99
Sudden current change function (SCC)
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The sudden current change function SCC measures the current increase per time unit
(di/dt) in all phases (one or two). In order to distinguish between heavy traction loads
and faults, it is used to enable the instantaneous trip from the measuring zone 2 and/or
the measuring zone 3 on the distance protection. The function can be activated or deac-
tivated via a binary input.
The sudden current change function’s operating modes may be selected from the fol-
lowing:
•
Off.
•
As start for zones 2 and 3 (Normal).
•
As start for zones 2 and 3 and as backup function when the primary protection is
down due to different reasons, e. g. blocking from the fuse failure supervision func-
tion (Backup).
The output signals from the sudden change current function should be configured to the
logical element for release of tripping from the impedance function, see figure in sec-
tion
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The current measuring element in one of the integrated signal processors continuously
measures the phase currents (IL1 and IL2) in two-phase systems and current IL1 in sin-
gle phase systems. The current signal is filtered by a low pass filter. The difference be-
tween the filtered value and the actual current value is calculated and compared with
the set operate value. The output signal SCC-START is activated instantaneously if the
measured current difference exceeds the set operate value. A timer delays the resetting
of the signal by the set time t.
The simplified logic diagram for the SCC function is shown in figure 45.
Summary of Contents for REO 517
Page 10: ... RQWHQWV ...
Page 16: ...6 Introduction to the application manual KDSWHU QWURGXFWLRQ ...
Page 64: ...54 Blocking of signals during test KDSWHU RPPRQ IXQFWLRQV ...
Page 88: ...78 Scheme communication logic ZCOM KDSWHU LQH LPSHGDQFH ...
Page 146: ...136 Unbalance protection for capacitor banks TOCC KDSWHU XUUHQW ...
Page 166: ...156 Dead line detection DLD KDSWHU 3RZHU V VWHP VXSHUYLVLRQ ...
Page 378: ...368 Monitoring of DC analog measurements KDSWHU 0RQLWRULQJ ...
Page 384: ...374 Pulse counter logic PC KDSWHU 0HWHULQJ ...
Page 412: ...402 Serial communication modules SCM KDSWHU DWD FRPPXQLFDWLRQ ...
Page 440: ...430 LED indication module KDSWHU DUGZDUH PRGXOHV ...