Limiting Values; Blockings - Siemens 6MD85 Manual

Control Functions
6.9 Voltage Controller
I Load current
load
φ Rotor angle
You can also use X and R compensation for parallel control of transformers. If the X value is positive, the
voltage losses of the phase are compensated. If you are implementing parallel control with X and R compensa-
tion, then the X value is negative and considers the voltage increase from the busbar to the transformer.
If the X and R compensation are active, you must limit the maximum permitted voltage increase in relation to
the target voltage in order to avoid a voltage at the transformer that is too high. To do this, set the parameter
Vmax threshold. If the actual voltage exceeds this threshold value, no more higher adjusting commands
are issued.
6.9.3.6

Limiting Values

The limiting values cause no higher or lower adjusting commands to be given to the tap changer in the event
of an upper limit violation (Vmax threshold) or lower limit violation (Vmin threshold). In this way,
changing taps under abnormal voltage conditions and changing taps in the incorrect direction (for example, in
the event of wiring errors) is prevented.
The lower and upper tap changer limits are included in the limiting values. The parameters Lower tap-
position limit and Higher tap-position limit cause an additional restriction of the control range.
6.9.3.7

Blockings

The blockings prevent tap positions under abnormal network conditions. The following blocking functions are
available:
•
Undervoltage
•
Overcurrent, load current
•
Undercurrent
•
External blocking (binary input)
•
Blocking command LTCBlock IEC 61850
•
Blocking in the event of pickup of the transformer differential protection
Using the parameter Blocking behavior, you specify whether the blockings are to take effect only in auto-
matic operation (Auto) or in both automatic and manual operation (Auto-Manual).
Overcurrent blocking prevents tap-change operations in the event of an overload. For the current blockings,
the positive-sequence system of the load current and of the current on the upper-voltage side of transformers
is calculated.
By assigning the tap changer to the transformer side, you also arrange the current of the upper-voltage side.
Perform this assignment in the appropriate Transformer side function group. Here, you must use the tap
changer of the voltage controller.
Undervoltage blocking prevents tap-change operations in the event of a network collapse. The output signals
of the voltage controller are blocked and, depending on the operating mode, the indication
and/or Manual Blocking is issued.
464
Auto Blocking
SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017