401
6
F
2
S
0
8
5
0
<Accuracy limit factor of CTs is given>
Table K-2 CT Requirement defined by n’
Td [ms]
Requirement 1
Requirement 2
35
n’ I
n
≧
3.75
×
I
fmax
n’
I
n
≧
7.5
×
I
f_z1_max
50
n’ I
n
≧
3.75
×
I
fmax
n’
I
n
≧
8.75
×
I
f_z1_max
75
n’ I
n
≧
5
×
I
fmax
n’
I
n
≧
10
×
I
f_z1_max
100
n’ I
n
≧
5
×
I
fmax
n’
I
n
≧
10
×
I
f_z1_max
150
n’ I
n
≧
10
×
I
fmax
n’
I
n
≧
10
×
I
f_z1_max
Td [ms]
Requirement 3
Requirement 4
35
n’ I
n
≧
2.5
×
I
f_rev_max
n’
I
n
≧
I
Lmax
×
18
50
n’ I
n
≧
3.75
×
I
f_rev_max
n’
I
n
≧
I
Lmax
×
25
75
n’ I
n
≧
7.5
×
I
f_rev_max
n’
I
n
≧
I
Lmax
×
36
100
n’ I
n
≧
7.5
×
I
f_rev_max
n’
I
n
≧
I
Lmax
×
46
150
n’ I
n
≧
7.5
×
I
f_rev_max
n’
I
n
≧
I
Lmax
×
63
n
R
R
R
I
R
n
ct
ct
n
VA
⋅
+
+
=
2
2
/
'
(K-1)
n’
: Equivalent accuracy limit factor defined by the
equation above.
I
n
: Secondary rated current
R
VA
: Rated secondary burden [VA]
R
ct
: Secondary CT resistance [ohms]
R
2
: Actual secondary burden [ohms]
n
: Rated accuracy limit factor
I
fmax
: Maximum secondary fault current
I
f_z1_max
: Maximum secondary fault current at the zone 1 reach point
I
f_rev_max
: Maximum secondary fault current for a close-up reverse fault
I
Lmax
: Maximum secondary load current
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.
CASE 2. The case with the distance protection applied as a back-up protection with time delay
When the distance protection is applied as back-up protection the CT requirement for GRL100
can be ignored. If instantaneous tripping of distance protection is allowed when a communication
failure occurs to the current differential protection, it is recommended that the requirement for
case 1 should be applied.
<Step 1> Check the maximum through fault current I
fmaxth
I
fmaxth
< 65 X I
n
where,
I
fmaxth
: Secondary maximum through fault current
I
n
:Rated secondary current
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Summary of Contents for GRL100-701B
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