Siemens Siprotec 7UM611 Manual page 47

2.7 Definite-Time Overcurrent Protection (I>>, ANSI 50, 51, 67) with Direction Detection
Figure 2-6
The phase carrying the highest voltage is selected for the direction decision. With
equal current levels, the phase with the smaller number is chosen (I
I
short-circuit faults.
Table 2-2
If the phase-to-phase voltage used for the direction decision is below the minimum
value of approx. 7 V, the voltage is taken from a voltage memory. This voltage also
allows unambiguous direction determination if the short-circuit voltage has collapsed
(short circuit close to generator terminals). After the expiration of the storage time
period (2 cycles), the detected direction is saved, as long as no sufficient measuring
voltage is available. If a short circuit already exists at generator startup (or for motors
or transformers on connection), so that no voltage is present in the memory and no
direction can be determined, a trip is issued.
The direction detection can be disabled via binary input.
7UM61 Manual
C53000-G1176-C127-3
Cross-Polarized Voltages for Direction Determination
). The following table shows the allocation of measured values for various types of
L3
Allocation of Measured Values for the Determination Direction
Pickup
L1
L2
L3
L1, L2 with I >I
L1 L2
L1, L2 with I =I
L1 L2
L1, L2 with I <I
L1 L2
L2, L3 with I >I
L2 L3
L2, L3 with I =I
L2 L3
L2, L3 with I <I
L2 L3
L3, L1 with I >I
L3 L1
L3, L1 with I =I
L3 L1
L3, L1 with I <I
L3 L1
L1, L2, L3 with I >(I , I )
L1 L2 L3
L1, L2, L3 with I >(I , I )
L2 L1 L3
Selected Current
I
A
I
L2
I
L3
I
L1
I
L1
I
L2
I
L2
I
L2
I
L3
I
L3
I
L1
I
L1
I
L1
I
L2
before I before
L1 L2
Associated Voltage
U — U
L3 L3
U — U
L2 L3
U — U
L3 L3
U — U
L3 L3
U — U
L3 L3
U — U
L2 L3
U — U
L2 L3
U — U
L3 L1
U — U
L3 L3
U — U
L3 L3
U — U
L3 L3
U — U
L3 L3
U — U
L3 L3
U — U
L3 L1
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