Siemens 7SJ85 - Page 1592

IEC 60044-6 (transient response),
class TPS
Classes TPX, TPY, TPZ
K≈ 1
K
SSC
≈ K
ALF
You can find a calculation example in the above section Accuracy
Limiting Factors with: K
SSC
≈ K
ALF
T
P
depending on power system and specified closing sequence
with
V
k
Knee-point voltage
R
Ct
Internal burden
R
BN
Rated burden
I
rated,sec
Secondary rated transformer current
K
ALF
Rated accuracy limiting factor
V
s.t.max
Secondary terminal voltage at 20 I
rated,prim
V
al
Secondary magnetization limit voltage
K Dimensioning factor
K
SSC
Factor symmetric rated fault current
T
P
Primary time constant
Cable Core Balance Current Transformer
The requirements to the cable core balance current transformer are determined by the function Sensitive
ground-fault detection.
The recommendations are given according to the standards IEC 60044-1 and IEC 61869-2.
Table A-5
Requirements to the cable core balance current transformer according to IEC 60044-1 and
IEC 61869-2
Transformation ratio, typical
It may be necessary to select a different transforma-
tion ratio to suit the specific power system and thus
the corresponding amount of the maximum ground
fault current.
60 / 1
Accuracy limiting factor FS = 10
Power 1 to 4 times the connected burden (device input plus
infeeds)
Notes concerning the power:
The burden of the sensitive ground-current input is very low (0.05 VA or 0.1 VA). Thus, an underburden of
more than factor 4 is probable. In this case, clarify the suitability of the class accuracy concerning an impor-
tant underburden with the transformer manufacturer. If necessary, request the accuracy for the range from 0
VA to the rated burden. This specification is then outside the standard, but in practice, it is possible in most
cases.
(Relevant standard: IEC 61869-2, Chapter 5.6.201.4 Extended burden range. There, the range 1 VA to rated
burden is specified for rated burdens smaller than 15 VA.)
Table A-6 Minimum Required Class Accuracy Depending on Neutral Grounding and Function Operating
Principle
Neutral Point Isolated Resonant-Grounded High-Resistance
Grounded
Function directional Class 1 Class 1 Class 1
Appendix
A.6 Current Transformer Requirements
1592 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017