GE MiCOM P40 Agile - Current Differential Requirements

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:
V
k
³ KI
n
(R
CT
+ 2R
L
)
where:
● V
k
= Required IEC knee point voltage
● K = Dimensioning factor
● I
n
= CT nominal secondary current
● R
CT
= CT resistance
● R
L
= One-way lead impedance from CT to relay
● K is a constant depending on the maximum value of through fault current for stability (I
f
), and the Primary
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
f
´ X/R) £ 1000 (2-end applications):
K must have the value 65 or as calculated by: K = 40 + (0.07(I
f
´ X/R)), whichever the highest.
For higher (I
f
´ X/R) up to 2600, K = 107
For IEDs with the settings: Is1 = 20%, Is2 = 2In, k1 = 30%, k2 = 100% and for (I
f
´ X/R) £ 600 (3-end applications):
K must have the value 65 or as calculated by: K = 40 + (0.35(I
f
´ X/R))
For higher (I
f
´ X/R) up to 2600, K = 256
Determination of K with transient bias enabled
For IEDs with the settings: Is1 = 20%, Is2 = 2 In, k1 = 30%, k2 = 150% (2-end applications):
K = (1.42I
f
+ 53.7)(6.06E-03 ´ X/R + 0.515)
For IEDs with the settings: Is1 = 20%, Is2 = 2 In, k1 = 30%, k2 = 100% (3-end applications):
K = (7.47 ´ I
f
+ 77.8)(8.19E-03 ´ X/R + 0.345)
This is valid for I
f
£ 50 pu and X/R £ 80
P543i/P545i Chapter 16 - Current Transformer Requirements
P54x1i-TM-EN-1 421