Siemens siprotec 7SD5 User Manual page 52

2 Functions
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
If n'/n ≤ 1.50, setting = calculated ratio; if n'/n > 1.50, setting = 1.50
1)
With this data the device establishes an approximate CT error characteristic and cal-
culates the restraint quantity (see also Section 2.3).
Calculation example:
Current transformers 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 secondary lines is (with the resistivity for copper ρ
Ωmm
Here, the most unfavourable case is assumed, i.e. the current (as it 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
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
52
Error at Rated Current
Transforma- Angle
tion Ratio
± 60 min
1.0 %
3.0 % —
± 30 min
0.5 %
± 30 min
1.0 %
± 180 min
1.0 %
± 18 min
2
CC
= 5 A
N
2
/m)
= 0.175 Ω · (5 A)
2
= 4.375 VA
l
Error at Rated Recommended Settings
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
= 5 A is calculated
N
1)
3.0 % 10.0 %
1)
5.0 % 15.0 %
1)
1.0 % 15.0 %
1)
3.0 % 15.0 %
1)
6.0 % 20.0 %
1)
3.0 % 10.0 %
1)
5.0 % 15.0 %
= 0.0175
Cu
7SD5 Manual
C53000-G1176-C169-1