Siemens 6MD85 Manual page 575

Both additional functions DLC and RDT are mutually exclusive, because the DLC checks if the value falls below
a voltage threshold, while the RDT checks if the value exceeds the voltage threshold.
The respectively selected additional function runs in the automatic reclosing state dead time.
Reduced Dead Time (RDT)
With the Reduced dead time, a close command can be assigned before the expiration of the set dead times if
the line to switch on is recognized as fault-free through the measurement of the line voltage.
The voltage measurement occurs with the 3 phase-to-phase-voltages.
In systems with a grounded neutral point, the 3 phase-to-ground voltages are additionally observed.
In systems with compensated or with isolated neutral points, the largest 2 of the 3 phase-to-ground voltages
are additionally considered. Through this, a RDT can also be executed with 1-phase ground connections.
For the approval of the close command with RDT, the following conditions apply:
•
The automatic reclosing function is in the state dead time.
•
Each measured voltage is above the set threshold values Volt. thres.f. live line/bus
The phase-to-phase voltages are divided by √3 prior to comparing the threshold value. Thus, the phase-
to-ground voltage U
•
Exceeding the threshold is fulfilled for the set duration Voltage supervision time.
Dead-Line Check (DLC)
If after switching off a short-circuit the voltage on the switched off line does not disappear, the automatic
reclosing function can be avoided with the dead-line check (DLC).
The voltage measurement occurs with the 3 phase-to-ground voltages.
For the release of the close command with DLC, the following conditions apply:
•
The automatic reclosing function is in the state dead time.
•
All measured voltages for the set duration Voltage supervision time are below the set threshold
Volt. thres.f. live line/bus.
•
The set dead time is expired.
As soon as the voltages fall below the threshold value for the set duration, the allowance for automatic
reclosing with DLC is assigned. This also applies if the values are not below the voltage threshold until the
expiration of the set dead time. In this way, an automatic reclosing is executed if the automatic reclosing func-
tion is first switched to at the end of the protected line and thus, the line is exposed to voltage again.
The automatic reclosing function is blocked by the DLC under the following conditions:
•
The automatic reclosing function is in the Closure state, the dead time has expired
•
All measured voltages were not simultaneously below the set threshold values Volt.thres. f. dead
line/bus for the set duration Voltage supervision time during the dead time.
SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017
√3 applies as the reference size for the parameterization.
N
Protection and Automation Functions
7.2 Automatic Reclosing Function
575