Functions
2.3 Directional Gound Overcurrent Protection 67N
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
85
2.3.5 Interaction with Fuse Failure Monitor (FFM)
Spurious tripping can be caused by a measuring voltage failure due to a short circuit or phase failure in the
voltage transformer secondary system or pickup of the voltage transformer mcb (fuse). In the event of a single-
phase or two-phase failure of the measuring voltage, it is possible to recognize this condition and block the di-
rectional overcurrent time protection elements (ground), see logic diagrams. In such a case, the undervoltage
protection and the sensitive ground fault detection will also be blocked.
For additional information on the operation of the fuse failure monitor, see section 2.10.1 Measured Value Su-
pervision.
2.3.6 Dynamic Cold Load Pickup
It may be necessary to dynamically increase the pickup values of the directional time overcurrent protection if,
at starting, certain elements of the system show an increased power consumption after a long period of zero
voltage (e.g. air-conditioning systems, heating installations, motors). Thus, a general raise of pickup thresholds
can be avoided taking into consideration such starting conditions.
This dynamic cold load pickup function is common to all overcurrent elements and is described in Section 2.4.
The alternative pickup values can be set individually for each element of the directional and non-directional time
overcurrent protection.
2.3.7 Inrush Restraint
The 7SK80 features an integrated inrush restraint function. It prevents the "normal" pickup of the 67N-1 or 67N-
TOC elements (not 67N-2) in the ground path of the non-directional and directional overcurrent protection. The
same is true for the alternative pickup thresholds of the dynamic cold load pickup function. After detection of
inrush currents above a pickup value, special inrush signals are generated. These signals also initiate a fault
record and start the associated trip delay. If the inrush condition is still present after the trip delay has elapsed,
a corresponding message ("....TimeOut ") is output, but tripping is blocked (for further information see "Inrush
Restraint" in Section 2.2).
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