AC Power Frequency in Japan

Reading all of the awful news about the tragedy in Japan, I learned an engineering fact which surprised me.

As you may know, the AC power systems in different countries operate at different frequencies, in addition to operating at different voltages. I already knew that because when I used to do hardware, we needed to worry about this if we wanted to sell in multiple countries. I’d always learned that the general rule was that US systems operate at 60 Hz while the rest of the world operates at 50 Hz. Of course, it’s never that simple. There are plenty of exceptions to this rule. You can find some of them at this Wikipedia page.

But the most surprising exception is that Japan uses two different frequencies. The north of the country is 50 Hz while the south of the country is 60 Hz. Here’s a map from Wikipedia.

That’s the big reason that they’re having so much trouble with blackouts in Tokyo. It’s difficult to tie together two grids which are operating at different frequencies. There are only three frequency convertors connecting the two grids, and they have very limited capacity. This means that they can’t really shift a lot of power between them to load balance for all of the reactors which have been shut down in the north.

Here’s an article from IT World which explains this, and gives the historical background. It dates back to the 1890’s.

My company has an office in Tokyo. Everyone there is fine, but they’ve had a pretty rough week. They all slept in the office the first night because the trains weren’t running. The commute is still pretty awful and they’ve had repeated rolling blackouts.

Tom is planning to visit southern Japan this summer. Obviously things are pretty up in the air at the moment. We hope to know in a week or two exactly what’s going on.