DANGER
Hazardous voltages during interruptions in secondary circuits of current transformers
Non-observance of the following measure will result in death, severe personal injury or substantial
property damage.
²
Short-circuit the current transformer secondary circuits before current connections to the device are
opened.
Ι
4
from own Line
To generate a delta voltage, the broken delta winding of one phase in the voltage transformer set (e.g. A) is
bypassed (refer to Figure 3-31). If no connection on the g–n windings of the voltage transformer is available,
the corresponding phase is open circuited on the secondary side. Via the current path only the current from
the current transformer in the phase from which the voltage in the voltage path is missing, is connected; the
other CTs are short-circuited. If the line carries resistive-inductive load, the protection is in principle subjected
to the same conditions that exist during a ground fault in the direction of the line.
The voltages can be read on the display at the front, or called up in the PC via the operator or service interface,
and compared with the actual measured quantities as primary or secondary values. The absolute values as
well as the phase differences of the voltages are indicated so that the correct phase sequence and polarity of
individual transformers can also be seen.
The same manipulation is carried out with the current and voltage transformers at the other end.
[polaritaetspruefung-i4-holmgreen-101010, 1, en_US]
Figure 3-31
Polarity check for Ι
4
, Example for a current transformer set in Holmgreen configuration
If the current flows towards the protected object according to the circuit in Figure 3-31, the currents Ι
B
and Ι
C
are virtually zero. A ground current 3Ι
0
of the approximately same level as Ι
A
occurs. Accordingly, the voltage
V
AGnd
is missing and a zero sequence voltage 3V
0
appears.
In the event of a polarity fault, 3Ι
0
is in opposite phase with Ι
A
or the zero voltage 3V
0
supplements the other
two voltages to a voltage star. Open the circuit breakers, short-circuit current transformers and set current and
voltage transformer connections right and repeat the test.
Mounting and Commissioning
3.3 Commissioning
SIPROTEC 4, 7SD80, Manual 243
E50417-G1100-C474-A2, Edition 02.2018
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