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[dwkonlsK-060913.vsd, 1, en_US]
Figure 8-99
Three-Winding Transformers
Three-winding transformers are special power transformers that have 2 separate windings on the secondary
circuit and typically supply 2 different busbars. The voltage levels on the secondary circuit of the power trans-
formers can either be the same or different. In addition to designs with 2 tap changers on the secondary
circuits, in most cases, three-winding transformers are equipped with only one tap changer or on-load tap
changer on the primary side. It is therefore necessary to feed both voltages of the secondary windings to the
voltage measuring inputs (V1, V2) and to specify one of them, depending on the busbar situation, to the
voltage controller as the control variable.
The voltages of side 1 and 2 of the three-winding transformer are simultaneously monitored. In the process,
the voltage to be controlled can be automatically selected via the load current of both sides or by using one
parameter. This parameter is the settings group switching via binary input, protocol, or function keys. The
uncontrolled voltage can be monitored in parallel to ensure that it remains within the defined voltage limits.
If a current measuring point is assigned to a function group, the voltage to be controlled can be automatically
selected dependent on the load.
For automatic on-load tap changing, the voltage of the transformer side into which the larger load current
flows is controlled. The respective uncontrolled voltage is monitored for undervoltage and overvoltage.
In contrast to overvoltage on the controlled side, for overvoltage on the uncontrolled side, the higher impulse
is blocked and no fast step down to a lower tap occurs. In case of undervoltage on the uncontrolled side, the
lower adjusting commands are blocked if this behavior is activated for undervoltage supervision.
SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
Voltage-Controller Constellation for Two-Winding Transformers without Current Measurement
Control Functions
8.9 Voltage Controller
1197
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