Optical current transformers are proven and ready for use in a variety of global applications, ensuring long-term sustainability and no environmental compromises. Oil and SF6 are not used as insulating media in optical current transformers, nor do they contain any electronic components. The Faraday effect is the foundation of optical current transformers. A low power optical signal is the output, and it is subsequently sent to a merging unit for protocol adaptation. Customers can measure a variety of grid signals that are often undetectable by traditional instrument transformers thanks to the usage of non-standard instrument transformers in AIS switchgear. Additionally, the communication protocols provide digitalized grid information, control functions, protection, and measurement.
What is Optical Current Transformer?
One kind of sensor used to measure electrical current is an
optical current transformer. OCTs, or optical current transformers, measure
current using optical fibers. Optical current transformers work by employing a
fiber-optic sensing device to detect the magnetic field produced by the current
passing through a wire. A coil of optical fiber that is wound around the
conductor makes up the sensor element. A photodetector detects the tiny
rotation of the plane of polarization of the light that is passed through the
fiber due to the magnetic field created by the current. By examining the
observed signal's phase shift and amplitude, one can ascertain the current's
magnitude. Fiber optic and magnetic optical current transformers are the two
main varieties of optical current transformers. Higher precision, a larger
bandwidth, less magnetic interference, a smaller size, and less maintenance are
all benefits of optical current transformers. Optical current transformers are
finding increasing use in the fields of renewable energy and power generation,
transmission, and distribution
Working Principle of OCT
The measurement of polarization rotation caused by the Faraday effect is the fundamental idea behind optical current transformers, or OCTs. The rotation of light's polarization state, β, as it travels through a magnetic field, B, caused by an electrical current, is known as the Faraday effect. The magnetic field and, thus, the polarization rotation increase with the electric current. Compared to conventional current sensing technologies, OCTs have the following advantages: the sensor element is naturally decoupled from the voltage line; there is very little electrical interference on the signal line; they provide incredibly fast response times with high measurement accuracy; they are smaller and lighter than existing technologies; and unlike oil-filled electrical insulation towers, they do not explode during catastrophic failure.
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| Representation of rotation of light polarization Source: https://fibercore.humaneticsgroup.com/perspectives/fiber-optic-current-sensors-and-optical-current-transformers |
Types of Fiber used in OCT
Spun LoBi Fiber: In order to average out the natural
birefringence created throughout the fiber production procedures, a Spun LoBi
fiber is a Single-Mode (SM) fiber that is spun during the fiber drawing stage. The
fiber experiences cumulative stress as the coil diameter is decreased or the
number of coils is increased, which raises the total birefringence and reduces
the sensitivity of the measurements. Consequently, low sensitivity OCTs with a
wide coil diameter and a comparatively small number of coils are usually
equipped with spun LoBi fibers.
Spun HiBi Fiber: Spun HiBi fiber is recommended for high sensitivity OCTs. The Polarization Maintaining (PM) axis of this fiber, which is created by Fibercore's "Bow-Tie" structure, sets it apart from the Spun LoBi fiber. A fiber can be engineered to be sensitive to the Faraday effect while overcoming the influence of bend-induced stress caused by the coiling process by carefully balancing the spin pitch of the fiber with a precisely controlled amount of birefringence. Because Spun HiBi fiber may be utilized in longer lengths than Spun LoBi fiber, more coils of fiber with smaller coil widths can be employed, increasing sensitivity Additionally, the fiber's HiBi nature lessens the impact of vibration and temperature.
Optical Current Transformers Product Design
- Useful for voltage levels between 72 and 800 kV
- No sacrifices on the environment, and no gas taxation
- Primary and secondary side galvanic separation
- Using a single fiber-optic cable rather than multiple large-cross-section copper wires
- Clean air creates internal insulation
- Lowest training, transportation, installation, operation, reporting, and recycling requirements for F-gas-free insulation
- There is no chance of C-gas breakdown. Recycling of gas is not necessary.
Characteristics of OCT
- No restriction on ambient temperature
- filled with nitrogen that has been squeezed just above room pressure to prevent moisture or other things from entering. Glass ring sensors in an aluminum housing
- Composite-material insulators that are resistant to earthquake, tensile, and short-circuit mechanical stresses
- A box for connecting a TOCT to the fiber optic cables of the station
- A light source, photodetectors, and signal processing are all included in this signal processing and merging unit. It has up to three separate measuring channels.
Why OCTs Better Than Conventional Current Transformers?
For complicated and dispersed power systems to operate and be protected,
current must be measured accurately and promptly. The performance of the
protective system may be impacted by the bandwidth, accuracy, and immunity to
electromagnetic interference limits of conventional magnetic CTs. Compared to
magnetic CTs, OCTs provide a number of benefits, such as increased bandwidth,
improved accuracy, and immunity to electromagnetic interference. Because of
these characteristics, OCTs are perfect for power system protection
applications, where precise and quick current monitoring is necessary to
identify problems and activate protective devices.
OCTs are applicable not only to power systems but also to
industries including industrial automation, renewable energy, and
transportation. To ensure safe and effective charging, OCTs, for instance, can
be used at electric vehicle charging stations to monitor the current supplied
to the vehicle. OCTs can be used to monitor the current produced by wind
turbines or solar panels in renewable energy systems, allowing for improved
power output control and management. The usage of OCTs and the replacement of
magnetic CTs in many applications are predicted to increase as a result of
ongoing technological advancements that lower production costs.
Conclusion
The Faraday effect, which alters the polarization angle of light when it passes through a magnetic field, is the foundation of optical current transformers. In terms of accuracy range (which is practically infinite), safety (no chance of explosive failures), environmental protection (no SF6), and complete passivity, optical current transformers are exceptional. Based on state-of-the-art optical sensing technology, optical current transformers are a ground-breaking substitute for traditional current transformers, offering a sophisticated solution for protection and measurement applications.
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