DOC. MIE91093 Rev. 1.34 Page 104 of 145
We choose If = 8 A; the corresponding zone limit voltages are:
V1 = 1.6 V;
V2 = 3.2 V;
V3 = 8 V;
VSTART = 16 V.
We adjust all currents to 8 A; the V-I phase angle is -75° (line
side) or 105° (Busbar side); fault voltages are 1.6 V.
We start the test at 1.5 V; if trip time is 0.05 s we slightly
increase all voltages and start again, until trip time becomes
0.3 s: let us assume that VT31 is 1.55 V and VT32 is 1.65 V.
This means that first zone limit is 0.2 Ohm; the error is zero.
If instead with 1.5 V the trip time is 0.3 s we reduce all
voltages and start again, until trip time becomes 0.05 s: let us
assume that VT31 is 1.4 V and VT32 is 1.5 V. This means that
first zone limit is 0.181 Ohm; the error is -9%.
The test continues with the following fault voltages, until all
limits are tested.
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