Generator Inter-turn Fault Protection Inter-turn fault have commonly been disregarded on the basis that if they occur they will quickly develop into earth faults. This is probably true if the fault is in the slot portion but will take a little longer in the region of the end connection. An approach of this kind is never attractive and may be entirely unjustified. There is a possibility of the machine being very seriously damaged before the fault evolves to a condition that can be detected by the longitudinal system. Modern medium size and large size turbo generators have the stator winding designed with only one turn per phase per slot. For these machines Inter-turn faults can only occur in case of double ground faults or as a result of severe mechanical damage of the stator end winding. The latter is considered rather unlikely to occur. It is generally considered difficult to obtain a reliable protection against short-circuiting of one turn if the stator winding has a la
Rotor Earth Fault Protection (64R1/64R2) The field circuit of generator (i.e. rotor winding) is an isolated D.C. circuit and not earthed anywhere. The field can be exposed to abnormal mechanical or thermal stresses due to vibration, excessive currents or choked cooling medium flow. This may result in a breakdown of the insulation between the field winding and the rotor iron at one point where the stress has been too high. A single earth fault in the field winding or its associated circuits, therefore, gives rise to a negligible fault current and does not represent any immediate danger. If however a second ground fault should occur, heavy fault current and severe mechanical unbalance may quickly arise and lead to serious damage. It is essential therefore that any occurrence of insulation failure is discover and that the machine is taken out of service as soon as possible. Normally the machine is tripped instantly on occurrence of second rotor earth fault. Three method are avai