New current transformer for bus differential protection

Perfect current transformers would make all differential relaying simple, but such transformers would be of excessive size and cost. A new idea in current transformer design makes it possible to maintain a linear relation between primary and secondary currents in a transformer of reasonable size, even where high current values, completely offset, are encountered. Such a current transformer is particularly valuable for applications where high speed bus differential protection is required. The basic principles of design and test results are reviewed showing that the air gap core current transformer retains a fixed ratio over the full range of current for which it is designed. There is thus made available a current transformer of reasonable size, which may be easily applied and may be used with simple relays.