ABB RELION 670 Series Technical Manual page 437

1MRK 502 066-UUS B
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
6
R
f
Compare &
Evaluate
SELECT REFERENCE
REG670
IEC10000325 V1 EN-US
Figure 232: Simplified logic diagram for 100% stator earth fault protection STTIPHIZ
1
2
3
4, 5
6
7
8
9
Technical manual
3
4
5
Z
Bare
Z
Measured
X
S
K2
ZRef1
7
ZRef2
ZRef3
ZRef4
ZRef5
tON=0.5s
95% Trip a
a>b
t
b
9
95% Stator earth fault protection
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).
The phasor of injected voltage U
from raw samples. Observe that phasors are calculated for the injected frequency.
The complex bare impedance is calculated from U
The complex measured impedance is derived as Z
The fault resistance (R
Fault
complex reference.
Selection of one (out of maximum 5) Z
Fourier filter to derive the phasor of zero sequence voltage at fundamental frequency
The 95% stator earth fault zero sequence over voltage function must operate in parallel with STTIPHIZ.
STTIPHIZ
2
1
I
u_i_sef
Inj
U u_u_sef
Inj
K1
U
N un
U
UN> = 5%
8
and phasor of injected current I
Inj
/ I
inj inj
Measured
) is calculated from the complex measured impedance and a selected
.
Ref
Impedance protection
GUID-77EA122E-56CE-48E7-952D-B120C8525256 v2
Uinj
Rshunt
I
U
REX060
IEC10000325-2-en.vsd
is calculated by using special filter
Inj
.
= Z * k1 + k2 .
bare
Section 7
431