Explanations on the Connection and Current-Direction Definition
Uniform reference arrows and transformer burdens are defined for the SIPROTEC 5 device series. These agree-
ments also apply to the transformer protection devices. The special handling of the neutral-point current
described previously is a result of this.
The current definition states that the sum of the currents flowing into the protected object is equal to 0 (
I
A
+ I
B
+ I
C
+ I
N
= 0 or I
A
+ I
B
+ I
C
= -I
N
). The protected object is located to the right or left of the transformer set. The
following basic connections result from this.
[tileite2-070211-01.tif, 2, en_US]
Figure 6-273 Current-Transformer Connection (1) According to Definition
or
[tileite4-260313-01.tif, 2, en_US]
Figure 6-274 Current-Transformer Connection (2) According to Definition
The following connection is defined for the transformer according to Figure 6-275. The current flow for an
external ground fault is entered at the same time. It is recognized that the secondary currents each flow from
the device. From this, a differential current (I
Diff,REF
= |
I
Y
+ I
A
+ I
B
+ I
C
| = | -I
4
- I
3
|) results, according to the refer-
ence arrow definition for the restricted ground-fault protection (positive to the protected object) with an
Protection and Automation Functions
6.43 Restricted Ground-Fault Protection
870 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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