Siemens SIPROTEC Manual page 51

Table 2-1 Recommended settings for current transformer data
CT class Standard
5P IEC 60044-1
10P
TPX IEC 60044-1
TPY
TPZ
PX IEC 60044-1
BS: Class X
C100 ANSI
to
C800
1)
If n'/n ≤ 1.50, setting = calculated ratio; if n'/n > 1.50, setting = 1.50
With this data the device establishes an approximate CT error characteristic and calculates the restraint quan-
tity (see also Section 2.3).
Calculation example:
Current transformer 5P10; 20 VA
Transformation 600 A / 5 A
Internal burden 2 VA
Secondary lines 4 mm
Length 20 m
Device 7SD5 , I
Burden at 5 A, 0.3 VA
The resistance of the secondary lines is (with the resistivity for copper ρ
Here, the most unfavourable case is assumed, i.e. the current (as is the case with single-phase faults) flows
back and forth via the secondary lines (factor 2). From that the power for nominal current I
P = 0.175 Ω · (5 A)
l
The entire connected burden consists of the burden of the incoming lines and the burden of the device:
P' = 4.375 VA + 0.3 VA = 4.675 VA
Thus the ratio of the accuracy limit factors is as follows
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
Error at rated current
Transforma- Angle
tion ratio
1,0 % ± 60 min
3,0 % —
0,5 % ± 30 min
1,0 % ± 30 min
1,0 % ± 180 min
± 18 min
2
Cu
= 5 A
N
2
= 4.375 VA
Error at rated
accuracy limit
Address 251 Address 253 Address 254
factor
≤ 5 % ≤ 1,50
≤ 10 % ≤ 1,50
ε ≤ 10 % ≤ 1,50
ε ≤ 10 % ≤ 1,50
ε ≤ 10 % ≤ 1,50
(only I∼)
≤ 1,50
≤ 1,50
Recommended settings
1)
3,0 %
1)
5,0 %
1)
1,0 %
1)
3,0 %
1)
6,0 %
1)
3,0 %
1)
5,0 %
2
= 0.0175 Ωmm /m)
Cu
= 5 A is calculated
N
Functions
2.1 General
10,0 %
15,0 %
15,0 %
15,0 %
20,0 %
10,0 %
15,0 %
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