Inverse Time, Directional Time Overcurrent Elements 67-Toc, 67N-Toc - Siemens SIPROTEC 4 User Manual

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Figure 2-26

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

2.3.4
Inverse time elements are dependent on the variant ordered. They operate either according to the IEC- or the
ANSI-standard or to a user-defined characteristic. The characteristics and associated formulas are identical
with those of the non-directional overcurrent protection and are given in the Technical Data. When the inverse
time curves are configured, the definite time relay elements (67-2, 67-1) are also available.
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 be directional or non-directional (non-directional from V4.81 on).
Dropout Behavior
When using an ANSI or IEC curve, it can be selected whether the dropout of an element is to occur instantane-
ously or whether dropout is to be performed by means of the disk emulation mechanism. "Instantaneously"
means that pickup drops out when the pickup value of approx. 95 % of the set pickup value is undershot. 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.
User-defined Characteristics
When user-defined characteristic are utilized, the tripping curve may be defined point by point. Up to 20 value
pairs (current, time) may be entered. The device then approximates the characteristic, using linear interpola-
tion.
SIPROTEC 4, 7SJ62/64, Manual
C53000-G1140-C207-8, Edition 08.2016
Logic of the dropout delay for 67-1
2.3 Directional Overcurrent Protection 67, 67N
Functions
91