Technical description
2 Protection functions
2.24 Inverse time operation
VM259.EN007
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133
Table 2.24-1
Current input
Maximum measured
secondary current
Maximum secondary
scaled setting
enabling inverse delay
times up to full 20x
setting
I
L1
, I
L2
, I
L3
and I
0Calc
250 A
12.5 A
I
0n
= 5 A
*)
50 A
2.5 A
I
0n
= 1 A
*)
10 A
0.5 A
I
0n
= 0.2 A
*)
2 A
0.1 A
*) The availableI
0n
values depend on the order code. VAMP 259 has 5 A, 1 A
or 0.2 A residual current inputs available. Desired input needs to be
specified when ordering the relay.
Example of limitations
CT = 750/5
Application mode is Feeder
CT
0
= 100/1 (cable CT is used for residual current)
The cable CT is connected to a 1 A terminals of the available I
0
inputs.
For overcurrent stage I> the table above gives 12.5 A. Thus the
maximum setting for I> stage giving full inverse delay range is
12.5 A / 5 A = 2.5 xI
n
= 1875 A
Primary
.
For earth fault stage I
0
> the table above gives 0.5 A. Thus the
maximum setting for I
0
> stage giving full inverse delay range is
0.5 A / 1 A = 0.5 xI
0n
= 50 A
Primary
.
2.24.1.
Standard inverse delays IEC, IEEE, IEEE2, RI
The available standard inverse delays are divided in four
categories IEC, IEEE, IEEE2 and RI called delay curve
families. Each category of family contains a set of different
delay types according the following table.
Inverse time setting error signal
The inverse time setting error signal will be activated, if the
delay category is changed and the old delay type doesn't exist
in the new category. See Table 2.24-1 for more details.
Limitations
The minimum definite time delay start latest, when the
measured value is twenty times the setting. However, there are
limitations at high setting values due to the measurement
range. See Table 2.24.1-1 for more details.