Siemens 7SA511 Fault Loop Determination in Ungrounded Systems Optional, 3PH Faults = Control

7SA511 Line Protection Relay Reference A

Table A-7.Selected Measurement Quantities in Grounded Systems, with

Impedance Fault Detection

Fault Detection Phase Loops

L1-E

L2-E

L3-E

L1-L2

L2-L3

L3-L1

L1-E, L2-E

L2-E, L3-E

L1-E, L3-E

L1-E, L2-E

L2-E, L3-E

L1-E, L3-E

L1-E, L2-E

L2-E, L3-E

L1-E, L3-E

L1-L2, L2-L3

L2-L3, L3-L1

L3-L1, L1-L2

L1-E, L2-E, L3-E

L1-L2, L2-L3, L3-L1

L1-E, L2-E, L3-E

L1-L2, L2-L3, L3-L1

L1-E, L2-E, L3-E

L1-L2, L2-L3, L3-L1

Selected Loop

L1-E

L2-E

L3-E

L1-L2

L2-L3

L3-L1

L1-L2

L2-L3

L3-L1

L1-E

L2-E

L3-E

L2-E

L3-E

L1-E

L1-L2

L2-L3

L3-L1

L3-E

L3-L1

L3-L1

L3-L1

L3-E

L3-E

Selected Setting Parameter

irrelevant

irrelevant

2PH-E FLTS =

PHASE-PHASE

2PH-E FLTS =

LEADING PH-E

2PH-E FLTS =

LAGGING PH-E

irrelevant

3PH FAULTS =

E/F CONTROL

3PH FAULTS =

PH-PH ONLY

3PH FAULTS =

PH-E ONLY

A.3.3 Fault Loop Determination in Ungrounded Systems (Optional)

In isolated or compensated networks, currents resembling a short circuit are not present in the case of a single-phase ground fault. Only a displacement of the voltage triangle occurs, as illustrated in Figure A-7, and this condition does not represent any immediate danger to network operation. In this case, the distance protection must not trip since the phase-to-ground voltage of the faulty phase is zero throughout the network. A trip would lead to, at each measuring point, a measured impedance equal to zero for the faulty phase-to-ground loop. Therefore, pickup of one single phase-to-ground fault detector is avoided in the 7SA511 relay.

July 27, 1995 A-19