Application - ABB RED615 Technical Manual

1YHT530004D05 D
4.2.3.5
615 series
Technical Manual
Blocking logic
There are three operation modes in the blocking functionality. The operation modes
are controlled by the BLOCK input and the global setting Configuration/System/
Blocking mode which selects the blocking mode. The BLOCK input can be
controlled by a binary input, a horizontal communication input or an internal signal
of the IED program. The influence of the BLOCK signal activation is preselected
with the global setting Blocking mode.
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 OPERATE output
mode, the function operates normally but the OPERATE output is not activated.

Application

INTRPTEF is an earth-fault function dedicated to operate in intermittent and
permanent earth 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 earth fault
Intermittent earth 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-earth 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 Figure 153. As a result, very short transients, that is, rapid changes in the
form of spikes in residual current (Io) and in residual voltage (Uo), can be
repeatedly measured. Typically, the fault resistance in case of an intermittent earth
fault is only a few ohms.
Section 4
Protection functions
307