ABB RELION Series, Technical Manual

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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.
4.2.3.5 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 163 . 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.
Residual current Io and residual voltage Uo
FEEDER
FEEDER MEAS
Iov
Fault
Point
K
Re
-0.3
-0.2
-0.1
Residual
Current
(kA)
Residual
Voltage
x
10
2
(kV)
INCOMER
COMP. COIL
Ioj
Uo
K
Re
0
0.1
Ioj
(Faulty
Feeder)
Iov
(Healthy
Feeder)
Uo
Pulse width
400 - 800 s
Pulse interval
5 - 300 ms
Peak value
~0.1 ... 5 kA
Utres
Utres
I
ctot
Rf
GUID-415078AD-21B3-4103-9622-712BB88F274A V2 EN
Figure 163: Typical intermittent earth-fault characteristics
1MRS758755 A
Section 4
Protection functions
REC615 and RER615 321
Technical Manual