Hi,
I know this is fairly late in the day, I live with a substation just over the fence at the back of my house, it's a big one that services approximately half of my estate. When I bought the house I researched living near one and like you could not find any decent answers.
I have lived here for the past 7 years and have never been so settled.
You probably have a distribution substation in the garden. The input for a distribution substation is typically at least two transmission or subtransmission lines. Input voltage may be, for example, 115 kV, or whatever is common in the area. The output is a number of feeders. Distribution voltages are typically medium voltage, between 2.4 and 33 kV depending on the size of the area served and the practices of the local utility.
The feeders run along streets overhead (or underground, in some cases) and power the distribution transformers at or near the customer premises.
In addition to transforming voltage, distribution substations also isolate faults in either the transmission or distribution systems. Distribution substations are typically the points of voltage regulation, although on long distribution circuits (of several miles/kilometers), voltage regulation equipment may also be installed along the line.
My research lead me to the following: check the cables going in and out of the substation, by me the feed in was the other side of the substation, the feed out runs up my drive. I felt comfortable buying my home with this information, I have also planted willow in front of it because I read that trees, fencing sheds etc break up EMF. Having said that the wall of your home will further break it up. It may all be for nothing but it made me feel a whole more comfortable living near it.
The thing even blew a gasket and exploded 6 months after we moved in, most of the area were without power for several hours while we were re-routed, after a few weeks a massive huge crane delivered a new transformer thingy to be installed and we were all switched back to it. my neighbours and I are comfortable living with it and do not feel any urge to get away.
Hope this helps. xx