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Keeping Tabs on Power Lines
November 3, 2014   
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A team of researchers led by Prof. Andrzej Napieralski from the £ód¼ University of Technology in central Poland has developed computer software for the electrothermal analysis of medium- and high-voltage power lines, including underground oil-cooled power cables, that is being used in the United States and Canada.

It all started with a major power grid failure in the United States in August 2003, the biggest in North American history. The blackout in the East Coast had a lot in common with an earlier failure in July 1996. Both incidents were triggered by a short circuit affecting power lines. The failures exposed the inadequacy of the system, in which the permissible load on the power lines had not been specified.

If certain parameters are exceeded, for example, if there is an increased flow of electricity or higher air temperature, which consequently raises the temperature of the soil, underground cables become overheated and damaged. In extreme cases this can cause them to melt or leak. A leak of thousands of gallons of coolant oil is hazardous to the environment. The main problem is to locate the leak as soon as possible. In large cities it is often difficult to dig out long and deep excavations.

In 2003, a team of researchers from the £ód¼ University of Technology Department of Microelectronics and Computer Science (DMCS), which is headed by Napieralski, went to Canada at the invitation of George J. Anders, Ph.D., a Canadian academic and engineer with ties to the £ód¼ university who was principal engineer at the Ontario Hydro Technologies company at the time. Anders received a master’s degree in electrical engineering from the £ód¼ University of Technology in 1973. Today he is a professor at the university and an expert in the development of power cable calculation methods and application of advanced techniques in power system analysis.

The £ód¼ team consisted of computer scientists, electronic engineers and academics specialized in artificial intelligence. The main aim of the project was to predict possible failures on the basis of temperature and pressure measurements involving the cables, using a number of sensors. The calculations of the £ód¼ scientists took in factors including the temperature of internal components and the temperature of the oil used in the cooling system. The calculations made it possible to predict just how much load can be put on power lines before they overheat within a certain period of time. Another factor taken into account was that cables age while being used, losing the required parameters due to high load, seasonal changes in ambient temperature and changes in the humidity of sand in the case of underground cables. Such installations are expensive and their owners are keen to make sure they work flawlessly for as long as possible. It was therefore necessary to calculate how the process of wear would occur to predict when it will be necessary to replace a specific component.

Mariusz Orlikowski, D.Sc., (who was later singled out for praise by Ontario Hydro Technologies) handled data management, and Mariusz Zubert, D.Sc., handled the calculations stage of the project. On the basis of sensor measurements, Zubert performed calculations of the thermal parameters of the cables, making it possible to check to what extent it was possible to increase the flow of electricity at a specific time without causing the grid to overheat.

“My job was to predict the state of the cables and designate their maximum short- and long-term load—from 10-15 minutes to infinity,” says Zubert. “It was also necessary to find out which lines could transfer more power to relieve other cables. Another important thing was optimization of the entire power grid in Canada, which means checking the weakest points in the system to guarantee its efficiency and continuity of operation.”

Orlikowski said, “The coolant leak detector systems that our team found in the power grid were inadequate. Everything would’ve been much simpler if we had been able use to sensors of our own design. Unfortunately, we had to use those that were already there. The entire pump system was out of sync and it was difficult to control it. It was also difficult to detect that the system had gone haywire. There was so much oil in the cooling system that it took a long time to notice any difference in the pressure of the coolant pointing to a leak.”

The programs developed by the £ód¼ team proved successful. They have been used in cities including Ontario and Toronto as well as New York for several years now.

Danuta K. Gruszczyńska
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