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(or object to be protected). This is not necessarily identical with the direction of the normal the power flow. For
all three phases, the directional messages to the power flow must be reported properly.
If all directions differ from each other, individual phases in current or voltage transformer connections are inter-
changed, not connected properly or phase assignment is incorrect. After isolation of the line and short-circuiting
of the current transformers the connections must be checked and corrected. The measurements must then be
repeated.
Finally, switch off the protected power line.
Note
Reset the pickup values changed for the check to valid values.
3.3.10
Polarity Check for Current Input I
General
If the standard connection of the device is used with current input I
current transformers (see also connection circuit diagram in Appendix A.3), then the correct polarity of the
ground current path usually occurs automatically.
If, however, current I
Appendix A.3), an additional direction check with this current is necessary.
If the device features the sensitive current input for I
system, the polarity check for I
section. Then this section is not relevant.
Otherwise the test is done with a disconnected trip circuit and primary load current. It must be noted that during
all simulations that do not exactly correspond with situations that may occur in practice, the non-symmetry of
measured values may cause the measured value monitoring to pick up. This must therefore be ignored during
such tests.
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.
Short-circuit the current transformer secondary circuits before current connections to the device are opened.
Directional Testing for Grounded Systems
The test can be performed with the „Directional ground fault protection" function (address 116).
In the following the check is described using the „directional ground fault protection" function (address 116) as
an example.
To generate a displacement voltage, the e–n winding of one phase in the voltage transformer set (e.g. A) is
bypassed (see Figure 3-19). If no connection on the e–n windings of the voltage transformer is provided, the
corresponding phase is disconnected on the secondary side (see Figure 3-20). Only the current of the trans-
former which is not provided with voltage in its voltage path is fed into the current path. If the line carries resis-
tive-inductive load, the protection is subject to the same conditions as exist during a ground fault in line direc-
tion.
SIPROTEC, 7SC80, Manual
E50417-G1140-C486-A1, Release date 12.2011
N
is derived from a separate summation CT (see e.g. a connection circuit diagram in the
N
was already carried out with the ground fault check according to the previous
N
connected in the neutral point of the set of
N
and if it is used in an isolated or resonant-grounded
N
Mounting and Commissioning
3.3 Commissioning
227
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