Researchers from Indian Institute of Technology (IIT) Kanpur have come up with an innovation that can help protect power grids against sudden, unexpected current surges. An innovative variation of the superconducting fault current limiter (SFCL), this smart SFCL not only shields the grid from large current surges and consequent fire accidents, it can also sense when the current surges will happen and warn the system about it.
Power grids need protection from sudden surges in the current (fault current) that arise due to short-circuits, sudden overdrawing of power or excess power generated due to a falling demand. These surges cause heating of the wires and perhaps melting and consequent short-circuits and fire accidents. Earlier this used to be controlled by using circuit breakers, which would cut off the current in the event of a surge. These suffered from the limitation that if the response time to the current surge was too large, they would fail to be effective. Also, once the circuit was broken to avert the accident, the switch had to be manually turned on once again, and this could lead to longer power cuts.
Using superconductors
In the last decade, mainly in developed countries, a new way to tackle this situation is being explored – using superconducting fault current limiters (SFCL).
This device uses a superconductor, which allows a dissipationless passage of current under normal circumstances, as it offers zero resistance to current flow in the superconducting state. However, if the current flowing through it increases beyond a threshold value, as during a fault, its resistance increases sharply. “The operation of a SFCL is very rapid and automatic. Once the fault current reduces and the current flow returns to below the threshold value, the resistance of the SFCL also automatically goes down to zero,” explains Satyajit Banerjee, Professor from the Department of Physics at IIT Kanpur and an expert on superconductivity.
Over a period of about three years, Prof. Banerjee and his PhD scholars have developed this “smart” SFCL device which deploys an array of Hall sensors around a basic SFCL. The array of Hall sensors placed around the SFCL constantly “measure and monitor as well as map” the current flowing inside the superconductor.
“This sensor circuitry we have incorporated also serves the purpose of monitoring the current flow in the SFCL, which, in turn can be used to detect the initial stages of the current surge during the appearance of a fault,” says Prof Banerjee. He further explains that this can help the detection of a fault situation even while it is developing and therefore, before the large surge fully sets in, one can take pre-emptive action to intentionally switch the SFCL into a high resistive state and limit the increase in fault current and also divert the excess current through a lower resistance path.
There is also another aspect of smartness to the device. All SFCLs are susceptible to internal thermal instabilities. The prototype they have developed is able to sense this too. This is an added advantage.
Lower cost
The imported SFCL devices cost around a million Euros. The prototype “smart” SFCL developed by Prof. Banerjee’s group cuts this cost by 50%-60%. However, he is not at the moment thinking of taking this to the industry. “Scaling up of these technologies cannot be a one man show… Such a thing can happen only with a match of efforts from the Industry and innovations by the academia. The future of the innovation is that it has to be implemented with current state-of-the-art developments in SFCLs to make them more powerful,” he opines.
Handling larger currents
Some interesting further innovations that his group is aiming for are in developing high temperature superconducting materials which have larger critical currents, as this will allow the SFCL to operate up to higher currents.
“Another important area in this direction is to use our sensor array to enhance its sensitivity further so that we can pinpoint the location of a instability developing in the superconductor in space and time and study its evolution,” says Prof. Banerjee. Though this is a challenging area and a “non-trivial task,” it is absolutely essential in order to develop more reliable, intelligent and efficient SFCLs.
