Current Differential Requirements - GE MiCOM P40 Agile Technical Manual

P543i/P545i
3

CURRENT DIFFERENTIAL REQUIREMENTS

We strongly recommend class X or class 5P Current Transformers. The CT knee point voltage should comply with
the minimum requirements of the formulae shown below:
³ KI
V (R + 2R
k n CT
where:
V = Required IEC knee point voltage
●
k
K = Dimensioning factor
●
I = CT nominal secondary current
●
n
R = CT resistance
●
CT
R = One-way lead impedance from CT to relay
●
L
K is a constant depending on the maximum value of through fault current for stability (I
●
system X/R ratio
Determination of K with transient bias disabled
For IEDs with the settings: Is1 = 20%, Is2 = 2In, k1 = 30%, k2 = 150% and for (I
K must have the value 65 or as calculated by: K = 40 + (0.07(I
´ X/R) up to 2600, K = 107
For higher (I
f
For IEDs with the settings: Is1 = 20%, Is2 = 2In, k1 = 30%, k2 = 100% and for (I
K must have the value 65 or as calculated by: K = 40 + (0.35(I
´ X/R) up to 2600, K = 256
For higher (I
f
Determination of K with transient bias enabled
For IEDs with the settings: Is1 = 20%, Is2 = 2 In, k1 = 30%, k2 = 150% (2-end applications):
+ 53.7)(6.06E-03 ´ X/R + 0.515)
K = (1.42I
f
For IEDs with the settings: Is1 = 20%, Is2 = 2 In, k1 = 30%, k2 = 100% (3-end applications):
K = (7.47 ´ I + 77.8)(8.19E-03 ´ X/R + 0.345)
f
£ 50 pu and X/R £ 80
This is valid for I
f
P54x1i-TM-EN-1
)
L
Chapter 16 - Current Transformer Requirements
´ X/R) £ 1000 (2-end applications):
f
´ X/R)), whichever the highest.
f
´ X/R) £ 600 (3-end applications):
f
´ X/R))
f
), and the Primary
f
421