VT Connect. 3ph = Vab, Vbc, VGnd means that two phase-to-phase voltages (open delta voltage) and
the displacement voltage V
GDN
are connected.
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 Types of the Voltage Transformers
Connection type Functions
Directional defi-
nite- time/inverse-
time overcurrent
protection phase
Directional defi-
nite- time/inverse-
time overcurrent
protection ground
Sensitive ground
fault detection
50Ns, 51Ns, 67Ns
Synchrocheck Fault locator
Van, Vbn, Vcn
yes yes yes
yes
3)
yes
Vab, Vbc,
VGnd
yes yes yes
yes
3)
yes
Vab, Vbc
yes
yes
1)
yes
2)
yes
3)
no
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 C Connection Examples.
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 Connection Principle for a Capacitive Voltage Measurement
Functions
2.1 General
50 SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
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