Siemens 7SA511 manual I L

7SA511 Line Protection Relay Reference A

the assignment of the phase currents, loop voltages and output results for single-phase pickup with ground fault detection only.

Table A-5. Single-Phase, Voltage Controlled Overcurrent Fault Detection - Phase-to-GroundVoltage With Ground Fault Detection Only

Fault Detection	Measured
Module	Current
L1	L1
L2	L2
L3	L3
L1	L1
L2	L2
L3	L3

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

Parameter (1705)

1PH FAULTS

irrelevant

irrelevant

Resultant	Annunciation
Loop
L1-E	L1, E
L2-E	L2, E
L3-E	L3, E

no pickup and annunciation by VPH-E</I>

A.3 Determination of the Faulted Loops

A.3.1 Verification of the Faulted Loop(s)

The currents and voltages of the faulty loop are used for calculation of the fault impedance. The phase selective fault detector determines the faulted loop and determines the corresponding measurement values for impedance calculation. The selection of valid short circuit loops varies considerably, depending upon whether the system is grounded, isolated, or compensated.

For example, when calculating the impedance of a phase-to-phase loop for a two phase short circuit in L1-L2 (Figure A-5), the following identity applies:

	IL1 ZL − IL2 ZL = VL1 − VL1
where	V and I are complex measured values (phasors),
and	Z = R + jX is the complex line impedance.

The line impedance is

Z		=	VL1	− VL 2	.
	L
			IL1	− IL 2

July 27, 1995 A-15