ABB RELION 620 Series Technical Manual page 439

1MAC504801-IB E
620 series ANSI
Technical Manual
The Slope section 2 setting is determined correspondingly:
Slope section 2 = Id2/Ib2 x 100 %
GUID-6E355F0D-D86F-4EC5-8B7B-78224862B137 V1 EN
The second turning point End section 2 can be set in the range of 100 percent to 500
percent.
The slope of operating characteristic curve of the differential function varies in three
different sections of the range.
Table 339: Different sections of the range and its operation
Sections Operation
Section 1 In section 1, where 0 percent Ir < Ib <
50 percent Ir, the differential current required for tripping is constant. The value of the
differential current is the same as the
trip value setting basically allows for the no-load current of the power transformer and
small inaccuracies of the current transformers, but it can also be used to influence the
overall level of the operation characteristic. At the rated current, the no-load losses of
the power transformer are about 0.2 percent. If the supply voltage of the power
transformer suddenly increases due to operational disturbances, the magnetizing
current of the transformer increases as well. In general, the magnetic flux density of the
transformer is rather high at the rated voltage and the rise in voltage by a few percent
causes the magnetizing current to increase by tens of percent. This should be
considered in
Section 2 Section 2, where
section 2 . In this section, the variations in the starting ratio affect the slope of the
characteristic, that is, how big a change in the differential current is required for tripping
in comparison with the change in the load current. The starting ratio should consider CT
errors and variations in the transformer tap changer position (if not compensated). Too
high a starting ratio should be avoided, because the sensitivity of the protection for
detecting inter-turn faults depends basically on the starting ratio.
Section 3 In section 3, where Ib >
slope is 100 percent, which means that the increase in the differential current is equal to
the corresponding increase in the biasing current.
End section 1 , with End section 1 being fixed to
Low trip value selected for the function. The Low
Low trip value .
End section 1 < Ib < End section 2 , is called the influence area of Slope
End section 2 , the slope of the characteristic is constant. The
Section 4
Protection functions
(Equation 47)
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