One of my projects at HYDAC is doing quite a bit of research into electrostatic discharge in Hydraulic Systems - which is a MASSIVE problem in the industry, but companies don't want to talk about it!!
Here is a video of some of the effects:
This causes a massive increase in the breakdown of oils, causing problems with pumps and varnish. Hydraulic systems to fatigue and fail.
You can read more about it in the description of the Youtube video.