Siemens SIPROTEC 7SJ62 Manual page 236

Functions
2.12 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
That is, if two phase-to-phase voltages and the displacement voltage V
sured displacement voltage is used directly for ground fault recognition. The threshold for V
3108 (7SJ62/63) or 3109 (7SJ64), where a more sensitive setting can be made than with a calculated dis-
placement voltage. The upper setting threshold for 7SJ64 is higher than for 7SJ62 (see Technical Data). Please
note that with displaced voltageV
parameter 206 Vph / Vdelta is used. For display of parameters 3108 64-1 VGND or 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
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 3108 and 3110 are set equally, then their primary values
differ by adjustment value Vph / Vdelta.
Example:
Parameter 202
Parameter 203
Parameter 206
Parameter 213
Parameter 3108
The following applies when switching to primary values:
With the following configuration
Parameter 213
Parameter 3110
the following applies when switching to primary values:
With regard to a ground fault in a ungrounded or resonant-grounded system, nearly the entire displacement
voltage appears at the device terminals, therefore the pickup setting is not critical, and typically lies between
30 V and 60 V (for 64-1 VGND with a standard V0-connection) or 50 V and 100 V (for 64-1 VGND). Large fault
resistances may require higher sensitivity (i.e. a lower pickup setting).
With regard to a grounded system, a more sensitive (lower) pickup value may be set, but it must be above the
maximum anticipated displacement voltage during normal (unbalanced) system operation.
Pickup of just the voltage element may initiate time delayed tripping assumed that ground fault detection is con-
figured to perform tripping (address 3101 Sens. Gnd Fault = ON or ON with GF log) and moreover
address 3130 PU CRITERIA is configured Vgnd OR
64-1 DELAY. It is important to note that the total tripping time consists of the displacement voltage measure-
ment time (about 50 ms) plus the pickup time delay (address 3111 T-DELAY Pickup) plus the tripping time
delay (address 3112 64-1 DELAY).
236
, the factor (in normal case = 1.73; see also Section 2.1.3.2) specified with
0
Vnom PRIMARY
Vnom SECONDARY
Vph / Vdelta
VT Connect. 3ph
64-1 VGND
VT Connect. 3ph
64-1 VGND
are supplied to the device, the mea-
0
= 12 kV
= 100 V
= 1,73
= Vab, Vbc, VGnd
= 40 V
= Van, Vbn, Vcn
= 40 V
INs. The tripping delay is then set at address 3112
C53000-G1140-C207-2, Release date 01.2008
is set at address
0
is calculated
0
SIPROTEC, 7SJ62/64, Manual