ISA T1000 PLUS User Manual page 99

DOC. MIE91093 Rev. 1.34 Page 99 of 145
2) Phase to phase fault voltage
The phase to phase voltage is:
Vf = Z*If*2
For instance: If = 10 A
Vf = 20 * Z; with Z = 1 Ohm, Vf = 20 V.
3) Phase fault voltage
For both faulty phases, the phase fault voltage is:
VX = 0.5* sqrt(VN^2 + Vf^2)
For instance, if Z = 1 Ohm; If = 10 A; Vf = 20 V; VN = 57.8
V,
VX = 30.58 V
The third phase does not change its amplitude, equal to VN.
4) Phase angle
We will compute first of all the angle of fault voltage with
respect to the voltage when the fault amplitude is zero, φX1,
that is:
φX1 = atg(Vf/VN)
φX1
V2 V3
V'3
Vf
Given this angle, the following table summarizes the pre-fault
angle and the fault angle for all types of test.
FAULT 1-2 2-3 3-1