The Mighty 477 Blog

In previous posts the mechanics by which Current Transformers convert high current flow in a conductor to a lower, easier to measure current was described. This is important when faults occur because of the resulting high current flow from a phase-to-phase or phase-to-ground fault. When a fault does occur, it is important not only to clear the fault as quickly as possible, but also to disconnect only what is needed and not shut the entire plant down if possible. This means that the equipment not only needs to sense a fault, but establish where the fault is occurring. If a fault occurs in Generator 4a, for instance, high current will flow from all the other generators on line as well as the rest of the grid. The motors that are circulating water and supplying fuel to the generators would also suffer from a generator fault, as the voltage drop will cause high current to flow in the motor windings. It would make little sense to trip all six generators, and all the transformers, and all the motors because one generator was shorted One of the schemes to locate a fault is Differential Fault Protection. Instead of using one Current Transformer to detect a fault, two are employed. In this diagram two C.T.s are used to protect a transformer. The C.T.s are connected in series, but the polarities are different.
Posted by Scott