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7.4 Current Transformer Selection
7 Applications
Technical description
164
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VM265.EN011
Example 1
Transformer:
16 MVA YNd11 Z
k
= 10%
110 kV / 21 kV (84 A / 440 A)
CT’s on HW side:
100/5 5P10
Winding resistance R
CT
= 0.07
(RCT depends on the CT type, INCT and power rating. Let's say that the
selected CT type, 100 A and an initial guess of 15 VA yields to 0.07
.)
Safety factor c = 4.
(Transformer differential, earthed Y.)
CTs on LV side:
500/5 5P10
(Max. Short circuit curent is 4400 A = 8.8 x 500 A)
Winding resistance R
CT
= 0.28
(RCT depends on the CT type, INCT and power rating. Let's say that the
selected CT type, 500 A and an initial guess of 15 VA yields to 0.28
)
Safety factor c = 3.
(Transformer differential,
.)
Differential current setting of the non-stabilized stage
I>>:
I
SET
= 9 x I
N
R
L
= 0.008
Typical burden of a VAMP relay current input.
R
WHV
= 0.138
Wiring impedance of high voltage side.
(2x16 m, 4 mm
2
)
R
WLV
= 0.086
Wiring impedance of low voltage side.
(2x10 m, 4 mm
2
)
The needed CT power on HV side will be
6
.
14
5
07
.
0
008
.
0
138
.
0
07
.
0
100
10
84
9
4
2
N
S
VA
15 VA is a good choice for HV side.
And on the LV side
2
.
15
5
28
.
0
008
.
0
086
.
0
28
.
0
500
10
440
9
3
2
N
S
VA
15 VA is a good choice for LV side.
Содержание 265
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