Contents of this article:

1. What is a fiber optic current sensor
2. Working principle of optical fiber current sensor
3. Application scenarios of optical fiber current sensors
4. Advantages and disadvantages of optical fiber current sensor and its characteristics
4.1 Advantages of optical fiber current sensor
4.2 Disadvantages of optical fiber current sensor
4.3 Characteristics of optical fiber current sensor
5. How to choose a suitable optical fiber current sensor
6. Conclusion

As a new sensing technology, optical fiber current sensor has been widely used in high-voltage transmission lines, substations and other power facilities. It not only has the unique advantages that the traditional electromagnetic current transformer does not have, but also provides a strong technical support for the development of smart grid. However, you may be curious about exactly how fiber optic current sensors work.

Next, let's take a look at the working principle of fiber optic current sensors and the characteristics of different types of fiber optic current sensors. Based on the Faraday effect, when linearly polarized light passes through an optical fiber placed in a magnetic field, the polarization plane of the light rotates, a phenomenon that can be used to indirectly measure the current flowing through a conductor. This non-contact measurement method not only improves safety, but also provides higher accuracy and a wider range of applications. We will also detail several common types of fiber optic current sensors, such as all-fiber and magneto-optical glass, and analyze the advantages and application scenarios of each type. Through this content, you will be able to better understand how fiber optic current sensors are revolutionizing power monitoring technology and laying a solid foundation for the future development of smart grids.

1. What is a fiber optic current sensor

Optical fiber current sensor (FOCS) is a device that uses optical fiber technology to measure current. It is based on the Faraday magneto-optical effect, a phenomenon in which the plane of polarization of linearly polarized light rotates when it passes through certain materials (such as magneto-optical crystals) placed in a magnetic field. This Angle of rotation is proportional to the strength of the magnetic field passing through the material.

Figure 1: Optical fiber current sensor (figure from baike.baidu)

Optical fiber current sensor is composed of light source, optical fiber, magneto-optical material, photodetector and electronic circuit. The light source is responsible for providing a stable optical signal, while the optical fiber undertakes the task of transmitting this optical signal, and its specific part is also exposed to the magnetic field generated by the current being measured. Magneto-optical materials generally use specially treated optical fibers or magneto-optical crystals and are placed near the current to be measured so that the magnetic field changes generated by the current can be sensed. Subsequently, the photodetector converts the received light signal into an electrical signal; Finally, these electrical signals are processed by electronic circuits to calculate the specific current value.

2. Working principle of optical fiber current sensor

Fiber optic current sensors (FOCS) work based on the Faraday magneto-optical effect, which refers to the fact that when linearly polarized light passes through a specific material placed in a magnetic field, its polarization plane rotates at an Angle proportional to the strength of the magnetic field. In FOCS, light emitted by a stable light source such as a laser diode or LED first passes through a polarizer and becomes linearly polarized. This linearly polarized light is then directed to the core of the sensor through a section of fiber - usually a special magneto-optical crystal or magneto-optical fiber. When a current flows through a nearby conductor, a magnetic field is generated, which passes through the magneto-optical material and rotates the linearly polarized light through the material in the direction of polarization according to the Faraday effect, the Angle of rotation is proportional to the product of the magnetic field strength and the length of the material.

Figure 2: How the optical fiber current sensor works

After passing through the magneto-optical material, the light continues to travel along the fiber to the photodetector, which measures the change in the polarization direction of the light and converts it into an electrical signal. The electronic circuit then processes these electrical signals, converts them into digital signals, and calculates the actual current value. Finally, the resulting current value can be displayed, recorded, or used for further data analysis and control. Due to their high insulation, electromagnetic interference resistance, and wide operating temperature range, fiber optic current sensors are particularly suitable for power system monitoring, motor operation status monitoring, and a variety of applications requiring accurate and safe current measurement.

3. Application scenarios of optical fiber current sensors

Figure 3: Optical fiber current sensor in China Electric Power Research Institute (Wuhan) isolation knife opening and closing test site (figure from YINHE ELECTRLC)

Power system monitoring: FOCS deployed in power plants, substations and other places can accurately obtain current information at each node in real time, helping to improve the efficiency of the entire network operation.

Rail transit: applied to the traction power supply system of subway vehicles to help staff find abnormal situations in time and take corresponding measures to ensure driving safety.

New energy field: For example, wind power stations are used to monitor blade speed and generator output power and other parameters to help efficient use of clean energy.

Scientific research education: As one of the teaching experiment equipment, let students intuitively understand the photoelectric conversion principle and related physical concepts; It also plays an important role in scientific research projects.

4. Advantages and disadvantages of optical fiber current sensor and its characteristics

Fiber optic current sensors (FOCS) combine several technical advantages, but also have some limitations. By comprehensively considering its advantages, disadvantages and characteristics, it is possible to better evaluate whether fiber optic current sensors meet the needs of specific applications and make appropriate choices.

The following are the main advantages, disadvantages and features of FOCS:

Advantages of fiber optic current sensors

High insulation performance: Due to the use of non-conductive optical fiber as the sensing medium, FOCS is able to operate safely in high voltage environments without the need for additional insulation measures.

Anti-electromagnetic interference: The optical fiber itself is not sensitive to electromagnetic fields, so FOCS can effectively resist external electromagnetic interference to ensure the accuracy and reliability of measurement results.

Wide temperature range: FOCS is capable of stable operation over a wide temperature range and is suitable for applications under extreme temperature conditions.

Small size and light weight: The compact design makes these sensors easy to install in space-constrained locations and easy to carry and deploy.

Contactless measurement: Measurements can be made without direct contact with the circuit under test, reducing maintenance costs and potential safety risks.

Long-term stability: With no moving parts, FOCS exhibits good long-term stability, reducing maintenance requirements and improving system reliability and service life.

No saturation phenomenon: Even under extreme conditions, FOCS will not saturated the core like traditional electromagnetic current transformers, ensuring long-term reliability and accuracy.

Wide dynamic range: able to cover a wide range of current from microamps to thousands of amps to meet the needs of different application scenarios.

Environmental protection and energy saving: do not need to use oil or other cooling media, reduce maintenance costs, but also reduce the risk of environmental pollution, no fire hazards.

Fast response time: Some advanced models of FOCS have extremely fast response times and are suitable for applications that require real-time monitoring, such as protection systems.

Remote Monitoring and data logging: Many modern FOCS feature data logging and remote monitoring to facilitate data analysis and management.

Disadvantages of fiber optic current sensors

Higher cost: FOCS may have a higher initial investment cost than traditional electrical or electronic current sensors.

Technical complexity: The design, manufacturing and calibration processes are relatively complex and require a high level of technology to ensure accuracy and reliability.

High signal processing requirements: In order to accurately convert optical signals to electrical signals and finally obtain current values, complex signal processing algorithms and techniques are required.

Sensitivity issues: At low current levels, its sensitivity may not be as good as some traditional sensors.

Temperature dependence: Despite operating over a wide temperature range, temperature changes can affect measurement accuracy, especially under extreme conditions.

Characteristics of optical fiber current sensor

Based on the Faraday effect: Using the Faraday magneto-optical effect, when linearly polarized light passes through an optical fiber placed in a magnetic field, the polarization plane of the light will rotate, which is used to indirectly measure the current flowing through the conductor.

Non-contact measurement: No direct contact with the circuit under test is required, increasing safety and extending the range of applications.

High precision and resolution: Provides high precision and high resolution current measurements for a wide range of precision applications.

Strong adaptability: There are many types of FOCS (such as all-fiber type, magneto-optical glass type, etc.), you can choose the most suitable type according to different application needs.

Digital outputs: Many FOCS offer digital outputs for easy integration into modern control systems, supporting remote monitoring and data analysis.

5. How to choose a suitable optical fiber current sensor

During the selection process, a number of factors need to be considered to ensure that the selected sensor can meet the needs of the specific application.

Here are some of the key selection criteria and steps summarized by INFINITECH:

① Measurement range: Determine the required current measurement range. Different types of fiber optic current sensors are suitable for different current levels, ranging from a few milliamps to several thousand amps.

2 Accuracy and resolution: According to the application requirements to determine the required measurement accuracy and resolution. Some applications may require very high accuracy, while others may accept lower standards.

Response time: If you need to quickly detect current changes, then response time is an important consideration. Some applications such as protection systems may require extremely fast response times.

Temperature range: Considering the temperature conditions of the working environment, select a sensor that can work stably within the temperature range. Some sensors are designed for extreme temperature environments.

Installation method: Evaluate the space limitations of the installation location and the installation method (for example, whether contactless installation is required). Make sure the sensor is easy to install and does not interfere with existing electrical equipment.

Electromagnetic compatibility: In the presence of strong electromagnetic field interference in the environment, it is particularly important to choose a sensor with good anti-interference ability.

⑦ Cost-effectiveness: Balance performance requirements with budget constraints. While high-performance sensors are generally more expensive, reliability and low maintenance costs may lead to overall savings in the long term.

Manufacturer support: Consider the supplier's technical support, warranty policies and spare parts availability. A reliable supplier can provide timely help when problems arise.

Industry standards and certifications: Ensure that the selected sensors comply with the relevant international or national standards and have the necessary safety certifications.

⑩ Additional features: Some advanced models may include data logging, remote monitoring and other features, which may be beneficial for specific application scenarios.

In the actual selection process, it is recommended to first research the products on the market to understand the characteristics of different brands and models. At the same time, you can also consult a professional or contact the manufacturer for more detailed information about the product and technical specifications. Finally, if possible, it's a good idea to run a sample test to verify that the sensor really meets your specific needs.

6. Conclusion

In summary, optical fiber current sensor (FOCS), as an innovative measurement technology, has demonstrated its unique advantages in many fields such as power systems, rail transit and new energy. Based on the Faraday magneto-optical effect, this sensor enables contactless current measurement, which not only improves safety, but also provides higher accuracy and a wider range of applications. Although FOCS presents some challenges in terms of cost and technical complexity, its high insulation, resistance to electromagnetic interference and ability to adapt to extreme temperature environments make it ideal for many critical applications.