Siemens SIPROTEC 7UM62 Manual page 70

Multifunctional machine protection

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2.9 Definite-Time Overcurrent Protection (I>>, ANSI 50, 51, 67) with Direction Detection

The phase carrying the highest current is selected for the direction decision. With equal current levels, the

phase with the smaller number is chosen (I

measured values for various types of short-circuit faults.

L1, L2 with I

L2, L3 with I

L3, L1 with I

L1, L2, L3 with I

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.

Cross-Polarized Voltages for Direction Determination

Allocation of Measured Values for the Determination Direction

). The following table shows the allocation of

Selected Current

C53000-G1176-C149-7, Release date 03.2010

Associated Voltage

SIPROTEC, 7UM62, Manual