Siemens 7SA511 manual Fault Detection Module Measured Ground Fault Current Voltage

7SA511 Line Protection Relay Method of Operation

In grounded systems, the measured line loop depends on the ground fault detection function (section A.2.1) and the parameter, 1PH FAULTS (address 1705), selected according to Table A-

2.In ungrounded system, the phase-to-phase loop is always selected in the case of a single-phase pickup without ground fault detection. The faulty phases are identified.

Sensitivity is particularly high in phase-to-phase faults when controlling with phase-to-phase voltages (VPh-Ph). This control is advantageous with compensated systems because its principle excludes pickup by single ground faults. It is adapted automatically to the existing load conditions in the case of two-phase and three-phase faults (i.e., it becomes more current sensitive during low-load operation), and the pickup threshold is higher in the case of high load currents. Table A- 3 shows the assignment of the phase currents, loop voltages and output results with single-phase pickup if control with phase-to-phase voltages is selected.

Table A-3. Voltage Controlled Overcurrent Fault Detection - With Phase-to Phase Voltages

Fault

Detection

Module

L1

L2

L3

Measured Current

L1

L2

L3

Measured	Ground Fault
Voltage	Detection
L1-L2	irrelevant
L2-L3
L3-L1

Parameter

(1705)

1PH FAULTS

irrelevant

Resultant

Loop

L1-L2

L2-L3

L3-L1

Annunciation

L1

L2

L3

If the voltage loops are set to be dependent on the ground fault detection, the high sensitivity for phase-to-ground faults then also applies to phase-to-phase faults. This possibility is, in principle, independent of the treatment of the system neutral; it assumes, however, that the ground fault criteria according to section A.2.1 have been satisfied safely for all ground faults. Table A-4 applies to the fault detection program for phase-to-ground or phase-to-phase voltages with single- phase pickup.

Table A-4. Voltage Controlled Overcurrent Fault Detection - Phase-to Ground Voltages With Ground Fault and Phase-to-PhaseVoltages Without Ground Fault

Fault

Detection

Module

L1

L2

L3

L1

L2

L3

Measured	Measured	Ground Fault
Current	Voltage	Detection
L1	L1-L2	no
L2	L2-L3	no
L3	L3-L1	no
L1	L1-E	yes
L2	L2-E	yes
L3	L3-E	yes

Parameter

(1705)

1PH FAULTS

irrelevant

irrelevant

Resultant

Loop

L1-L2

L2-L3

L3-L1

L1-E

L2-E

L3-E

Annunciation

L1

L2

L3

L1, E

L2, E

L3, E

It is also possible to control with phase-to-ground voltage loops (VPh-E) when a ground fault has been detected. Detection for phase-to-phase faults then takes place only with high-set overcurrent (I>>). This option is advantageous in systems with a low-impedance ground (resistance grounding) when only ground faults are to be detected by the voltage controlled overcurrent fault detection. The measured loop is independent of the parameter 1PH FAULTS. Table A-5 shows

A-14 July 27, 1995