Inverse Time, Directional Time Overcurrent Elements 67-Toc, 67N-Toc - Siemens 7SC80 Manual

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Figure 2-26

Inverse Time, Directional Time Overcurrent Elements 67-TOC, 67N-TOC

2.3.4
The inverse time elements depend on the order variant. They operate either according to the IEC or the ANSI
standard or to a user-defined characteristic or a recloser characteristic. The characteristics and associated
formulas are identical to those of the non-directional overcurrent protection and are illustrated in the Tech-
nical Data. When the inverse time characteristics are configured, the definite time elements 67-2 and 67-1 are
additionally active.
Pickup Behavior
For each element, an individual pickup value 67-TOC PICKUP or 67N-TOC PICKUP is set which can be
measured as Fundamental or True RMS. Each phase and ground current is separately compared with the
common pickup value 67-TOC PICKUP or 67N-TOC PICKUP of each element. When a current value
exceeds the corresponding setting value by a factor of 1.1, the corresponding phase picks up and a message is
generated phase-selectively assuming that the fault direction is equal to the direction configured. If the inrush
restraint feature is used, either the normal pickup signals or the corresponding inrush signals are issued as
long as inrush current is detected. If the 67-TOC element picks up, the tripping time is calculated from the
actual fault current flowing, using an integrating method of measurement. The calculated tripping time
depends on the selected tripping curve. Once this time has elapsed, a trip signal is issued provided that no
inrush current is detected or inrush restraint is disabled. If the inrush restraint feature is enabled and an inrush
condition exists, no tripping takes place, but a message is recorded and displayed indicating when the overcur-
rent element time delay elapses.
For ground current element 67N-TOC PICKUP, the characteristic may be selected independently of the char-
acteristic used for phase currents.
Pickup values of the 67-TOC (phases) and 67N-TOC (ground current) and the associated time multipliers may
be set individually.
Each of these elements can work directionally or non-directionally.
Dropout Behavior
When using an ANSI or IEC characteristics, it can be selected whether the dropout of an element is to occur
instantaneously or whether dropout is to be performed by means of the disk emulation mechanism. "Instanta-
neously" means that pickup drops out when the pickup value of approx. 95 % of the set pickup value is under-
shot. For a new pickup, the time counter starts at zero.
The disk emulation evokes a dropout process (time counter is decrementing) which begins after de-energiza-
tion. This process corresponds to the reset of a Ferraris disk (explaining its denomination "disk emulation"). In
case several faults occur in succession the "history" is taken into consideration due to the inertia of the Ferraris
disk and the time response is adapted. Reset begins as soon as 90 % of the setting value is undershot, in
accordance to the dropout curve of the selected characteristic. In the range between the dropout value (95 %
of the pickup value) and 90 % of the setting value, the incrementing and the decrementing processes are in
idle state.
Disk emulation offers advantages when the overcurrent relay elements must be coordinated with conven-
tional electromechanical overcurrent relays located towards the source.
For recloser characteristics, an element drops out immediately after the value has fallen below a threshold.
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
Logic of the dropout delay for 67-1
2.3 Directional Overcurrent Protection 67, 67N
Functions
115