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Applications
Grid Dynamics Power Quality Voltage Regulation Earth Fault Detection
Three Winding Transformer
and Reverse Power Flow
The Three Winding firmware feature is • voltage, current, cos φ, apparent-,
REGSys
available on voltage regulators REG-D active- and reactive power can be
and REG-DA. It was originally designed displayed in the transducer mode
to regulate and supervise three win- for the measurement input that
ding transformers. In the meantime it is selected for the regulation (U1,
can also be used to fulfill other appli- I1 or U2, I2) at the moment
cations like reverse power flow - and • voltage that is used for regulation
blocking scenarios, or other applications can be selected via binary input, by
in general which need a second voltage SCADA-system or by background
(U1, U2) and second current input (I1, programming. One possibility for a
I2). In these cases the firmware feature background program is the change of
is mostly combined with background the regulation voltage depending on
programming (special tool A. Eberle) to the load of the two windings. This
realize customer-specific requirements. means, the winding with the bigger
load will be regulated and the other
The main characteristics of the Three one will be supervised (standard so-
Winding firmware feature are: lution in case of three winding trans-
formers if the currents are available).
• two galvanically separated voltage – • selection of the regulated vol-
(U1, U2) and current inputs (I1, I2) tage (measurement input U1 or
(hardware feature M9) U2) is indicated on the REG-D(A)
• equal or different voltage transformer LC-Display and can be signalled
settings (VT`s) for the two measure- via SCADA and via relay
ment inputs (U1, U2), what means • all parallel programs and the cur-
three winding transformer with rent influence algorithms (ZIC or
different secondary voltage levels LDC) of the REG-D(A) can also be
can be regulated easily (CT ratio used in three winding applications
on the two measurement inputs • in case of measuring only voltages (U1,
(I1, I2) can be different either) U2) the regulation side can be defined
• display of both secondary voltages too, and can be changed depending on
in the standard transducer mode voltage limits which need to be set.
Regulation of a Three Winding Transformer
Three winding transformers are special
power transformers that have two
windings on the secondary side and
normally feed two different bus bars.
The voltage levels on the secondary
side of the power transformer can be
equal or different. In most cases these
transformers have only one OLTC
(onload tap-changer) on the primary
side, although types of two tap-changers
on the secondary side exist, so that it
is normally necessary to connect both
secondary voltages with the measure-
ment inputs (U1, U2) of the voltage
regulator REG-D(A) and to select
one of the voltages depending on the
busbar situation for the regulation.
If REG-D is equipped with PAN-D
voltage supervision unit (19”-techno-
logy), both voltages are also connected
to the PAN-D to supervise the regu-
lated voltage additionally. The change
between the measurement inputs (U1,
U2) is done in the same way as on the
REG-D. With a so called background
program – flexible tool to create
customer specific solutions either - it
is possible that the PAN-D can super-
vise both voltages at the same time.
The voltage that is used for the regu-
lation and supervision can be selected
via binary input, via SCADA-system or
by background program. It is possible
to monitor the unregulated voltage in
parallel to make sure that it stays within
a certain defined range. If current mea-
surement is available on the transformer
or at the feeder bay the REG-D(A)
can automatically select the regulation
voltage in dependence on the load.
Therefore a different background
programme is used, which is available
as a standard. In general it is possi-
ble to realize the voltage selection on
any costumer specific requirement.
The voltage which is used for regulation
is indicated on the voltage regulator
LC-Display.
As standard you will see {1} for voltage
input-1 (VT 1) and {2} for voltage input-2
(VT 2).
This indication – {1} or {2} - can be
changed to a free definable, application-
specific three character string.
In the transducer mode you can see
both secondary voltages, the frequency
and the limit for the unregulated voltage,
which is monitored. The supervision of
the unregulated voltage can be activated
and deactivated by changing the feature
3winding. The regulated voltage will be
indicated in the left upper corner with
the above marked label and an arrow in
front of the measured voltage values.
On the second transducer screen you
can find regulated voltage, current, phase
angle and active, reactive and apparent
power of the regulated measurement
inputs. To have this screen available you
need to activate the feature 3winding with
phase measurement (with measurement
input swap).
other applications
As mentioned before the three winding
feature can also be used for other appli-
cations example:
Regulation of a coupling trans-
former between two grids
In this case power flow direction can
change so that it is necessary to change
also the regulated voltage. In normal
operation the power flow is from the
HV-side to the LV-side and the LV-side is
used for measuring the regulated voltage.
That`s the typical application of voltage
regulation.
When the power flow direction changes
to reverse power flow then the HV-side
will be regulated. Therefore the VT’s and
the CT’s of the LV- and the HV-side are
connected to the voltage regulator REG-
D(A). The regulated voltage will be deter-
mined automatically by the power flow
direction that the REG-D(A) calculates
out of the measurement values.
When the HV-side is regulated the
REG-D(A) also changes the tap-com-
mand direction in order to achieve a
voltage change into the right direction.
A. Eberle GmbH & Co. KG
Frankenstraße 160
D-90461 Nürnberg
Fon +49(0)911 628108-0
Fax +49(0)911 628108-99
www.a-eberle.de
info@a-eberle.de
