Transformer overcurrent protection

A method for determining when an electronic interrupting device will open in response to detecting overcurrent, the electronic interrupting device protecting a transformer having a winding in a power distribution network, the method comprising:

• obtaining a time/current through fault protection curve that is defined by a plurality of time/current points for the transformer that identifies when the transformer may experience thermal or mechanical damage in response to a certain current flow over a certain time in the transformer winding;
• selecting a time multiplier;
• determining an operating curve for the electronic interrupting device, wherein the operating curve identifies when the electronic interrupting device will open in response to a certain current flow over a certain time, by multiplying the multiplier and a time portion of each of the plurality of time/current points on the through fault protection curve for a first portion of the operating curve, and providing a two fundamental power frequency cycle portion of the operating curve that defines a current that if exceeded will cause the electronic interrupting device to operate after two fundamental power frequency cycles.

An electronic interrupting device associated with a transformer in power distribution network that is configured to interrupt current flow through the transformer in response to overcurrent to protect the transformer, the transformer having a time/current through fault protection curve that is defined by a plurality of time/current points for the transformer that identifies when the transformer may experience thermal or mechanical damage in response to a certain current flow over a certain time in the transformer winding the electronic interrupting device comprising:

• an operating curve for the electronic interrupting device in response to which the electronic interrupting device operates to interrupt current flow through the transformer, the operating curve having a multiplier portion defined by multiplying the multiplier and a time portion of each of the plurality of time/current points on the through fault protection curve, a two fundamental power frequency cycle portion defined by a current that if exceeded will cause the electronic interrupting device to interrupt current flow through the transformer after two fundamental power frequency cycles, and a one fundamental power frequency cycle portion defined by a current that if exceeded will cause the electronic interrupting device to open after one fundamental power frequency cycle.