Siemens 7SR23 DAD Manual page 187

Nomenclature
I = Fault current corresponding to the rated stability limit (primary Amps)
F
I = Maximum prospective internal fault current (primary Amps)
Fint
I = Secondary magnetising (exciting) current of current transformer at Vs volts.
MAG
I = Non-linear resistor (Metrosil) current.
NLR
Is = Relay setting current
P.O.C. = Primary operate current (fault setting)
R = Resistance of CT secondary winding.
CT
R = Resistance of CT connection leads
L
Rstab = Resistance of stabilising resistor
T = Turns ratio of all current transformers (Primary turns / Secondary turns)
V = Maximum secondary internal fault voltage
Fint
V = Kneepoint voltage of the CT
k
Vs = Relay circuit setting voltage
©2013 Siemens Protection Devices Limited
Chapter 7) 7SR23 DAD Applications Guide
Chapter 7 Page 5 of 42