From Electricity Daily, January 20, 1998.

Commentary: Engineering Design and Montreal's Triangle of Darkness

As the Montreal electric power crisis unfolded last week, a serious issue
within the disaster has emerged, one with implications for the power industry as a whole. A week into the crisis a huge area south of Montreal, housing over one million people, was informed that it would see no restoration of power for another 1 to 2 weeks. This so-called "Triangle of Darkness" appears to be the victim of a series of unfortunate engineering judgments by Hydro Quebec, in its overall design for the main transmission grid.

First, HQ used very large capacity 735 kV transmission lines, in part because they must cover the vast distances to James Bay and Churchill Falls where the bulk of the utility's generation is located. Only three utilities in all of the U.S. and Canada use such big lines: HQ with over 6000 miles, American Electric Power with about 1800 miles of 765 kV lines, and New York Power Authority with 155 miles of 765 kV line connected to HQ.

Big lines concentrate risk, and most of Montreal's power comes from just six such lines. The crisis started when one of these went down early in the storm with the collapse of a series of 9 towers. In fact, during the storm a disproportionately high number of towers for the 735 kV lines failed -- over 150 compared to only a few dozen of the many 315 kV and 240 kV lines. This suggests that the big towers were under-designed for the ice loads they saw.

These massive transmission lines also formed the backbone for the local Montreal grid, which brought the risk in close. Failure of portions this backbone, actually a ring around the city, was the second blow. Service to the entire region is via feeder lines radiating outward from this ring,  ironically called the "ring of power", now better called the ring of pain. No other North American utility uses these large lines for an urban backbone. AEP's long lines are ties between its operating companies, and NYPA's is a tie to HQ that serves all of New York state.

Finally, the Montreal backbone ring had only a single line in its Southern portion. That made the risk absolute. The catastrophic failure of this line and its substations created the crisis in the Triangle of Darkness. The grid was crippled.

The extended blackout has clearly tarnished HQ's record inside the province and out. Tom Adams of the watchdog group Energy Probe in Ontario, a supporter of utility privatization, said the outages in Quebec "are the bitter fruits of an overly centralized system." Columnist Henry Aubin in the Montreal Gazette last week said that the government-owned utility, created by buying up privately-owned and municipal utilities in the 1960s, has enjoyed a long run as the "symbol of our engineering know-how and the flagship of Quebec's economy." But following the ice storm, he opined, "Hydro-Quebec will become an ex-icon, humbled, no longer entitled to a widespread assumption that it knows what is best for the people."

By coincidence the Federal Energy Regulatory Commission has scheduled a conference in February to discuss reliability issues. The Montreal ice storm should be a major topic of discussion. So too maybe Hydro Quebec's
grid design and the Triangle of Darkness.

--David Wojick

David E. Wojick, Ph.D., P.E.
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Copyright 1998 David E. Wojick. All Rights Reserved. Reprinted with permission.