Siemens 7SJ82 Manual page 570

Protection and Automation Functions
6.15 Sensitive Ground-Fault Detection
Depending on the setting of the Connection type parameter of the measuring point I-3ph as well as the
current terminal block used, the following different linearity and settings ranges result in addition to the
common application:
Connection Type of
the Measuring Point
I-3ph
3-phase
3-phase + IN
3-phase + IN-separate
With the use of the function within a 1-phase function group and therefore at a 1-phase measuring point
I-1ph, the following different linearity and settings ranges result:
Measuring Point
I-1ph
The method of measurement processes the sampled current values and filters out the fundamental compo-
nent numerically.
The methods of measurement are characterized by high accuracy and by insensitivity to harmonics, especially
the 3rd and 5th harmonics frequently present in the ground-fault (residual) current.
Ground-Fault Detection, Pickup
If the absolute value of the ground current 3I0 exceeds the threshold value 3I0> threshold value and
the absolute value of the zero-sequence voltage V0 exceeds the threshold value V0> threshold value,
the stage recognizes the ground fault. The direction determination (see the next paragraph) is started when
the V0 threshold value is exceeded. The direction result is indicated via the
General function block). If the direction result equals the parameterized direction (parameter Directional
mode), the stage picks up.
Direction Determination
Exceeding the threshold values by the zero-sequence voltage V0 is a criterion for the ground fault. The direc-
tion determination can be delayed from the occurrence of the zero-sequence voltage with the Dir. deter-
mination delay parameter to achieve steady-state measurands. The result form the direction determina-
tion is only valid if the absolute value of the ground current 3I0 has also exceeded its threshold value.
The following figure shows an example of the direction determination in the complex phasor diagram for the
cos-φ direction measurement method with a correction value of the direction straight lines from 0 (parameter
φ correction). The example is suitable for the determination of the ground-fault direction in an arc-
suppression-coil-ground system where the variable 3I0 ⋅ cos φ is decisive for the direction determination.
23 These values apply for a secondary rated current of 1 A. The values need to be multiplied by 5 when the secondary rated current is 5 A.
24 If the connection type is without IN, such as 3-phase, the current threshold value is a calculated 3I0 value.
25 If the connection type is with IN, such as 3-phase + IN, the current threshold value is a measured IN value.
26 These values apply for a secondary rated current of 1 A. The values need to be multiplied by 5 when the secondary rated current is 5 A.
570
Current Threshold 3I0/IN
Calculated 3I0 24
Measured IN 25
Measured IN and calculated
3I0 when IN > 1.6 A
Current Threshold
Measured
Current Terminal Block
4 x protection
3 x protection, 1 x sensitive 0.030 A to 35.000 A
4 x measurement
4 x Protection
4 x Measurement
3 x Protection, 1 x sensitive 0.001 A to 35.000 A
Current Terminal Block
Sensitive
Protection
Ground fault signal (in the
SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
3I0 Threshold Value
Settings Range
(Secondary) 23
0.030 A to 35.000 A
0.001 A to 1.600 A
0.030 A to 35.000 A
0.001 A to 1.600 A
3I0 Threshold Value
Settings Range
(Secondary) 26
0.001 A to 1.600 A
0.030 A to 35.000 A