Heat waves, storms and blackouts
One of the world's worst blackouts has left more than 620 million people in India without power this week. Here at home, North Americans dealing with record high temperatures this summer have seen a jump in their energy costs as well as days-long power outages.
Writer Jenny Hall spoke with Professor Zeb Tate of the University of Toronto's Edward S. Rogers Sr. Department of Electrical and Computer Engineering about the relationship between heat, storms and the power grid.
Why do heat waves cause power outages?
Because air conditioners use a lot of power. In recent years, the peak loading of the system has been on the hottest days. Because of this, when grid operators doing load forecasting for the next day, temperature is the biggest contributing factor.
I read somewhere that Ontario had it sorted out its problems in terms of being able to cope with energy demand.
We have enough power capacity. But a lot of the infrastructure, particularly in the downtown area, is old and its not clear what state its in since much of it is underground.
Do we import power in Ontario? How does that work?
There are four grids in the U.S. and Canada. Theres one west of the Rockies known as the Western Interconnection. East of the Rockies, Ontario is on the same grid as everyone else. This is called the Eastern Interconnection. But Texas and Quebec each have their own grid.
In Ontario, we have the ability to import and export power to and from New York, Michigan, Minnesota, Manitoba and Quebec. If we have high demand in Ontario and our generation isnt sufficient or economical to run, we import power from elsewhere.
There were massive storms in the U.S. this summer that caused lengthy power outages. Why arent power lines all underground these days?
Its prohibitively expensive for transmission, which is the transfer of energy from power plants to substations closer to where demand is located. You dont see underground high voltage transmission. You do see it in distribution systems, which transfer energy from substations to neighbourhoods.
So when they have these big storms it doesnt necessarily matter whether the distribution lines are buried, its the transmission lines that are the problem.
I guess we only notice the power system when it doesnt work.
Thats right. The reliability of the power grid is pretty goodto the point where we usually just take it for granted.
What do you do?
Im trying to help the operators better understand whats happening in the grid right now so they can anticipate problems. For example, if a cloud is passing over a solar farm or the wind isnt blowing, operators need to know this so they can keep the supply and demand balanced. Looking forward, we want to be able to identify events that could cause problems on the grid and position it so that if any one thingor even two thingswere to fail, the system can handle it.
Doing this can be very hard computationally. For example, lets say we have 1,000 lines in the system. Then we have to run 1,000 simulations every time the system changes if we want to make sure none of those 1,000 potential outages causes a problem. This becomes a computational problem and its even more challenging if more complex events are considered.
When there are outages, why are some people blacked out and not others?
The power system is run so that well disconnect customers if in doing so we can save a piece of equipment and can quickly bring the customers back on line. Its a lot harder and more expensive to replace equipment than it is to let someone go offline for five minutes. Most of this is done automatically by devices in the system. For example, if a line hits a tree, the protection system will see the increase in current and trip the line off. This will disconnect anyone who is downstream.
So when the power goes off, sometimes its purposefully being turned off.
Thats almost always whats happening. They want to reduce customer outages, but on the other hand they dont want to have a sustained overcurrent either, because this will cause more permanent damagethings will catch fire.
My last question is about the big blackout in August of 2003. What happened there?
Essentially, one of the power companies hadnt been properly trimming their trees in Ohio. They had some outages in their system that they didnt know about and were operating within normal limits, so they didnt shift the generation or disconnect any customers. If theyd turned off Cleveland, for example, the blackout might not have happened.
There were a few other causes, too. The computer system of the operator monitoring the grid in that area wasnt working that day. All of these causes came together. If any one of them hadnt happened, chances are we would have been fine.
So it was a perfect storm of sorts.
Yes. This is why blackouts like that are rare. The system is operated so that if any one thing goes out, it doesnt break the system.