Pole mounted transformers for station service in substations or to feed residential or commercial buildings are fitted with mounting lugs that are sized per the IEEE standard C57.12.20. The transformers covered by this standard are 500KVA and smaller; High voltage, 34,500V and below; Low voltage, 7970/13,800Y V and below.
In the realm of protective relaying, overcurrent protection is the simplest and an essential scheme. Phase and residual protection are quite common in the industry. Phase elements should be set carefully so as to afford protection for equipment downstream of it while not limit the load current in anyway. Residual currents can be set more sensitive than phase relays since they do not limit the load current. Between these two, it is easy to forget the negative sequence protection.