ABB Relion 670 series, Technical Manual

Page: 437 / 1432

From the measured impedance the stator ground fault resistance can be estimated since the
reference impedance is known. An alarm level (Ω) is set at a higher value and the ALARM signal is
activated after a set alarm delay time. A trip level (Ω) is also set at a lower value. When the trip level
is reached a TRIP signal is activated as shown in figure 231 .
7.14.8.6 Simplified logic diagram
GUID-77EA122E-56CE-48E7-952D-B120C8525256 v2
Uinj
Rshunt
95% Stator earth fault protection
STTIPHIZ
REX060
REG670
1
I
U
u_i_sef
u_u_sef
X
S
a>b
a
b
K1
K2
U
UN> = 5%
t
tON=0.5s
95% Trip
un
Compare &
Evaluate
ZRef2
ZRef3
ZRef4
ZRef5
SELECT REFERENCE
3
8
2
4
5 6
7
9
IEC10000325-2-en.vsd
Measured
Z
Bare
Z
Inj
I
Inj
U
N
U
R
f
ZRef1
IEC10000325 V1 EN-US
Figure 232: Simplified logic diagram for 100% stator earth fault protection STTIPHIZ
1 The 100% stator earth fault protection function receives amplified injected voltage and current via the
REX060 unit as two voltage signals. (Voltage inputs in the REG670).
2 The phasor of injected voltage U
Inj
and phasor of injected current I
Inj
is calculated by using special filter
from raw samples. Observe that phasors are calculated for the injected frequency.
3 The complex bare impedance is calculated from U
inj
/ I
inj
.
4, 5 The complex measured impedance is derived as Z
Measured
= Z
bare
*
k1 + k2.
6 The fault resistance (R
Fault
) is calculated from the complex measured impedance and a selected
complex reference.
7 Selection of one (out of maximum 5) Z
Ref
.
8 Fourier filter to derive the phasor of zero sequence voltage at fundamental frequency
9 The 95% stator earth fault zero sequence over voltage function must operate in parallel with STTIPHIZ.
1MRK 502 066-UUS B Section 7
Impedance protection
431
Technical manual