book review

Electric power systems: a conceptual introduction
by A. von Meier
Reviewed by T.J. Nelson

he electrical grid isn't just a generator supplying a bunch of customers any more. It's actually very sophisticated. It has to be.

In the old days, generators and consumer devices were designed to handle 10 or 20% excess load. But economic pressures, says von Meier, forced engineers to eliminate those safety margins. The same is true of power systems.

Unlike the Internet, where each packet follows a unique optimized route, the electric grid has loops and redundant pathways. This means power flows toward power stations as well as away from them. Controlling a network like this is very complicated: if a power station on one side of the country increases its output to meet an increase in demand, it can overload a transmission line thousands of miles away and cause millions of dollars of damage. Generators must not only synchronize their waveforms and meet the load, they also must balance reactive power that comes from impedances in the lines and in the load, 40% of which consists of electric motors.

Big electric generators wouldn't even be possible without the use of hydrogen gas to keep them cool; ordinary air is just too viscous. Indeed, though the electrical grid is designed to stabilize itself automatically, margins are so tight these days that without computers the entire grid would be unstable. Those big displays in power stations might look old-fashioned, but there's some complicated math behind them.

Some systems are better than others: the electric grid in communist East Germany was built to such low standards that it was impossible to tie it to the Western grid; East German electricity had to be converted to DC and then back to AC to integrate it with western grid.

The same problem occurs with wind turbines, which, von Meier explains, must use induction generators for technical reasons. Induction generators cannot control bus voltage or reactive power output, and even have trouble controlling AC frequency. This is tolerable on the grid only as long as their system penetration is low; they cannot be considered a resource on par with synchronous machines unless their current is rectified and then inverted back to AC, which is inefficient.

That's why wind turbines and distributed generation systems are mostly considered a nuisance by power station operators. Not only is their power quality poor, they are not dispatchable, which means they're hard to activate remotely when they're off and they're a hazard to repairmen when they're on.

The math, mostly big Jacobian matrices of partial differential equations, is well described in other more advanced textbooks. There are many other books that discuss simple electric stuff. But to understand it intuitively there's a need for a conceptual overview of what is actually going on in a grid. That is the goal of this book.

This book assumes no background in physics, math, or electricity. The first 200 pages are a very simple, easy to understand background in electronics: what is a power angle, how power stations match frequencies, how impedances affect phase, why AC power lines can't be used underwater, and so forth. Then in chapter 7 the author puts it all together in an example of a power flow analysis. She makes it sound easy, but even with only six nodes, the power flow diagram can only be solved numerically.

You won't learn how to calculate much in this book, but you'll come away with an appreciation of how sophisticated the electrical grid really is. So when you drive around taking pictures of 500,000-volt pylons to impress your friends, you can give them something more to think about than just the cool telephone poles.