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

Rockwill

17yrs 700++ staff 108000m²+m² US$150,000,000+ China

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:

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.

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.

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:

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.
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.
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.
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.
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

Indicator Category	Measurement Parameter	Performance Value	Core Significance
Measurement Bandwidth	(Rogowski)	0.1 Hz - 2 MHz	Covers transients & high-frequency harmonics
Measurement Accuracy	(LPCT @ Power Freq)	0.2S Class	Meets precision metering & protection requirements
Measurement Accuracy	(Full Bandwidth Composite)	< ±0.5%	Ensures high precision across the entire domain
Digitization	Sampling (ADC)	16-bit / 200 kSPS (AD7606)	High-precision on-sensor digital conversion
Digitization	Output Protocol	IEC 61850-9-2LE (Fiber)	Seamless access to digital substations
Anti-Interference	Shielding Material	Permalloy (μ ≥ 10⁴)	Resists strong internal GIS electromagnetic interference