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​