19
The ratio of differential current transformer is defined as:
100
100
1
0
1
2
1
'
'
'
I
I
I
I
I
（
B.1
）
Current Transformer relay request a current
1
I
equal to the maximum short-circuit
current, the ratio difference is less than or equal to 10%. Difference in the ratio equivalent
to 10%, the secondary current
2
I
, and conversion to a secondary lateral excitation
current
'
1
I
between the current
0
I
and meet the following relationship:
0
1
10
I
I
'
（
B.2
）
0
2
9
I
I
（
B.3
）
Definite M as a multiple of the maximum short-circuit current, K for the current transformer
ratio, there are
N
N
N
M
I
I
I
K
I
K
I
I
M
2
0
2
'
1
1
1
10
（
B.4
）
Where
M
I
1
The largest one-side short-circuit current
N
I
1
Rated current for one side
N
I
2
Rated current for the secondary side
When Ration error is 10 percent, the maximum allowable burden impedance
B
Z
is
calculated as:
2
0
0
2
2
0
9
Z
I
E
Z
I
E
Z
B
（
B.5
）
Where
2
Z
For the current transformer secondary winding impedance
0
E
Is Current transformer secondary winding for the induction electromotive force, and
the relationship between
0
E
and
0
I
is the characteristic curves described by the
excitation.
