DOC. MIE91093 Rev. 1.34
Page 96 of 145
Z1 = (VT11+VT12)/(2*If*(1+KoL))
Once a limit has been found, repeat the test for other zone
limits. During these tests, current and phase are no more
modified.
Example. Let us assume that the distance relay to be tested
has the following settings at line angle (75°).
ZONE LIMIT
ONE
TWO
THREE
STARTER
IMPEDANCE Ohm 0.2
0.4
1
2
TIMING
s
0.05
0.3
0.6
1.2
Let us assume: KoL = 1; IV0 = 2.5 A; VN = 57.8 V (100 V).
Maximum test current is:
IMAX = 57.8/(2*(1+1)) = 14.4 A.
We choose If = 8 A; the corresponding zone limit voltages are:
V1 = 3.2 V;
V2 = 6.4 V;
V3 = 16 V;
VSTART = 32 V.
We adjust the current of I1 to 8 A; the V-I phase angle is -75°
(line side) or 105° (Busbar side); V1 fault voltage is 3.2 V; V2
and V3 are 57.8 V.
We start the test at 3 V; if trip time is 0.05 s we slightly
increase V1 and start again, until trip time becomes 0.3 s: let
us assume that VT11 is 3.5 V and VT12 is 3.6 V. This means
that first zone limit is 0.221 Ohm; the error is + 10%.
If instead with 3 V the trip time is 0.3 s we reduce V1 and
start again, until trip time becomes 0.05 s: let us assume that
VT11 is 2.9 V and VT12 is 3 V. This means that first zone limit
is 0.185 Ohm; the error is -7.4%.
The test continues with the following fault voltages, until all
limits are tested. The starter limit is found between 1.2 s trip
