2.14 Inverse time operation
2 Protection functions
Technical description
100
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RI and RXIDG type inverse time operation
These two inverse delay types have their origin in old ASEA
(nowadays ABB) earth fault relays.
The operation delay of types RI and RXIDG depends on the
measured value and other parameters according Equation
2.14.1-4 and Equation 2.14.1-5. Actually these equations can
only be used to draw graphs or when the measured value I is
constant during the fault. Modified versions are implemented
in the relay for real time usage.
Equation 2.14.1-4 RI
PICKUP
236
.
0
339
.
0
I
I
k
t
RI
Equation 2.14.1-5 RXIDG
PICKUP
ln
35
.
1
8
.
5
I
k
I
t
RXIDG
t
= Operation delay in seconds
k
= User‟s multiplier
I
= Measured value
I
PICKUP
= User‟s pick up setting
Example for Delay type RI :
k
= 0.50
I
= 4 pu
I
PICKUP
= 2 pu
3
.
2
2
4
236
.
0
339
.
0
5
.
0
RI
t
The operation time in this example will be 2.3 seconds. The
same result can be read from Figure 2.14.1-15.
Example for Delay type RXIDG:
k
= 0.50
I
= 4 pu
I
PICKUP
= 2 pu
9
.
3
2
5
.
0
4
ln
35
.
1
8
.
5
RXIDG
t
