REG 316*4 1MRB520049-Uen / Rev. F ABB Switzerland Ltd
3-111
3.5.10. Inverse time NPS (NPS-Inv)
A. Application
Negative phase sequence protection especially of large genera-
tors subject to high thermal utilisation against excessive heating
of the rotor due to an asymmetric load.
B. Features
· inverse time delay according to level of NPS
(see Fig. 3.5.10.1)
· wide setting ranges for the parameters determining the oper-
ating characteristic
· adjustable rate of counting backwards when the overload
disappears (cooling rate of thermal image)
· insensitive to DC components
· insensitive to harmonics
· three-phase measurement.
C. Inputs and outputs
I. Analogue inputs:
· current
II. Binary inputs:
· blocking
III. Binary outputs:
· pick-up
· tripping
IV. Measurements:
· proportion of negative-sequence current component
I
2
=
1
/
3
(I
R
+ a
2
I
S
+ a I
T
).
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