Siemens 7SC80 Manual page 50

Functions
2.1 General
VT Connect. 3ph = Vab, Vbc, VGnd means that two phase-to-phase voltages (open delta voltage) and
the displacement voltage V
VT Connect. 3ph = Vab, Vbc means that two phase-to-phase voltages (open delta voltage) are
connected. The third voltage transformer of the device is not used.
The selection of the voltage transformer connection affects the operation of all device functions that require
voltage input.
The settings Vab, Vbc do not allow to determine the zero voltage. The protection functions working with the
zero voltage are inactive in this case.
Table 2-2
Connection type
Van, Vbn, Vcn
Vab, Vbc,
VGnd
Vab, Vbc
1) Direction determination is only possible by evaluating the negative sequence system (otherwise selection
of zero sequence system or negative sequence system)
2) With this type of voltage transformer connection, the current elements operate only in a non-directional
way, the voltage elements do not work.
3) The 4th voltage input Vx is used as reference voltage for the synchrocheck. If parameter 368 AssignMea-
sInput = INs,Ib,Ic,Vx=Ia, no synchrocheck is possible.
Measured values, which due to the chosen voltage connection cannot be calculated, will be displayed as dots.
The Appendix provides some connection examples for all connection types at
Capacitive Voltage Measurement
If you select the setting Cap. Volt.Meas. at address 369 VT Con Type, the voltage is measured via
socalled bushing capacitances. The inductive primary voltage transformers normally used are not used in this
case. Capacitive voltage measurement always measures the phase-to-ground voltages from the protection
device. The following figure shows this type of connection.
[7sc80-kapazitiver-u-anschluss-240113, 1, en_US]
Figure 2-5
50
are connected.
GDN
Connection Types of the Voltage Transformers
Directional defi- Directional defi-
nite- time/inverse- nite- time/inverse-
time overcurrent time overcurrent
protection phase protection ground
yes
yes
yes
Connection Principle for a Capacitive Voltage Measurement
Functions
Sensitive ground
fault detection
50Ns, 51Ns, 67Ns
yes yes
yes yes
yes 1) yes 2)
E50417-G1140-C486-A8, Edition 07.2017
Synchrocheck Fault locator
yes
yes 3)
yes
yes 3)
no
yes 3)
C Connection Examples.
SIPROTEC Compact, 7SC80, Manual