Functions
2.3 Directional Overcurrent Protection Ground 67, 67N
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
96
Direction Determination via Ground Element using Negative Sequence Values
Figure 2-25 shows how the reference voltage for the directional ground element is processed using the nega-
tive sequence values based on a single-phase ground fault in phase A. The negative sequence voltage is used
as reference voltage; the negative sequence current is used as current for direction determination in which the
fault current is represented. The fault current -3I
2
is phase opposite to the fault current I
scA
and follows the
voltage 3V
2
by fault angle ϕ
sc
. The reference voltage is rotated by the setting value 1619 ROTATION ANGLE.
In this case, a rotation by -45°.
Figure 2-25 Rotation of the reference voltage, directional ground element with negative sequence values
The forward area is a range of ±86° around the rotated reference voltage V
ref,rot
If the vector of the negative
sequence current -3I
2
is in this area, the device detects forward direction.
2.3.9 Setting Notes
General
When selecting the directional ground overcurrent protection in DIGSI, a dialog box opens with several tabs for
setting the associated parameters. Depending on the functional scope specified during configuration of the pro-
tective functions in address 116 67N/67N-TOC, the number of tabs can vary.
When selecting 67N/67N-TOC = Definite Time, only the settings for the definite time elements are avail-
able. Selecting TOC IEC or TOC ANSI the inverse time characteristics will be available too. The superimposed
directional elements 67N-2 and 67N-1 apply in all these cases.
The directional ground current element can be turned ON or OFF at address 1601 FCT 67N/67N-TOC.
Depending on the parameter 613 Gnd O/Cprot. w., the device can operate using either measured values
IN or the quantities 3I0 calculated from the three phase currents. Devices featuring a sensitive ground current
input generally use the calculated quantity 3I0.
The directional orientation of the function is influenced by parameter 201 CT Starpoint (see Chapter 2.1.3).
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