Siemens 7SC80 Manual page 493

!
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
²
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
corresponding phase is disconnected on the secondary side (see
former which is not provided with voltage in its voltage path is fed into the current path. If the line carries
resistive- inductive load, the protection is subject to the same conditions as exist during a ground fault in line
direction.
Directional ground fault protection must be configured as enabled and activated (address 116). Its pickup
threshold must be below the load current of the line; if necessary, the pickup threshold must be reduced. The
parameters that have been changed must be noted.
After switching the line on and off again, the direction indication must be checked: In the fault log the
messages 67N picked up and Ground forward must at least be present. If the directional pickup is not
present, either the ground current connection or the displacement voltage connection is incorrect. If the
wrong direction is indicated, either the direction of load flow is from the line toward the busbar or the ground
current path has a swapped polarity. In the latter case, the connection must be rectified after the line has been
isolated and the current transformers short-circuited.
If the pickup message is missing, the measured ground (residual) current or the displacement voltage
emerged may be too small. This can be checked via operational measured values.
Important! If parameters were changed for this test, they must be returned to their original state after
completion of the test !
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
3-33). If no connection on the e–n windings of the voltage transformer is provided, the
Mounting and Commissioning
Figure 3-34). Only the current of the trans-
3.3 Commissioning
493