What Is The Difference Between Split-Core Current Transformer And Rogowski Coil?

01 01, 2026

In modern electrical systems, accurate current measurement is crucial for energy monitoring, protective relaying, and power quality analysis. Among the widely used current sensing devices, the split-core current transformer and the Rogowski coil stand out for their distinct characteristics, applications, and installation requirements. Understanding the differences between these two types of devices is essential for engineers, procurement specialists, and industry professionals to make informed decisions.

Overview of Split-Core Current Transformer

A split-core current transformer is a type of current measurement device designed for easy installation around existing conductors without interrupting the power supply. Its defining feature is the split in the magnetic core, which allows the device to open and clamp around a live conductor. This non-intrusive design makes it highly convenient for retrofitting electrical systems.

Key features of split-core current transformer include:

• Non-intrusive installation: Can be installed without disconnecting the conductor.
• Wide current measurement range: Capable of handling both low and high current values.
• Compatibility with metering systems: Often used with energy meters, protective relays, and monitoring systems.
• Robust mechanical design: Designed for long-term reliability in industrial and commercial settings.

Table 1 illustrates typical technical characteristics of a split-core current transformer:

Overview of Rogowski Coil

The Rogowski coil is a flexible, air-cored coil used to measure alternating currents. Unlike the split-core current transformer, it does not rely on a magnetic core. Instead, it detects current through the voltage induced in a coil that encircles the conductor. Its inherent flexibility allows it to measure currents in conductors of varying shapes and sizes.

Key features of Rogowski coil include:

• High linearity: Maintains consistent accuracy over a wide current range.
• Lightweight and flexible: Can be wrapped around large or irregular conductors.
• Wide bandwidth: Suitable for high-frequency or transient current measurements.
• Safety advantage: The absence of a magnetic core eliminates core saturation issues.

Table 2 provides a comparison of Rogowski coil typical parameters:

Construction Differences

The split-core current transformer features a magnetic core, typically made from silicon steel or nanocrystalline material, and a secondary winding that produces a current proportional to the primary current. The split design allows the core to open and enclose a conductor without disconnecting it.

In contrast, the Rogowski coil uses a uniform, air-cored coil without magnetic material. Its construction emphasizes flexibility and uniform winding, with a focus on minimizing induced errors caused by conductor misalignment. Unlike split-core devices, Rogowski coils do not saturate and maintain linear response over a wide dynamic range.

Working Principle Comparison

The working principle of a split-core current transformer relies on magnetic induction. The primary current generates a magnetic flux in the core, which induces a proportional current in the secondary winding. This current can then be measured by meters or relays. Saturation of the core under high currents is a critical factor that can affect measurement accuracy.

The Rogowski coil, on the other hand, measures rate of change of current (di/dt) through electromagnetic induction in a coil. Because it is air-cored, the device does not experience magnetic saturation. To obtain an accurate current reading, the output signal is passed through an integration circuit. This distinction makes Rogowski coils suitable for high-frequency transients and harmonic detection, while split-core current transformers are often preferred for steady-state and metering applications.

Installation Considerations

Split-core current transformer installation is straightforward, as it can clamp around an existing conductor. Key considerations include ensuring proper core closure, correct secondary wiring, and adherence to the rated current and burden specifications. Improper installation can result in measurement errors and safety risks.

Rogowski coils offer exceptional installation flexibility. Their lightweight and bendable structure allows wrapping around large busbars or irregular conductors. Since the coil is air-cored, installation orientation has less effect on accuracy, though consistent positioning enhances measurement reliability.

Accuracy and Performance Comparison

While both devices provide reliable current measurements, differences in accuracy and performance are noteworthy:

• Split-core current transformer: Highly accurate for steady-state AC currents. Accuracy can degrade at low currents or when the core experiences saturation.
• Rogowski coil: Offers consistent linearity across a wide current range and excels in measuring transient currents and harmonics. However, signal integration is required to obtain absolute current readings, which may introduce minor phase errors.

Applications Comparison

Split-core current transformer is commonly used in:

• Energy metering systems
• Protective relays for overcurrent detection
• Industrial load monitoring
• Building energy management systems

Rogowski coils are preferred for:

• Transient current measurement in high-voltage systems
• Power quality analysis and harmonic monitoring
• Large conductor or busbar current measurement
• Laboratory and research applications

Advantages and Limitations

The choice between a split-core current transformer and a Rogowski coil depends on the application scenario:

Split-core current transformer advantages:

• Reliable for steady-state AC measurement
• Easy retrofitting for existing systems
• Compatible with standard metering equipment

Limitations:

• Core saturation can occur at high currents
• Heavier and less flexible than Rogowski coils

Rogowski coil advantages:

• Lightweight and highly flexible
• Excellent linearity and transient measurement capability
• No core saturation

Limitations:

• Requires integration electronics
• Slightly lower accuracy at very low currents

Considerations for Procurement and Selection

When selecting a split-core current transformer, buyers should consider:

• Rated primary and secondary current
• Accuracy class and burden specifications
• Environmental conditions (temperature, humidity, installation location)
• Compliance with relevant safety standards

For Rogowski coils, considerations include:

• Coil size and flexibility
• Bandwidth requirements
• Signal integration and processing equipment
• Application type (transient vs. steady-state measurement)

Conclusion

While both split-core current transformer and Rogowski coil serve the fundamental purpose of measuring electrical current, their construction, working principles, installation methods, and performance characteristics differ significantly. Split-core current transformers excel in standard AC measurement and energy metering applications, offering ease of installation and high accuracy. In contrast, Rogowski coils provide flexibility, high linearity, and excellent transient measurement capabilities, making them suitable for specialized monitoring and power quality analysis.

Understanding these differences enables engineers, procurement professionals, and system integrators to select the most appropriate current sensing device for their specific industrial, commercial, or research requirements.

FAQ

Q1: Can a split-core current transformer measure DC current?
A1: No, a split-core current transformer is designed for AC current measurement. For DC current, other sensing technologies like Hall-effect sensors are required.

Q2: Is installation of a split-core current transformer difficult?
A2: Installation is generally straightforward, as it can clamp around existing conductors without disconnecting them. Ensuring proper core closure is critical.

Q3: Can Rogowski coils replace split-core current transformers in all applications?
A3: Not always. Rogowski coils excel in transient and harmonic measurement, but split-core current transformers may be preferred for standard metering due to their simplicity and compatibility with existing equipment.

Q4: What maintenance is required for split-core current transformers?
A4: Regular inspection for core integrity, secure connections, and environmental protection is recommended. Maintenance requirements are generally minimal.

Q5: Are there accuracy differences between split-core and solid-core current transformers?
A5: Yes. Split-core transformers may have slightly lower accuracy than solid-core versions due to potential air gaps in the magnetic core, but they offer installation convenience.

References

1. IEEE Standard C57.13 – Standard Requirements for Instrument Transformers.
2. Krause, P. C., Wasynczuk, O., Sudhoff, S. D., Analysis of Electric Machinery and Drive Systems, 4th Edition.
3. H. Dommel, Power System Harmonics: Fundamentals, Analysis, and Filter Design.