Siemens 7SC80 Manual page 54

Functions
2.1 General
LoPo/LPS Current Connection (Low Power Sensor/Line Post Sensor)
Alternatively to the conventional current inputs, you can also use LoPo/LPS inputs. LoPo/LPS current inputs are
available as ordering options. In contrast to the standard current inputs, they calculate the ground current
instead of measuring it. Measurement methods working with ground current are therefore less accurate for
LoPo/LPS current connections.
Current sum monitoring is not possible. Parameter 368 AssignMeasInput allows using the ground fault
detection function.
At address 330 Iph-prim nom, you can set the primary rated phase current for the protection functions. The
parameter corresponds to address 204 CT PRIMARY for a standard current connection.
Parameters Iph-LPS prim and Vph-LPS I sec represent the transformation ratio for the LoPo/LPS.
At address 331 Iph-LPS prim you can specify the primary rated current of the current LoPo/LPS for the 3
phase currents.
At address 332 Vph-LPS I sec you can specify the secondary voltage of the current LoPo/LPS.
Common values of the current/voltage ratio are, for example, 300 A/225 mV (in acc. with the IEC 60044-8
standard) or 600 A/10 V.
The measuring range of the current sensor inputs ranges from 10 mV to 50 V, higher values are not measured.
Dependent on the transformation ratio of the current sensor, most diverse measuring ranges can thus be real-
ized. The inputs' impedance is 40 kΩ.
When using a 300 A/225 mV current sensor, currents from approx. 5 A can thus be measured; with different
transformation ratios, correspondingly lower currents.
The allowed range of secondary nominal phase current for protection in 7SC80 firmware is from 15 mV to 25
V. If it is out of range, indication 2184
blocked to avoid unexpected operation. The secondary nominal phase current for protection is calculated as
follows:
[fo_lopo_lps_current_connection, 1, en_US]
LoPo/LPS Voltage Connection (Low Power Sensor/Line Post Sensor)
Alternatively to the conventional voltage inputs, you can also use LoPo/LPS inputs. LoPo/LPS voltage inputs are
available via parameters.
If you are using LoPo/LPS voltage transformers, select in the function scope at address 369 VT Con Type the
setting Low Power / Line Post Sensor. With parameter 326 Vnom LPS prim you specify the primary rated
voltage (phase-to-phase quantity) of the voltage transformers. The setting value for parameter 327 Vnom LPS
sec is obtained from the primary rated voltage and the transmission ratio of the voltage transformers.
If set correctly, the inputs of the 7SC80 measure the value of parameter Vnom LPS sec when rated voltage
is present at the protected object. Common values of the voltage ratio are, for example, 20 kV/√3 / 3,25 V/√3
(in acc. with the IEC 60044-7 standard) or 6154:1.
In this example, parameter 326 Vnom LPS prim has to be set to 20 kV and 327 Vnom LPS sec to 3.25 V. In
this case, 3.25 V/√3 = 1.88 V are present at the measuring input in the case of rated voltage. However, 100 V
secondary are displayed in the protection device for the phase-to-phase voltages. With this device-internal
standardization to 100 V, the secondary value range is adapted to the operating range of the protection func-
tion as it is designed for conventional voltage transformers. As a consequence, not the ratio 326 Vnom LPS
prim and 327 Vnom LPS sec but the ratio 326 Vnom LPS prim and 100 V is used for the primary/secondary
conversion of the parameter setting values.
The measuring range of the voltage sensor inputs VA, VB, VC, and Vx ranges from 100 mV to 250 V.
Dependent on the transformation ratio of the voltage sensor, most diverse measuring ranges can thus be real-
ized.
The voltage inputs' impedance is 1.2 MΩ. If voltage sensors are designed for different impedances, for
example, for 200 kΩ, these can be adapted using the amplitude correction factor parameters 346 VT A AMPL
COR to 349 Vx AMPL COR.
54
CT LPS mismatch occurs and the function of the device will be
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017