ABB RED615 Technical Manual page 314

Section 4
Protection functions
308
Residual current Io and residual voltage Uo
COMP. COIL
R e R e
K K
FEEDER MEAS
FEEDER
INCOMER
I Iov
Ioj
ctot
Fault
U tres
Point
U tres
GUID-415078AD-21B3-4103-9622-712BB88F274A V2 EN
Figure 153: Typical intermittent earth-fault characteristics
Earth-fault transients
In general, earth faults generate transients in currents and voltages. There are
several factors that affect the magnitude and frequency of these transients, such as
the fault moment on the voltage wave, fault location, fault resistance and the
parameters of the feeders and the supplying transformers. In the fault initiation, the
voltage of the faulty phase decreases and the corresponding capacitance is
discharged to earth (→ discharge transients). At the same time, the voltages of the
healthy phases increase and the related capacitances are charged (→ charge transient).
If the fault is permanent (non-transient) in nature, only the initial fault transient in
current and voltage can be measured, whereas the intermittent fault creates
repetitive transients.
Iov
(Healthy
Feeder)
0.1
0
Uo
-0.1
-0.2
R
Ioj
f
-0.3
1YHT530004D05 D
Uo
Pulse width
400 - 800 s
Pulse interval
5 - 300 ms
(Faulty
Feeder)
Peak value
~0.1 ... 5 kA
Technical Manual
615 series