Protective Elements
The following signals cannot become true if Id<Idmin:
87. Slope Blo
87. H2,H4,H5 Blo
87. Blo H2
87. Blo H4
87. Blo H5
87. Restraining
The signal restraining will become true if “87. Slope Blo” or
“87. H2,H4,H5 Blo” is true.
Example on Setting the Differential Function for Transformer Application
Setting the differential module will be described here with focus on the differential functionality. The protective
device asks for nearly all type-plate data of the transformer to allow for optimal adjustment of the differential
function without the need of an auxiliary transformer and other tools like CT tapping (especially that known from
non-digital relays in the past).
This results in the fact that the relay takes automatically these numeric values into account:
• CT ratio and its deviation from full load amperage at each winding of the transformer;
• Transformer ratio with respect to amplitude and transformer vector-group; and
• Ratio change by tap changer displacement.
All this is compensated internally for by numeric means.
SN:
Nominal, rated capacity of the transformer - basis for calculating the full load amperage of the transformer.
Example
78 MVA
Pri V:
Rated voltage of the transformer regarding winding 1.
Example
118 kV
Sec V:
Rated voltage of the transformer regarding winding 2.
Example
14.4 kV
By means of these three settings, the following full load amperage Ib is calculated, which is defined as the full load
amperage for the maximum allowed apparent power of the transformer. There is one full load amperage for each
winding, but differential protection results are always displayed in relation to Ib of the winding 1.
Example:
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