ISA T1000 PLUS - Three Phase Fault

DOC. MIE91093 Rev. 1.34 Page 101 of 145
The approximation is that we change only fault voltages and
not the corresponding angle: the drawing explains the
approximation.
If the fault voltage needs to be increased more than 5%; else,
also phase angles must be computed and changed.
In our example, at first test the relay trips in zone N, with Vf =
20 V; on next test (higher voltage) the relay trips in zone
N+1, with Vf = 20.5 V; then:
Z = (20 + 20.5) / (4 * 10) = 1.012 Ohm.
1.12.7 Three phase fault
In single phase faults, voltage and current vectors are
modified during the test as shown in the following figure.
V
R N
V
R
V
T V
S
V
T N
V
S N

I
R
I
S
I
T
V2
V3
Vf1
V’3
Vf2
V’2