Functions
2.11 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
192
Figure 2-70 Use of a user-defined Curve
Determination of Ground-faulted Phase
The phase connected to ground may be identified in an ungrounded
or resonant grounded system, if the device
is supplied by three voltage transformers connected in a grounded-wye configuration or the phase-Ground volt-
ages are calculated. The phase in which the voltage lies below setting VPH MIN (address 3106) is identified
as the faulty phase as long as the other two phase voltages simultaneously exceed setting VPH MAX (address
3107). The setting VPH MIN must be set to less than the minimum expected operational phase-to-Ground volt-
age. A typical setting for this address would be 40 V. Setting VPH MAX must be greater than the maximum ex-
pected operational phase-to-Ground voltage, but less than the minimum expected operational phase-to-phase
voltage. For V
Nom
= 100 V, approximately 75 V is a typical setting. These settings have no significance in a
grounded
system.
Displacement Voltage Element V
N
The displacement voltage 64-1 VGND (address 3109) or 64-1 VGND (address 3110) is the pickup of the
ground fault detection and a release condition for the direction determination (when setting the direction char-
acteristic to cos ϕ / sin ϕ). If the direction characteristic is set to V0/I0 ϕ mea., the displacement voltage
element is entirely independent of the current elements. Depending on the configuration at address 213 VT
Connect. 3ph, only the applicable limit value address 3109 64-1 VGND or 3110 64-1 VGND is accessible.
That is, if two phase-to-phase voltages and the displacement voltage V
0
are supplied to the device, the mea-
sured displacement voltage is used directly for ground fault recognition. The threshold for V
0
is set at address
3109 64-1 VGND, where a more sensitive setting can be made than with a calculated displacement voltage.
Please note that with displaced voltage V
0
-voltage, the factor (in normal case = 1.73; see also Section 2.1.3.2)
specified with parameter 206 Vph / Vdelta is used. For the display of the parameters 3109 64-1 VGND in
primary values, the following conversion formula applies:
If three phase-to-Ground voltages are connected to the device, the displacement voltage 3 · V
0
is calculated
from the momentary values of phase-to-Ground voltages, and address 3110 is where the threshold is to be
set. For the display of parameter 3110 in primary values, the following applies:
If the secondary values of (for example) parameters 3109 and 3110 are set equally, then their primary values
differ by adjustment value Vph / Vdelta.
To Next Page
Loading...
