Settings - Siemens 7SC80 Manual

A setting equal to about half the ground current is to be selected. The measurement method should be SIN
φ, since capacitive ground current is most relevant here.
Resonant-Grounded System
In resonant-grounded systems, directional determination on the occurrence of a ground fault is more difficult
since the low residual wattmetric current for measurement is usually dwarfed by a reactive current (be it
capacitive or inductive) which is much higher. Therefore, depending on the system configuration and the posi-
tion of the arc-compensating coil, the total ground current supplied to the device may vary considerably in its
values with regard to magnitude and phase angle. The relay, however, must evaluate only the active compo-
nent of the ground fault current, that is, Ι
regard to phase angle measurement of all instrument transformers. Furthermore, the device must not be set
to operate too sensitive. When applying this function in resonant-grounded systems, a reliable direction deter-
mination can only be achieved when toroidal current transformers are connected. Here the following rule of
thumb applies: Set pickup values to about half of the expected measured current, thereby considering only the
residual wattmetric current. Residual wattmetric current predominantly derives from losses of the Petersen
coil. Here, the COS φ measurement method is used since the resistive residual wattmetric current is most rele-
vant.
Grounded System
In grounded systems, a value is set below the minimum anticipated ground fault current. It is important to
note that 3I0 DIR (current value RELEASE DIRECT.) only detects the current components that are perpendic-
ular to the directional limit lines defined at addresses 3124 and 3125. COS φ is the method of measurement
used, and the correction angle is set to –45°, since the ground fault current is typically resistive-inductive
(right section of Figure 2-81 "Directional curve for cos-ϕ-measurement" in the functional description of the
sensitive ground fault detection).
Electrical Machines
One may set the value COS φ for the measurement method and use a correction angle of +45° for electrical
motors supplied from a busbar in an ungrounded system, since the ground current is often composed of an
overlap of the capacitive ground current from the system and the resistive current of the load resistance (left
part of Figure "Directional characteristic for cos-ϕ-measurement" in the functional description of the sensitive
ground fault detection).
Information on the Configuration of the Current Threshold
With devices with sensitive ground fault input, generally settings may be entered in primary values with
consideration given to the ratio of the applicable current transformer. However, problems related to the reso-
lution of the pickup currents can occur when very small settings and small nominal primary currents are
involved. The user is therefore encouraged to enter settings for the sensitive ground fault detection in secon-
dary values.
2.13.5

Settings

Addresses which have an appended "A" can only be changed with DIGSI, under "Additional Settings".
The table indicates region-specific presettings. Column C (configuration) indicates the corresponding secon-
dary nominal current of the current transformer.
Addr. Parameter
3101 Sens. Gnd Fault
3102 CT Err. I1
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
cos ϕ. This demands extremely high accuracy, particularly with
Ns
C Setting Options
OFF
ON
ON with GF log
Alarm Only
1A 0.001 .. 1.600 A
5A 0.005 .. 8.000 A
2.13 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
Default Setting Comments
OFF (Sensitive) Ground Fault
0.050 A Current I1 for CT Angle
Error
0.250 A
Functions
265