Publish Time: 2026-08-15 Origin: Jiangyin Spark Electronic Technology Co., Ltd.
Fault Passage Indicators (FPIs) are widely used in power distribution networks to help locate faults and reduce the time required to identify a faulty section of a feeder. Current sensing is an important part of many FPI designs, and a Rogowski coil can provide a practical solution where flexible installation, electrical isolation and measurement of high AC currents are required.
However, not every Rogowski coil is suitable for a fault indicator.
When selecting a Rogowski coil for a Fault Passage Indicator, engineers should consider the current range, output signal, coil size, frequency, accuracy, environmental protection and—most importantly—whether the FPI has its own signal-processing circuit.
A Rogowski coil is a flexible current sensor installed around a conductor. Because it does not require a conventional magnetic core, it can be opened and installed around an existing cable without disconnecting the conductor.
For fault passage indicator applications, this provides several advantages:
Easy installation around existing cables
No need to disconnect the primary conductor
Measurement of high AC and transient currents
Good electrical isolation
Lightweight and flexible construction
Different coil diameters can be designed for different cable sizes
Suitable for distribution network monitoring
These characteristics make Rogowski coils particularly useful when a conventional solid-core current transformer is difficult to install.
The first step is to understand the normal operating current and the expected fault current.
For example, an FPI may need to monitor normal feeder current while also detecting a significant increase in current during a short-circuit or earth-fault condition.
A Rogowski coil should therefore be selected according to both:
Normal operating current
and
maximum fault current
For one common configuration, a 1000A/100mV Rogowski coil can be used when the monitoring circuit is designed for a 100mV signal at the rated current.
Other current ranges and output levels can be selected according to the FPI input circuit.
This is one of the most important points when choosing a Rogowski coil for an FPI.
Rogowski coil solutions can be supplied with different output configurations, such as:
mV output
333mV output
1A or 5A output
0–5V output
4–20mA output
Digital communication through additional electronics
The correct choice depends on the input of the fault indicator.
For example, if the FPI electronics are designed to receive a low-level voltage signal, a 100mV or 333mV Rogowski coil may be appropriate.
If the monitoring equipment requires a standard 5A current input, additional signal conditioning or an integrator/transducer may be required.
Therefore, the output of the Rogowski coil should always be matched to the FPI input circuit rather than selected only according to the primary current rating.
This is a common question in fault indicator projects.
A Rogowski coil naturally produces a signal proportional to the rate of change of current. In many measurement systems, an integrator is used to reconstruct the current waveform and provide a standardized output.
However, an external integrator is not always necessary.
Some Fault Passage Indicators already contain their own signal-processing, integration or current-detection circuitry. In this case, the manufacturer may require a Rogowski coil without an external integrator.
This type of configuration can simplify the sensor assembly and allow the FPI manufacturer to process the coil signal directly inside its own electronics.
Before selecting the sensor, confirm:
Does the FPI have an internal integrator?
What input voltage does the circuit require?
What is the input impedance?
What current level should correspond to the rated output?
What frequency range must be measured?
These questions are more important than simply choosing a Rogowski coil based on current rating.
The Rogowski coil must physically fit around the conductor.
For retrofit installations, measure the outside diameter of the cable or the space available around the conductor before selecting the coil.
The coil opening should provide sufficient installation clearance without being unnecessarily large.
Depending on the application, Rogowski coils can be manufactured with different:
Coil diameters
Coil lengths
Lead wire lengths
Connector types
Output cable configurations
For OEM Fault Passage Indicator projects, these mechanical dimensions can often be customized to match the enclosure and installation method.
Fault indication and precision energy metering have different measurement requirements.
For an FPI, the key requirement may be reliable detection of a current threshold rather than revenue-grade energy measurement. Nevertheless, stable accuracy and repeatability are important because the sensor signal directly affects the fault-detection algorithm.
For example, the Spark Electronic RCT-1000A/100mV Rogowski coil can be supplied with accuracy up to ±1%, depending on the required configuration.
When evaluating a Rogowski coil, engineers should consider:
Rated current accuracy
Linearity
Phase characteristics
Temperature drift
Repeatability
Frequency response
The actual requirements should be determined by the FPI detection circuit and algorithm.
Fault indicators are often installed in distribution networks where sensors may be exposed to humidity, dust, temperature changes and other environmental conditions.
For outdoor applications, check the environmental protection of the Rogowski coil and cable assembly.
Important considerations include:
IP protection level
Operating temperature
Storage temperature
Cable insulation
UV resistance when required
Mechanical durability
Long-term stability
For outdoor fault indicator applications, an IP67 Rogowski coil can provide additional protection against dust and temporary water exposure.
For commercial FPI products, certification can be an important part of component selection.
If the final equipment is intended for North American or other regulated markets, engineers should check whether the sensor has relevant safety certification and whether that certification is applicable to the final system design.
Spark Electronic offers UL certified Rogowski coil options for current sensing applications.
Certification requirements should always be confirmed according to the final equipment, installation environment and applicable standard.
One possible FPI sensor configuration is:
Parameter | Example Specification |
|---|---|
Sensor Type | Flexible Rogowski Coil |
Application | Fault Passage Indicator (FPI) |
Rated Current | 1000A AC |
Rated Output | 100mV |
Accuracy | Up to ±1% |
Integrator | Without external integrator |
Installation | Split / flexible installation |
Environmental Protection | IP67 option |
Certification | UL certified option |
Customization | Coil size, lead wire, current and output |
This configuration can be suitable for a Fault Passage Indicator whose electronics are designed to process the Rogowski coil signal internally.
It should not be assumed that 1000A/100mV is suitable for every FPI. The sensor must be matched to the electrical characteristics of the customer's input circuit.
Before requesting a sample or quotation, providing the following information can make sensor selection much faster:
Normal operating current
Maximum fault current
Required output signal
FPI input specification
Whether an internal integrator is already included
Cable or conductor diameter
Required Rogowski coil diameter
Lead wire length
Operating temperature
Indoor or outdoor installation
Required IP rating
Certification requirements
For a new FPI design, providing the input circuit requirements can also help the sensor manufacturer recommend a suitable coil configuration.
Yes. Rogowski coils can be used as current sensors in Fault Passage Indicators, particularly where flexible installation and high-current sensing are required. The coil output must be compatible with the FPI signal-processing circuit.
Not always. If the FPI already includes the required integration or signal-processing circuit, a Rogowski coil without an external integrator may be used.
It can be suitable when the FPI input circuit is designed for this current-to-output relationship. The normal operating current, expected fault current and FPI input characteristics should be checked before selection.
Yes. For OEM projects, coil diameter, lead wire length, current rating, output and connector configuration can be customized according to the installation and electrical requirements.
The basic sensing principle can be the same, but an FPI application may have different requirements for output signal, fault-current range, signal processing, environmental protection, dimensions and installation. The sensor should therefore be selected according to the complete FPI circuit rather than only its rated current.
Choosing a Rogowski coil for a Fault Passage Indicator requires more than selecting a current rating.
The engineer should match the Rogowski coil to the fault current range, FPI input signal, integrator design, conductor size, installation environment and certification requirements.
For FPI manufacturers that already have their own signal-processing circuit, a Rogowski coil without an external integrator can be an effective solution.
Jiangyin Spark Electronic Technology Co., Ltd. manufactures flexible Rogowski coils for current measurement and fault monitoring applications, including UL certified 1000A/100mV Rogowski coil options for Fault Passage Indicators. OEM options are available for different current ratings, output signals, coil dimensions and lead wire lengths.
For model selection, provide your current range, required output, FPI input specification and conductor size so that a suitable Rogowski coil configuration can be evaluated.