Be mindful of impedance realities when running underground feeders:
IF the ground is saturated with conductors -- think salty soils, saturated ground with ionic soils -- then you're heating the soil.
This is the reason why ASEA ( Sweden ) became the world's expert in DC power transmission. Sweden has endless islands just off her coast -- which have to be powered from the national grid. Ages ago the experts ran in to your headache. The Poco was bleeding energy into heating up the Baltic Ocean. It's purely an AC/ Impedance effect.
By shifting over to DC, the inductance losses went to zero.
Electrical Contractor Magazine wrote up the San Francisco experience. Less than three years ago, a DC link was run under the bay direct to the city. It had to be DC because AC would've bled too much energy -- and also would've cooked the insulation.
It's probably out there on the Web.
Next, encapsulated transformers ALWAYS run hot to the human touch -- even when everything is perfect. The epoxy functions like a double fur coat. So, the only way that ANY heat can be shed is if the exterior is so hot you can't sit on it.
Their insulation is so robust, they can take such temperatures for forty-years.
In all of your post you provide no mention of your conductor sizes.
I'd skip any concern about reactive power issues. If you're not being billed for loading down the Poco, then it's nothing. 15kVA is a joke to the Poco.
You may want to re-calculate your taps. With the long run they should be different, not symetrical.
Lastly, Pocos get away with underground distribution because they wrap their grounded neutrals around their three hots. (Medium voltages, primary distribution, typical) (Each hot is given its own braided wrapper.)
This means that their inductance waves don't travel outside their cable bundles/ buried triplex schemes. This means radio and TV peace -- and supression of inductance waves into the soil.
When you ran your secondary conductors -- they weren't shielded. So your power is interacting with every inductable feature of nature -- such as soils that immitate sea water -- electrically.
If this is an issue, even larger conductors will not have a material impact. The impedance is coming from close association with the wrong kind of soil.
All of the above is opinion from a distance, so double check everything. Your soil conditions may actually be favorable and my supposition entirely misplaced.
Last edited by Tesla; 12/22/12 10:10 AM.
