2.21 Use in auto-transformer systems
205
7ST6 Manual
E50417-G1176-C251-A3
2.21
Use in auto-transformer systems
This function is optional, i.e. not included in all device variants.
The system 2x15 kV (or 2x25 kV) is used increasingly in a.c. power traction networks
to enhance the transmission properties. Additional auto-transformers and a return line
- negative feeder - of 15 kV (or 25 kV) potential are characteristic of this type of infeed.
For this reason, two-pole switching devices are necessary in the overhead contact line
system.
2.21.1 Functional Description
General
Since auto-transformer systems require current inputs for summation, they can only
be implemented in devices that feature 3 analog inputs each. It can be specified in pa-
rameter
CURRENT I1, I2
whether the protective function operates only with the
overhead line current or with the summation current of overhead line and negative
feeder. In the latter case, the two currents are detected via separate transformers, vec-
torially added and in the further process treated as a measured quantity. Please con-
sider also the polarity of the current transformer (current of the negative feeder) at
IF
CT STARPOINT
for determination of direction. The measured value connections can
be found in the Appendix at A.3. These settings apply to all functions, not including
some exceptions.
The following functions are treated differently:
• No use of the summation currents for the functions
Overload protection, It measurement and defrost protection.
• In case of the high-speed overcurrent protection, the selection is additionally made
via jumper X600 on the module C-I/O 13.
• The current-dependent statistic values are always calculated from the overhead
line current.
All three currents (overhead line current, negative feeder current and the resulting
summation current) are generally available for detection and display of the operational
measured values and fault recording.
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