurately measures steep wave front (extremely high di/dt) transient currents and characteristic harmonics (e.g., 12k±1 orders generated by 12-pulse systems) produced during converter valve switching, ensuring stable and efficient operation of the DC control and protection system.

• Large Electric Arc Furnaces / Rolling Mills and other Impact Loads: Precisely captures load rapid start/stop, short-circuit currents, and the generated wide-spectrum harmonics (2nd to 50th order and beyond), providing high-fidelity data for power quality analysis, harmonic mitigation, and relay protection.

• Smart Substations: Meets the stringent requirements for current data bandwidth and accuracy from new advanced applications such as Condition-Based Monitoring (CBM), Phasor Measurement Units (PMU), and broadband protection.

Core Advantages:

1. Ultra-High Accuracy Across Full Bandwidth: Comprehensive error strictly controlled within ±0.5% across the entire measurement band (0.1 Hz - 2 MHz), simultaneously meeting high-accuracy power-frequency metering (0.2S class) and high-frequency/transient measurement needs.

2. Breakthrough in Bandwidth Limitations: The Rogowski coil's ultra-wide frequency response (0.1 Hz - 2 MHz) covers DC components, extremely low-order harmonics up to high-frequency RF interference, unattainable by traditional CTs.

3. Significant Cost and Space Savings: Eliminates the external Merging Unit (MU) and associated cabling, installation space, reducing overall system equipment procurement, installation, and maintenance costs by approximately 30%. The GIS main structure becomes more compact.

4. Strong Anti-Interference & Reliable Operation: The combination of a cast aluminum housing and Permalloy magnetic shielding provides exceptional electromagnetic protection, ensuring long-term stable and reliable operation in the harsh GIS environment.

5. Seamless Digital Grid Integration: Native IEC 61850-9-2LE optical fiber digital output, fully compatible with modern digital substation architecture, simplifying secondary wiring.

Key Performance Parameter Overview