Functions
2.8 Earth Fault Protection in Earthed Systems (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
218
The zero-sequence voltage is determined by its defining equation 3·U
0
=U
L1-E
+U
L2-E
+U
L3-E
. The zero-se-
quence voltage is measured or calculated depending on the application of the fourth voltage input U
4
of the
device. If the fourth voltage input is connected to the open delta winding U
delta
of a voltage transformer set and
if it is configured accordingly (address 210 U4 transformer = Udelta transf., see Section 2.1.2.1), this
voltage is used considering the factor Uph / Udelta (address 211, see Section 2.1.2.1). If not, the device
calculates the zero-sequence voltage from the phase voltages. Naturally, all three phase-to-earth voltages ob-
tained from a set of three star-connected voltage transformers must be available and connected to the device.
Definite time very high set current stage 3I
0
>>>
The triple zero-sequence current 3 I
0
is passed through a numerical filter and then compared with the set value
3I0>>>. If this value is exceeded an alarm is issued. After the corresponding delay time T 3I0>>> has ex-
pired, a trip command is issued which is also alarmed. The reset threshold is approximately 95 % of the pickup
threshold.
Figure 2-104 shows the logic diagram of the 3I
0
>>> stage. The function blocks „direction determination“, „per-
missive teleprotection“ and the generation of the signals „Line closure“ and „EF Inrush“ are common to all
stages and described below. They may, however, affect each stage individually. This is accomplished with the
following setting parameters:
• Op. mode 3I0>>>, determines the operating direction of the stage: Forward, Reverse, Non-
Directional or Inactive,
• 3I0>>> Telep/BI determines whether a non-delayed trip with the teleprotection scheme or via binary
input 1310 „>EF InstTRIP“ is possible (YES) or not (NO),
• 3I0>>>SOTF-Trip, determines whether during switching onto a fault tripping shall be instantaneous (YES)
or not (NO) with this stage.
• 3I0>>>InrushBlk which is used to switch the inrush stabilization (rush blocking) on (YES) or off (NO).
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