V
1
/ V
2
C
stat
R
N
+
Vinj
-
I
inj
R
d
a
b
ANSI11000011_2_en.vsd
Y
Y
ANSI11000011 V2 EN-US
Figure 228: Injection via open delta VT connection
It must be observed that the resistor
R
d
is normally applied for ferro-resonance damping. The
resistance
R
d
is will have very little contribution to the ground fault current as it has high
resistance. This injection principle can be used for applications with various generator system
grounding methods. It is therefore recommended to make the injection via the open delta VT on
the terminal side in most applications.
Accuracy for STTIPHIZ (64S) is installation dependent and it mainly depends on the characteristic
of grounding or voltage transformer used to inject signal into the stator. Note that large variation
of the ambient temperature and variation of stator capacitance and conductance to ground
between standstill and fully loaded machine will also limit the possible setting level for the alarm
stage. As a consequence 10 kΩ sensitivity can be typically reached without problem. Depending on
1MRK 502 066-UUS B Section 7
Impedance protection
425
Technical manual
To Next Page
Loading...
