Checks With Primary Values
287
7SS52 V4 Manual
C53000-G1176-C182-3
7.5 Checks With Primary Values
 The operational preparations according to Chapter 7.4, page 278 must be complet-
ed.
 Switch on the primary values.
7.5.1 Transformer Polarity
To check the polarity of a current transformer you will need an operating current of at
least 10% the rated current.
If the operation current is not sufficient, use test equipment for primary values.
Test steps
 Read out the isolator replica with DIGSI plant visualization. The output corresponds
to the plant status.
 Set all feeders with the parameter Bay status (XX12/CU),
(4500/BU), via the binary inputs of the bay units or easier locally at the operator pan-
el with the function key F1 out of service.
 If the protection works correctly, the differential current for the module ZPS-BSZ2
must be nearly zero. Additionally the module ZPS-BSZ1 (check zone) shows the
current differential, because putting the feeders out of operation does not influence
the module ZPS-BSZ1.
 In the bay units the differential and stabilizing currents of the check zone are dis-
played as well. Bus couplers display the currents of the adjacent bus zone on the
left. By this the transformer polarity can be checked locally at the bay units.
 Put one feeder into service (F1). Read out the differential and stabilizing currents
with DIGSI Plant Visualization or the measured value window with DIGSI. The result
corresponds to the product of feeder current and normalizing factor (CT transforma-
tion ratio). Otherwise you have to check whether the CT transformation ratio is cor-
rect. Set the feeder out of service.
 Repeat the previous step for each feeder.
 After that put all feeders out of service.
 Put the feeder with the highest current at the busbar into service and note down
the differential current of the module ZPS-BSZ2.
 Put the feeder with the next lower current at the busbar into service. If the polarity
is correct, the load direction corresponds to the load direction of the next higher cur-
rent. The differential current must increase. If the load direction is reversed, check
the configuration and the connections of the transformer.
 Repeat the previous step until all feeders at the busbar have been put into opera-
tion.
Warning!
Primary tests may only be carried out by qualified persons who are familiar with the
commissioning of protection systems, with the management of power systems and the
relevant safety rules and guidelines (switching, earthing etc.)
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