GE MiCOM P145 Agile - SEF Protection (Core-Balanced CT); Directional Elements; Non-Directional Elements; Low Impedance REF Protection

2.4 SEF PROTECTION (CORE-BALANCED CT)
2.4.1 DIRECTIONAL ELEMENTS
Instantaneous element
V
I
R R Rn
K
fn
CT L
≥ + +
2
2( )
Note:
Ensure that the phase err
or 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
V
I
R R Rn
K
cn
CT L
≥ + +
2
2( )
Instantaneous element
V I R R Rn
K sn CT L
≥ + +( )2
Note:
Ensure that the phase err
or 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 
f
< 15
n
V I R R
K n CT L
≥ +24 2( )
For 40 < X/R < 120 and 15
n
< If < 40
n
V I R R
K n CT L
≥ +48 2( )
Note:
Class x or Class 5P CT
s 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 ar
e met:
R
I R R
I
st
f CT L
s
=
+( )2
Chapter 9 - Current Transformer Requirements P14x
202 P14xEd1-TM-EN-1