Fifty or 60? It just hertz

[shiawase raichou]

Quick question: Why is Japan's power grid split into two, with each half using a different AC frequency?

 

And does this pose any challenges to the rail network and the equipment used? For example, do locomotives need dual power systems?

 

Probably a search online would give me an answer to the first part, but I'm curious as to the challenges this presumably historical legacy poses to the rail network.

[bikkuri bahn]

In the 19th century, when Japan was upgrading its infrastructure, the region centered around Tokyo settled on a 50Hz system supplied by German firm AEG, while the Kansai region was supplied by GE, which used 60Hz.  As for the railway angle, maybe someone else can chime in.