Siemens siprotec 7SA522 User Manual page 486

Installation and Commissioning
I Measured on a
4
Parallel Line
8-30
transformer in the phase from which the voltage in the voltage path is missing, is con-
nected. If the line carries load in the first quadrant, the protection is in principle sub-
jected to the same conditions that exist during an earth fault in the direction of the line.
At least one stage of the earth fault protection must be set to be directional (address
[[ of the earth fault protection). The pick-up threshold of this stage must be below
the load current flowing on the line; if necessary the pick-up threshold must be re-
duced. The parameters that have been changed must be noted.
After switching the line on and off again, the direction indication must be checked: in
the fault messages (refer also to Sub-section 7.1.1.3) the messages "() 3LFNXS" and
"() IRUZDUG" must at least be present. If the directional pick up is not present, either
the earth current connection or the displacement voltage connection is incorrect. If the
wrong direction is indicated, either the direction of load flow is from the line toward the
busbar or the earth current path has a swapped polarity. In the latter case, the con-
nection must be rectified after the line has been isolated and the current transformers
short-circuited.
Bus-
bar
Line
Figure 8-15 Polarity testing for I
Holmgreen-connection
In the event that the pick-up alarms were not even generated, the measured earth (re-
sidual) current may be too small.
Attention! If parameters were changed for this test, they must be returned to their
original state after completion of the test!
If I is the current measured on a parallel line, the above procedure is done with the
4
set of current transformers on the parallel line (Figure 8-16). The same method as
above is used here, except that a single phase current from the parallel feeder is
measured. The parallel line must carry load while the protected line should carry load.
The line remains switched on for the duration of the measurement.
If the polarity of the parallel line earth current measurement is correct, the impedance
measured in the tested loop (in the example of Figure 8-16 this is L1–E) should be re-
duced by the influence of the parallel line. The impedances can be observed as pri-
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qv†p‚rp‡Ãur…r
e
i’ƒh††Ã‚r
n
ƒuh†r
U U
e n
I
L1
I
L2
I
L3
I
4
, example with current transformers configured in a
4
L1
L2
L3
U U U U
L1 L2 L3 n
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7SA522 Manual
C53000-G1176-C119-2