Sef Protection (Core-Balanced Ct); Directional Elements; Non-Directional Elements; Low Impedance Ref Protection - GE MiCOM P40 Agile Technical Manual

Chapter 9 - Current Transformer Requirements
2.4

SEF PROTECTION (CORE-BALANCED CT)

2.4.1

DIRECTIONAL ELEMENTS

Instantaneous element
I
≥ +
fn
(
V R
K CT
2
Note:
Ensure that the phase error of the applied core balance current transformer is less than 90 minutes at 10% of rated current
and less than 150 minutes at 1% of rated current.
2.4.2

NON-DIRECTIONAL ELEMENTS

Time delayed element
I
≥ +
cn
V ( R
K CT
2
Instantaneous element
≥ +
(
V I R
K sn CT
Note:
Ensure that the phase error of the applied core balance current transformer is less than 90 minutes at 10% of rated current
and less than 150 minutes at 1% of rated current.
2.5

LOW IMPEDANCE REF PROTECTION

For X/R < 40 and 
< 15
f
≥ +
V 24 I R (
K n CT
For 40 < X/R < 120 and 15
≥ +
V 48 I R (
K n CT
Note:
Class x or Class 5P CTs should be used for low impedance REF applications.
2.6

HIGH IMPEDANCE REF PROTECTION

The high impedance REF element will maintain stability for through-faults and operate in less than 40ms for
internal faults, provided the following equations are met:
( 2
I R
+
f CT
R
=
st
I
s
202
+
2 )
R Rn
L
+
2 R Rn )
L
+
2 )
R Rn
L
n
2 R )
L
< If < 40
n n
2 R )
L
)
R
L
P14x
P14xEd1-TM-EN-1