Functions
2.11 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
184
2.11.2 Ground Fault Detection for V0/I0-ϕ Measurement
Voltage Element
The voltage element relies on a pickup initiated by the displacement voltage V
0
or 3 · V
0
. Additionally, the faulty
phase is determined. The displacement voltage V
0
can be directly applied to the device, or the summation
voltage 3 · V
0
can be calculated according to the connection type of the voltage transformer (see also Param-
eter 213 VT Connect. 3ph in Section 2.1.3). When setting Van, Vbn, Vcn, the calculation of the summa-
tion voltage 3 · V
0
is based on the three phase-to–Ground voltages. The three voltage inputs must therefore be
connected to the voltage transformers in a grounded-wye configuration. When setting Vab, Vbc, VGnd, the
three phase-to-Ground voltages of both connected phase-to-phase voltages and the connected displacement
voltage are calculated. If the device is only provided with phase-to-phase voltages, it is not possible to calculate
a displacement voltage from them. In this case, the direction cannot be determined.
If the displacement voltage is calculated, then:
3 · V
0
= V
A
+ V
B
+ V
C
If the displacement voltage is directly applied to the device, then V
0
is the voltage at the device terminals. It is
not affected by parameter Vph / Vdelta (address 206).
The voltage element is not available with capacitive voltage measurement.
Pickup performed by the displacement voltage can be delayed (64-1 DELAY) for tripping.
After the voltage element picks up due to detection of a displacement voltage, the grounded phase is identified,
if possible. For this purpose, the individual phase-to-Ground voltages are measured or calculated, irrespective
of the connection type of the voltage transformers. If the voltage magnitude for any given phase falls below the
set threshold VPH MIN, that phase is detected as the grounded phase as long as the remaining phase-to-
Ground voltages exceed the set threshold VPH MAX.
Figure 2-63 Determination of Ground-faulted Phase
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