5.2.3.2 FunctionalityThe transient/intermittent earth-fault protection (INTRPTEF) is a sample basedfunction designed for the protection and clearance of intermittent and transient earthfaults in distribution and sub-transmission networks. Fault detection is done from theresidual current and residual voltage signals by monitoring the transients withpredefined criteria.The operate time characteristics are according to definite time (DT).The function contains a blocking functionality. Blocking deactivates all outputs andresets timers.5.2.3.3 ApplicationINTRPTEF is a dedicated earth-fault function to operate in intermittent and transientearth faults occurring in distribution and sub-transmission networks. The functionhas selectable modes for corresponding fault types. As the function has a dedicatedpurpose for these fault types, fast detection and clearance of the faults can be achieved.Intermittent earth fault in compensated networksAn intermittent earth fault is a special type of fault that is encountered especially incompensated networks with underground cables. With underground distributioncables, the wire insulators may get damaged due to short transients in I0 and rapidchanges in U0 caused by water creating a connection between the connector and theground. This can be characterized as a series of cable insulation breakdowns becauseof the reduced voltage withstand.A070759 V1 ENFigure 76: Typical intermittent earth-fault residual current and residual voltagesignals on a faulty feederIntermittent earth-fault transients cause damping sinusoidal residual voltage. In caseof successive intermittent transients, the residual voltage level may continuously stayhigh. The substation residual voltage has usually been used in the substation back-up1MRS756378 D Section 5Protection functionsREF615 155Application Manual
