Siemens 7SA511 manual Is replaced by Which gives us

7SA511 Line Protection Relay	Method of Operation
IL1	ZL
	L1
VL1
IL2	ZL

L2

VL2

L3

E

Figure A-5. Phase-to-Phase Short Circuit Loop

For calculation of a phase-to-ground loop for a short circuit in L3-E (Figure A-6), observe that the impedance of the ground return path is not normally equal to the impedance of the phase. In the loop equation

IL3 ZL − IE ZE = VL3− E ,

ZE is replaced by

ZE

ZL , which gives us

ZL

I

Z

− I

Z

ZE

= V

,

L ZL

L3

L

E

L 3− E

from which you obtain the line impedance

ZL

=

VL3− E

,

IL3

−

ZE

IE

ZL

whereby the factor ZE is dependent only upon the line constants and not on the distance to the

ZL

fault.

A-16 July 27, 1995