Manual 7SJ45 Settings
C53000-K1174-C001-7 53
Determining the setting values
The high-current stage I>> is used for fast tripping that does not
depend on any selective tripping schedule; it is mainly used for
high-impedance equipment (transformers, paralleling reactors).
The high-current stage is set such that it only picks up in case of
a short-circuit upstream or inside of such equipment. It should be
kept in mind that transformers, reactors and motors may absorb
on power-up an increased magnetizing current (inrush current).
A short delay time may be required in the case of machines to
bridge the inrush current. Therefore a delay can be set for the I>>
stage.
The earth current stage IE> isausefulfunctioninnetworkswith
effective or resistance or reactance earthing. Set this stage to
somewhat less than thelowest earth faultcurrentto be expected.
For the time setting, a separate selective tripping schedule for
earth faults can be used.
The setting of the overcurrrent stage I> is mainly determined by
the maximum load current. It must be excluded that the device
picks up due to an overload while it is operated as a short-circuit
protection. In that case, the overcurrent stage should be set for
line protection to approx. 20 % above the highest (over-)load
current to be expected, and to approx. 50 % for transformer and
motor protection. When using the device downstream of
controlled or parallelly operated transformers, make sure that the
setting value is lower than the lowest short-circuit current to be
expected for the planned protection zone. Refer to the selective
tripping schedule for setting times.
Where the device is used for inverse-time overcurrent protection,
an interval of approx. 0.3 s (typical interval for selective tripping)
mustbe observedbetween the set characteristics of two adjacent
relays. These characteristics are set on the basis of the scale fac-
torTIporD(seeFigure2-11toFigure2-20).Sincedevice7SJ45
operates with disk emulation, please observe the reset character-
istics.
The definite time overcurrent protection of 7SJ45 operates with
disk emulation. It emulates the behavior of disks of electrome-
Table 2-2 Parameter allocation for DIP switches 2 to 5
SW 1 MODE I>>
High-current stage available
MODE I>>
High-current stage not
available
Evaluation of calculated IE
DT O/C 50/51 IEC 51 ANSI 51 DT O/C 50/51 IEC 51 ANSI 51
Black printing
applies!
White printing
applies!
Black printing
applies!
White printing
applies!
SW 2 I>> I>> I>> IE> IEp IEp
SW 3 TI>> TI>> TI>> TIE> TIEp DE
SW 4 I> Ip Ip I> Ip Ip
SW 5 TI> TIp D TI> TIp D
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