Sensor accuracy has to improve to prevent electrical grid overload
The sensors introduce errors when assessing current through iron conductors and it is crucial to correct this flaw so that operators of the electrical grid can correctly respond to threats to the system.
The researchers show how a difference in a conductor’s magnetic permeability, the degree of material’s magnetization response in a magnetic field, affects the precision of new yokeless current sensors. They also provide recommendations for improving sensor accuracy.
“If you have a grid at the edge of capacity, you have to be careful to monitor all the transients,” said researcher Pavel Ripka. “Every day you get a lot of these small surges within a big power grid, and sometimes it is difficult to interpret them. If it is something really serious, you should switch off parts of the grid to prevent catastrophic damage, but if it’s a short transient which will finish fast there is no need to disconnect the grid. It’s a risky business to distinguish between these events, because if you underestimate the danger then parts of the distribution installations can be damaged causing serious blackouts. But if you overestimate and disconnect, it is a problem because connecting these grids back together is quite complicated,” he said.
Yokeless current sensors are increasingly popular because of their low cost and compact size. These sensors are good for assessing currents in nonmagnetic conductors such as copper and aluminium. However, ground conductors are usually iron due to its mechanical strength, and iron has a high magnetic permeability. The study has shown that not taking into account the magnetic permeability of a conductor distorts the accuracy of a reading with a yokeless sensor.
Ripka and his team matched experimental measurements with theoretical simulations to highlight the difference in yokeless sensor readings between nonmagnetic and magnetic conductors.
“We can show how to design yokeless current sensors so that they are not so susceptible to this type of error,” he said. “This study is just a small reminder to make [engineers] design sensors safely.”
Ripka’s group is starting to take long-term readings at power stations, comparing results to commercial uncalibrated sensors and Ripka sees future cooperating with geophysicists to correlate ground currents and geomagnetic activity, to better understand how these currents are distributed within the earth and even predict future disruptions to the grid.
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