Aurora Versus Power Lines
The northern lights are pretty to look at, but we all know that every silver cloud has a cruddy lining. At least it does for the electrical engineer.
One problem is that intense electrical currents in the ionosphere accompany large auroral displays. Sometimes currents as large as a few hundred thousand amperes flow along the aurora, 60 miles above the earth's surface. As these currents wax and wane from minute to minute, they induce voltages in the conducting surface of the earth. The induced voltage can be as large as one volt per kilometer, about six-tenths of a volt per mile.
This voltage also appears in wires such as telegraph or electrical transmission lines which are grounded to earth at each end. The voltage appearing is proportional to the length of the line, hence a long line can acquire a large voltage. A thousand volts will sometimes appear in a line a thousand kilometers long if there are strong auroras overhead.
In the olden days of overland telegraph lines, the key operators sometimes were in for nasty surprises during auroral displays. Unwanted sparks erupted around their telegraph terminals, and the telegraph systems became unusable. Had the Alaska-Siberia Telegraph not been abandoned in 1867 before being completed, the system surely would have had much trouble with the aurora.
More important now is the current induced in long electrical transmission lines. The aurorally induced current is small compared to the 60 hertz current intentionally placed in a power transmission line, but even so, the auroral current surges have characteristics that do cause problems. The current finds it way into protective relays in the line and can cause them to trip off, stopping the power transmission. Power grids in eastern Canada and northeastern United States have undergone blackouts for this reason. Similarly, extensive auroral storms tripped off the power line between Winnipeg and Minneapolis during October 1980 and again in April 1981.
Still another problem with the auroral currents in power lines is that they create undesirable noise in the lines. The noise bothers people living near the power transmission lines and it may indicate undesirable mechanical and thermal stresses which reduce the useful lifetime of transformers; the damaging effects are thought to be cumulative.
Also, the induced currents can cause catastrophic failure of transformers during an auroral storm. An expensive 735 thousand volt transformer at St. James Bay, Canada, had to be replaced after the December 19, 1980 great red aurora, but it blew again during another display in April 1981.
The great red aurora seen by many Alaskans and Canadians on the early morning of December 19, 1980 fed current into the protective relays at the Gold Hill substation on the power line between Healy and Fairbanks, Alaska, but did not trip the relays. This line is comparatively short, so the induced current was not large.
Because of concern over problems they expect to occur as more long intertie power lines are built in the North, Drs. John Aspnes and Syun Akasofu and other scientists at the University of Alaska's School of Engineering and Geophysical Institute have begun investigating auroral induction in power lines in cooperation with the Golden Valley Electric Association in Fairbanks. Curiously enough, lack of funding now threatens to curtail this work, work which may save operators of power lines much money in the long run and which may help avoid power outages on such projects at the proposed intertie between Anchorage and Fairbanks.
