Permissive Intertripping; Ct Ratio Correction Setting Guidelines - GE P4A Technical Manual

P54A/B/C/E
9.8

PERMISSIVE INTERTRIPPING

The permissive intertrip (PIT) timer can be set between 0 and 200 ms. This time should be set to provide
discrimination with other protection devices. For example, if there is a genuine busbar fault, the time delay should
be set to allow busbar protection to clear the fault. A typical setting may be 100 to 150 ms.
9.9

CT RATIO CORRECTION SETTING GUIDELINES

If there is no mismatch between current transformers at line ends, Ph CT Corr'tion should be set to 1 in all devices
Note:
The following consideration includes references to currents used in Neutral Current Differential protection and protection of
feeders with In-zone transformers. If not applicable they may be ignored.
If the CTs at line ends have different primary ratings, then one of them is considered as a reference (the one with
the lowest primary rating). Ph CT Corr'tion should be set to 1 in the device connected to the reference CT. For all
other devices Ph CT Corr'tion is calculated as follows:
Ph CT Corr'tion
Settings Phase Is1, Phase Is2, Id High Set, Diff Is1, Diff Is2 must be calculated as pu of the reference primary
rating, then converted into local primary (secondary) values. For setting Phase Is1 in IEDX, the equations would be:
Phase Is1 [p.u.] = (Phase Is1
Phase Is1
IEDx PRI.
Phase Is1
IEDx SEC.
The same considerations apply to settings Phase Is2, Id High Set, In Diff Is1, Diff Is2.
Example:
Assume that we have a three-ended application with line ends X, Y, Z (500/5, 800/5, 200/1) and Current Differential
settings in absolute primary values:
Phase Is1
ABSOLUTE PRI.
Phase Is2
ABSOLUTE PRI.
Id High Set
ABSOLUTE PRI.
Diff Is1
ABSOLUTE PRI.
Diff Is2
ABSOLUTE PRI.
Setting
Phase CT Primary
Phase CT Sec'y
Ph CT Corr'tion
Phase Is1 [p.u.]
Phase Is1 (Primary)
Phase Is1 (Secondary)
Phase Is2 [p.u.]
Phase Is2 (Primary)
Phase Is2 (Secondary)
P54xMED-TM-EN-1
= (Phase CT Primary
IEDx
IABSOLUTE PRI
[A] = (Phase Is1 [p.u.]) (Phase CT Primary
[A] = (Phase Is1 [p.u.]) (Phase CT Sec'y
= 100A
= 1000A
= 3000A
= 50A
= 1000A
500A
5A
500/200 = 2.5
100/200 = 0.5
0.5*500 = 250A
0.5*5 = 2.5A
1000/200 = 5
5*500 = 2500A
5*5 = 25A
Chapter 6 - Current Differential Protection
) / (Phase CT Primary
IEDx
[A]) / (Phase CT Primary
IEDx
IEDx
End X
800A
5A
800/200 = 4
100/200 = 0.5
0.5*800 = 400A
0.5*5 = 2.5A
1000/200 = 5
5*800 = 4000A
5*5 = 25A
)
REFERENCE
[A])
REFERENCE
)
)
End Y
200A
1A
1 (reference)
100/200 = 0.5
0.5*200 = 100A
0.5*1 = 0.5A
1000/200 = 5
5*200 = 100A
5*1 = 5A
End Z
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