Siemens 7SA511 manual Resultant Annunciation Loop

7SA511 Line Protection Relay Reference A

V 70

60

V(Iph>>)

50

V(Iph>)

40

30

20

10

Pickup

Iph>

0

0 1 2

Iph>>

3

I/IN

Figure A-4. Voltage Controlled Overcurrent Fault Detection Characteristic

Each of the three fault detection modules is controlled by the phase-to-ground voltages (VPh-E) or the phase-to-phase voltages (VPh-Ph). You must program the relay to indicate whether the phase- to-ground voltages (VPh-E) or the phase-to-phase voltages (VPh-Ph) are decisive, or whether this depends on the ground fault detection as described in section A.2.1. Optimum control largely depends on whether the system neutral is grounded with a low impedance (resistance grounded), is solidly grounded, or is not grounded (isolated or compensated).

Control with phase-to-ground voltage (VPh-E) is characterized by a high sensitivity to ground short-circuits and is, therefore, particularly advantageous in grounded systems. It is automatically adapted to the existing load conditions (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-2 shows the assignment of the phase currents, loop voltages and output results with single-phase pickup if control with phase-to-ground voltages is selected.

Table A-2.Voltage Controlled Overcurrent Fault Detection - With Phase-to-GroundVoltages

Fault Detection	Measured
Module	Current

Measured

Voltage

Ground

Fault

Detection

Parameter (1705)

1PH FAULTS

Resultant Annunciation Loop

L1

L2

L3

L1

L2

L3

L1

L2

L3

L1

L2

L3

L1

L2

L3

L1

L2

L3

L1-E

L2-E

L3-E

L1-E

L2-E

L3-E

L1-E

L2-E

L3-E

no no no

no no no

yes yes yes

PHASE-PHASE

(Uph - Uph)

PHASE-EARTH*

(Uph - E)

irrelevant

L3-L1

L1-L2

L2-L3

L1-E

L2-E

L3-E

L1-E

L2-E

L3-E

L1

L2

L3

L1

L2

L3

L1, E L2, E L3, E

* Only applicable for grounded systems

July 27, 1995 A-13