Found this on a Japanese web site, all text was in Japanese, no English, so I don't know the details on this one

For those who can read Japanese, or use a translator program, this is the location:

http://www.tawatawa.com/densen1m/page011.html

これは今では見られない兜碍子です。

直流線に使われていたそうです。

これはかなり貴重です。

史料館に行ったら、この碍子はよく目に焼き付けた方が良いです。

This is the helmet insulator seen by now. It is used on DC lines. to This is quite valuable. It is better if you go to the archives this insulator is burned onto a good look.

For the rest of the story, start here:

http://www.microsofttranslator.com/bv.aspx?from=&to=en&a=http%3A%2F%2Fwww.tawatawa.com%2Fdensen1m%2Fpage002.html