Loading at 150% of rated would not be unusual for a typical load profile. The rating is based on constant load and if the load is below rating for most of the day, the transformer can be overloaded for a couple hours with no loss of life.
Utilities may also find that allowing the load to reach a point where there is some loss of life can be more economical than replacement. The utility I used to work for had a loading policy of loading to 125% initially and replacement at 225%. This was based on a life cycle cost analysis that took loss of life into account, based on the standard referenced by busbar.
Normally, a transformer of this type can carry 300% of its normal rating for a short time without damage, and 150% of its rating for several hours without overheating.
The real deciding factor is where do you live, and what season is it? During the winter months transformers may be overloaded in the 200% range for several hours without any damage if you live in a "winter-wonder-land" such as I do.
Thanks for the opinions. Bottom line appears to be that although I can overload to 50% for short periods, I would not want to run the transformers continuously overloaded, particularly when the weather gets warm. Secondly, there is nothing special about pole-type transformers. They just folow the rules of normal liquid-filled transformers.
