Toshiba GRL100-701B Instruction Manual page 403

<Step 2> Check the CT satisfies the condition given by table K-3 or K-4 depending on CT types.
Each table has 2 requirements. Both must be satisfied.
<Knee point voltage of CTs is given>
Td [ms]
35
50
75
100
150
V : Knee point voltage [V]
k
R : Secondary CT resistance [ohms]
ct
R
: Actual secondary burden [ohms]
2
I : Maximum secondary fault current
fmax
I : Maximum secondary load current
Lmax
<Accuracy limit factor of CTs is given>
Td [ms]
35
50
75
100
150
R
=
VA
n '
R
n' : Equivalent accuracy limit factor defined by the equation above.
I : Secondary rated current
n
R : Rated secondary burden [VA]
VA
R : Secondary CT resistance [ohms]
ct
R : Actual secondary burden [ohms]
2
n : Rated accuracy limit factor
I : Maximum secondary fault current
fmax
I : Maximum secondary load current
Lmax
Note : The values in the table are based on the following assumption.
- 100% DC component is superimposed.
- Only one CT is saturated.
- No remnance flux is assumed.
Table K-3 CT Requirement defined by V
Requirement 1
V ≧ I (R + R )×3
k fmax ct 2
V ≧ I (R + R )×3
k fmax ct 2
V ≧ I (R + R )×4
k fmax ct 2
V ≧ I (R + R )×4
k fmax ct 2
V ≧ I (R + R )×8
k fmax ct 2
Table K-4 CT Requirement defined by n'
Requirement 1
n' I ≧ 3.75 × I
n fmax
n' I ≧ 3.75 × I
n fmax
n' I 5 × I
≧
n fmax
n' I 5 × I
≧
n fmax
n' I ≧ 10 × I
n fmax
+
2
/ I R
⋅
n ct
n
+
R
2 ct
 402 
6 F 2 S 0 8 5 0
k
Requirement 2
V ≧ I (Rct+ R )×14.4
k Lmax 2
V ≧ I (Rct+ R )×20
k Lmax 2
V ≧ I (Rct+ R )×28.8
k Lmax 2
V ≧ I (Rct+ R )×36.8
k Lmax 2
V ≧ I (Rct+ R )×50.4
k Lmax 2
Requirement 2
n' I ≧ I
×18
n Lmax
n' I ≧ I
×25
n Lmax
n' I ≧ I
×36
n Lmax
n' I ≧ I
×46
n Lmax
n' I ≧ I
×63
n Lmax
(K-1)