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3-24
Protection Functions
857-UM001A-EN-P – July 2009
Polarization
The negative zero sequence voltage –U
the angle reference for I
energizing input U
or it is calculated from the phase voltages
0
internally depending on the selected voltage measurement mode (see
"Voltage Measurement Mode" in Chapter 5):
•
LN: the zero sequence voltage is calculated from the phase
voltages and therefore any separate zero sequence voltage
transformers are not needed. The setting values are relative to the
configured voltage transformer (VT) voltage/√3.
•
LL+U
: The zero sequence voltage is measured with voltage
0
transformer(s) for example using a broken delta connection. The
setting values are relative to the VT
in configuration.
NOTE: The U
signal must be connected according the connection
0
diagram (Figure 9.14 in Chapter 9) in order to get a correct polarization.
Please note that actually the negative U
device.
Modes for different network types
The available modes are:
•
ResCap
This mode consists of two sub modes, Res and Cap. A digital
signal can be used to dynamically switch between these two sub
modes. This feature can be used with compensated networks,
when the Petersen coil is temporarily switched off.
-
Res
The stage is sensitive to the resistive component of the
selected I
signal. This mode is used with compensated
0
networks (resonant grounding) and networks earthed with
a high resistance. Compensation is usually done with a
Petersen coil between the neutral point of the main
transformer and earth. In this context "high resistance"
means, that the fault current is limited to be less than the
rated phase current. The trip area is a half plane as drawn in
Figure 3.16. The base angle is usually set to zero degrees.
-
Cap
The stage is sensitive to the capacitive component of the
selected I
signal. This mode is used with unearthed
0
networks. The trip area is a half plane as drawn in Figure
3.16. The base angle is usually set to zero degrees.
is used for polarization i.e.
0
. This –U
voltage is measured via
0
0
secondary voltage defined
0
, –U
, is connected to the
0
0
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