Siemens SIPROTEC 7UM62, Manual

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3 Installation and Commissioning
356
7UM62 Manual
C53000-G1176-C149-3
To eliminate interference which might originate from the running machine, in particular
from the excitation system, it is recommended to perform an additional operational
check as described in Section 3.4.9.2.
3.3.8 Checking the 100–% Stator Earth Fault Protection
The 100-% stator earth fault protection can be checked with the machine at stand-still,
because the measuring principle for the earth resistance calculation is independent of
whether the machine is at stand-still, rotating or excited. As a prerequisite for the
check, however, a supply for the 20 Hz generator 7XT33 must be provided; depending
on the project in hand, this may be a DC voltage supply or an external voltage source
(3 x 100 V, 50/60 Hz) (see also the connection diagram of Figure A-37 in the Appen-
dix).
Switch the 100-% stator earth fault protection to Block relay (address
5301 100%
SEF-PROT.
).
For the following parameters, the default settings must be maintained for a first com-
missioning.
5309 PHI I SEF
= 0°
5310A SEF Rps
= 0.0
Ω
5311A Rl-PARALLEL
=
∞
Ω
The measured quantities U
SEF
and I
SEF
fed to the device can now be read out in the
earth fault measured values (in DIGSI under Ins (earth fault measured values)):
U SEF=
xx.x V
I SEF=
xx.x mA
Please note that these measurements are pure r.m.s. values which only correspond
to the 20 Hz quantities if the generator is standing still. The voltage measured is influ-
enced by the loading resistor R
L
, the 20 Hz resistance of the band pass (R
BP
approx.
8
Ω
), the voltage divider (ü
Vlt.Divider
, usually 5/2) and, in the final analysis, by the 20 Hz
supply voltage (U
20Hz generator
, approx. 25 V). The value can be estimated as follows:
The flowing current I
SEF
is determined by the stator earth capacitance and is very
small.
The device calculates from these values the earth resistance
R
SEF
referred to the pro-
tection device side. The primary earth resistance
R
SEFp
on the machine side is ob-
tained by multiplying the secondary value with the conversion factor set in the Power
System Data 1 (address
275 FACTOR R SEF
). Both resistance values, including the
phase angle between the 20 Hz voltage and the 20 Hz current (
ϕ
SES
=
ϕ
U
-
ϕ
I
) can be
read out in the operational measured values:
R SEF=
= xxxx
Ω
RSEFp=
xxx.xx k
Ω
j
SEF= xx.x°
In fault-free condition, the measured phase angle
ϕ
SES
across the existing stator
earth capacitances should be approx. –90°. If it is not, the value to complement it to –
U SEF
R
L
R
BP
R
L
+
------------------------
U
20Hz-generator
ü
Vlt.Divider
---------------------------------------
⋅
=