Application - ABB 615 series Technical Manual

Section 4
Protection functions
4.2.3.5
366
The Blocking mode setting has three blocking methods. In the "Freeze timers" mode, the
operation timer is frozen to the prevailing value. In the "Block all" mode, the whole
function is blocked and the timers are reset. In the "Block TRIP output" mode, the function
operates normally but the TRIP output is not activated.

Application

67NIEF is a ground-fault function dedicated to operate in intermittent and permanent
ground faults occurring in distribution and sub-transmission networks. Fault detection is
done from the residual current and residual voltage signals by monitoring the transients
with predefined criteria. As the function has a dedicated purpose for the fault types, fast
detection and clearance of the faults can be achieved.
Intermittent ground fault
Intermittent ground fault is a special type of fault that is encountered especially in
compensated networks with underground cables. A typical reason for this type of fault is
the deterioration of cable insulation either due to mechanical stress or due to insulation
material aging process where water or moisture gradually penetrates the cable insulation.
This eventually reduces the voltage withstand of the insulation, leading to a series of cable
insulation breakdowns. The fault is initiated as the phase-to-ground voltage exceeds the
reduced insulation level of the fault point and mostly extinguishes itself as the fault current
drops to zero for the first time, as shown in
that is, rapid changes in the form of spikes in residual current (IG) and in residual voltage
(VG), can be repeatedly measured. Typically, the fault resistance in case of an intermittent
ground fault is only a few ohms.
Figure 172. As a result, very short transients,
1MAC059074-MB A
615 series ANSI
Technical Manual