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Nanocrystalline Current Transformer Cores: Class 0.2s Accuracy

High-permeability Nanocrystalline cores designed for Class 0.2s accuracy metering. Saturation flux density: 1.2T. Frequency range: 50Hz-400Hz. Phase angle error: <10 minutes at rated burden.

Written by Manoj Kumar, Founder & Chief Technologist
IEC 61869-2 Compliant

In stock, buy online

PBT cased toroids used for metering CTs, protection CTs, and ground-fault sensors. The CC-NC-CT series below remains available to quote.

Arriving October 20, 2026

Additional HF toroids for RCD/GFCI sensing and larger CT sizes. Dimension diagrams are shown until product photos are available. Request a quote or join the waitlist on each product page.

Technical Specifications

ParameterNanocrystallineMu-MetalSilicon Steel
Initial Permeability (μi)80,00020,0002,000
Saturation Flux Density (Bs)1.2T0.8T1.8T
Remanence (Br)0.05T0.3T1.2T
Core Loss @ 50Hz, 0.1T2 W/kg5 W/kg8 W/kg
Phase Angle Error<10 minutes15-30 minutes30-60 minutes
Temperature Stability±2% (-40°C to +130°C)±5%±8%
Hysteresis LossMinimalLowModerate

Why Nanocrystalline Excels for CT Applications:

The combination of high permeability (80k μi) and low remanence (0.05T) enables accurate measurement at low primary currents while maintaining linearity up to 1.2T saturation. This wide dynamic range is critical for Class 0.2s metering accuracy across 5-120% of rated current.

CT Series Product Specifications

Made-to-order toroidal cores for Class 0.2s metering and protection. Stocked CT-capable sizes are listed above.

Download Technical Datasheet (PDF)

CC-NC-CT-001-26

Dimensions

26×16×10 mm

Ae

50 mm²

le

66 mm

Ve

3,300 mm³

Primary Current5-100A
Accuracy Class0.2s, 0.5s
ApplicationsRevenue metering

CC-NC-CT-002-40

Dimensions

40×30×15 mm

Ae

75 mm²

le

110 mm

Ve

8,250 mm³

Primary Current50-500A
Accuracy Class0.2s, 0.5s, 1.0
ApplicationsMetering, Protection

CC-NC-CT-003-50

Dimensions

50×30×15 mm

Ae

150 mm²

le

126 mm

Ve

18,900 mm³

Primary Current100-2000A
Accuracy Class0.2s, 0.5s, 1.0
ApplicationsHV Protection, GIS

CC-NC-CT-004-40G

Dimensions

40×30×15 mm

Ae

75 mm²

le

110 mm

Ve

8,250 mm³

Primary Current50-500A
Accuracy Class0.2s, 0.5s, 1.0
ApplicationsMetering, Protection

Magnetic Parameters

  • • Initial permeability: 80,000 ± 25%
  • • Saturation induction: 1.2T @ 800 A/m
  • • Remanence: <0.05T
  • • Coercivity: <1.5 A/m

Electrical Performance

  • • Phase angle error: <10 minutes
  • • Ratio error: <0.2% (Class 0.2s)
  • • Secondary burden: 2.5-15 VA
  • • Frequency range: 50-400 Hz

Environmental

  • • Operating temp: -40°C to +130°C
  • • Humidity: 95% RH non-condensing
  • • Vibration: IEC 60068-2-6
  • • Insulation: 3kV AC (1 min)

Performance Characteristics

Permeability vs Frequency Response

μi remains >60k up to 10kHz

Flat response enables wideband CT accuracy

Key Points:
  • Initial permeability: 80,000 ± 25% @ 1kHz
  • Maintains >60k μi up to 10kHz
  • Enables accurate harmonic measurement
  • Superior to ferrite above 1kHz

B-H Hysteresis Loop (50Hz)

Bs = 1.2T, Br = 0.05T

Minimal remanence for CT accuracy

Magnetic Properties:
  • Saturation induction: 1.2T @ 800 A/m
  • Remanence: <0.05T (excellent linearity)
  • Coercivity: <1.5 A/m
  • Core loss: 2 W/kg @ 50Hz, 0.1T

Phase Angle vs Current Loading

Phase error <10 minutes

5-120% current range (Class 0.2s)

Accuracy Performance:
  • Phase angle error: <10 minutes @ rated burden
  • Ratio error: <0.2% (5-120% In)
  • Composite error: <0.5% @ 5% In
  • Meets IEC 61869-2 Class 0.2s requirements

Temperature Stability

±2% drift (-40°C to +130°C)

Stable across full operating range

Environmental Performance:
  • Permeability drift: ±2% over temp range
  • Operating: -40°C to +130°C
  • Storage: -55°C to +150°C
  • Humidity: 95% RH non-condensing

Typical Applications & Case Studies

400kV GIS Revenue Metering

Integrated into 400kV Gas Insulated Switchgear for protection and metering. CC-NC-CT-003-50 cores achieve Class 0.2s accuracy for 1000/1A ratio with 2.5VA burden at 50Hz.

Standards: IEC 61869-2, ANSI/IEEE C57.13
Environment: SF6 gas, -25°C to +40°C
Performance: Phase error <8 minutes, ratio error <0.15%

Differential Protection Relay

CC-NC-CT-002-40 cores in busbar protection systems requiring fast, accurate fault detection. Maintains linearity during 20x overcurrent conditions.

Application: 132kV substation busbar protection
Fault Current: 40kA symmetrical
Response Time: <2ms to 95% accuracy

Smart Grid Power Quality

Real-time monitoring of harmonics up to 50th order in renewable energy integration. CC-NC-CT-001-26 maintains accuracy across 5-400Hz bandwidth.

THD Measurement: <0.1% error up to 2kHz
Dynamic Range: 1% to 120% of rated current
Sampling Rate: Compatible with 10kHz ADCs

DC-Tolerant Protection

CC-NC-CT-004-40G gapped cores for HVDC converter stations and renewable energy systems with DC bias components up to 10% of AC rating.

DC Tolerance: 100A DC bias with 1000A AC
Saturation Margin: >2x at maximum DC+AC
Applications: Wind farms, solar inverters, HVDC

Engineering FAQ: CT Core Selection

How to choose a CT core for high-precision metering?

For Class 0.2s accuracy, calculate the required turns ratio using Np/Ns = Is/Ip. Ensure the core's saturation flux density (1.2T for nanocrystalline) provides adequate margin above the maximum flux: Φmax = (Ip × √2 × Zb) / (2πf × Ns)

Example: For 1000/1A CT with 2.5VA burden at 50Hz:
Φmax = (1000 × 1.414 × 2.5) / (2π × 50 × 1000) = 0.011 Wb
Required Ae ≥ 0.011/1.2 = 9.2 mm² (CC-NC-CT-002-40 provides 15 mm²)

What accuracy classes can nanocrystalline CT cores achieve?

Nanocrystalline cores readily achieve IEC 61869 Class 0.1, 0.2s, and 0.5s for revenue metering. The low remanence (0.05T) and high permeability (80k μi) enable accurate measurement from 5% to 120% of rated current with phase errors typically <10 minutes.

How does DC bias affect CT core performance?

Standard nanocrystalline cores tolerate DC bias up to 5% of AC rating without significant accuracy degradation. For higher DC content (renewable energy, HVDC), use gapped cores like CC-NC-CT-004-40G which maintain linearity with DC bias up to 10% of AC rating.

What's the difference between Class 0.2 and Class 0.2s?

Class 0.2s has tighter phase angle requirements (±10 minutes vs ±30 minutes) and extended accuracy range (5-120% vs 20-100% of rated current). This makes 0.2s suitable for revenue metering where accurate measurement at light loads is critical.

How to calculate secondary burden for CT design?

Total burden = Meter burden + Lead resistance + Safety factor. For revenue metering:

Zb = Zmeter + (2 × ρ × L / A) + 25% safety margin
Where: ρ = 0.0175 Ω·mm²/m (copper), L = lead length, A = conductor area

Need CT Core Design Support?

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About the author: Manoj Kumar is Founder and Chief Technologist at CenturaCores, focused on nanocrystalline core technology, metering CTs, and manufacturing-aligned design for utility and industrial applications.

Standards Compliance: All CenturaCores CT products are designed and tested to IEC 61869-2, ANSI/IEEE C57.13, and relevant national standards.