Outstanding achievement for ABB's Corporate Research
Blackouts, such as the ones that occurred during the summer of 2003, not only in the United States and Canada, but also in Italy, Sweden, Denmark and London, and which left millions of people suddenly standing in the dark and stuck in subway systems, have demonstrated that high-voltage networks must be monitored more reliably and efficiently. ABB's new fiber-optic current sensor could play a key role in addressing this need. The innovative product has impressed quite a number of international experts. Besides being one of the top five nominees for the Hermes Award 2005, the fiber-optic current sensor has also been nominated for the renowned Swiss Technology Award as one of the four best products in 2005. As a result, the innovative product, which was developed by ABB's Corporate Research Center in Baden, Switzerland, will be shown at the Swiss Technology Award organization's booth at Hannover Messe (Hall 2, Booth A28) and at the booth of the Hermes Award (Hall 2, Booth D16).
Electrical power is transmitted and distributed via high-voltage substations, and in these installations, current must be measured continuously and around-the-clock. The conventional way to do this is to use so-called instrument current transformers, whose life span is typically 30 to 40 years. Particularly in a deregulated electricity market, where energy flows (including those that were not planned) across borders must be measured at the countless interfaces between the market players, there is a need for more precise and more reliable current measurement. The measurement is required for revenue metering of power, as well as control and protection of the high-voltage systems, and in the future, secondary digital electronic systems will play an increasingly important role in this regard.
The fiber-optic current sensor developed by ABB's researchers meets these needs. The current measurement concept is contact-free. The device relies on the Faraday effect, whereby the magnetic field influences the speed of light in an optical fiber. In order to measure the current, light waves are transmitted through this optical fiber. One or more turns of the fiber are wound around the current conductor. The light waves travel at different speeds in the magnetic field generated by the current and therefore require different amounts of time to travel through the optical fiber. The difference in propagation time becomes larger with increasing current and with a higher number of turns of the optical fiber around the electrical conductor. The phase displacement between the light waves is measured after they have traveled through the optical fiber. Although the difference is only a fraction of the wavelength of the light (820 nanometers), it can be very precisely determined.
Electrical power is transmitted and distributed via high-voltage substations, and in these installations, current must be measured continuously and around-the-clock. The conventional way to do this is to use so-called instrument current transformers, whose life span is typically 30 to 40 years. Particularly in a deregulated electricity market, where energy flows (including those that were not planned) across borders must be measured at the countless interfaces between the market players, there is a need for more precise and more reliable current measurement. The measurement is required for revenue metering of power, as well as control and protection of the high-voltage systems, and in the future, secondary digital electronic systems will play an increasingly important role in this regard.
The fiber-optic current sensor developed by ABB's researchers meets these needs. The current measurement concept is contact-free. The device relies on the Faraday effect, whereby the magnetic field influences the speed of light in an optical fiber. In order to measure the current, light waves are transmitted through this optical fiber. One or more turns of the fiber are wound around the current conductor. The light waves travel at different speeds in the magnetic field generated by the current and therefore require different amounts of time to travel through the optical fiber. The difference in propagation time becomes larger with increasing current and with a higher number of turns of the optical fiber around the electrical conductor. The phase displacement between the light waves is measured after they have traveled through the optical fiber. Although the difference is only a fraction of the wavelength of the light (820 nanometers), it can be very precisely determined.
- An extremely thin glass fiber replaces hundreds or even thousands of kilograms of copper, iron and insulating material. Time-consuming and costly installation is eliminated.
- The measuring range is significantly wider and the precision significantly better, particularly for high currents.
- In contrast to conventional instrument transformers, permanent damage because of excessively high overcurrents is not possible; neither is there any oil to pollute the environment.
- The high bandwidth makes it possible to quickly react to short-circuit currents and protect the system. Even the "quality" of the current can be derived (power quality monitoring).
- Because secondary electronics (substation control, protective devices etc.) is connected via a fiber-optic link, it is protected against damage or electromagnetic interference from high-voltage effects.
- The digital signal from the fiber-optic sensor is directly compatible with future digital secondary electronics.
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