3)
are three connections made in the Signal Matrix tool (SMT), Application configuration tool
(ACT), which connects these three voltage inputs to first three input channels of the
preprocessing function block 5). Depending on the type of functions, which need this
voltage information, more than one preprocessing block might be connected in parallel to
these three VT inputs
4)
shows that in this example the fourth (that is, residual) input channel of the preprocessing
block is not connected in SMT. Note. If the parameters U
L1
, U
L2
, U
L3
, U
N
should be used
the open delta must be connected here.
5)
Preprocessing block has a task to digitally filter the connected analog inputs and calculate:
•
fundamental frequency phasors for all four input channels
•
harmonic content for all four input channels
•
positive, negative and zero sequence quantities by using the fundamental frequency
phasors for the first three input channels (channel one taken as reference for
sequence quantities)
These calculated values are then available for all built-in protection and control functions
within the IED, which are connected to this preprocessing function block in the
configuration tool. For this application most of the preprocessing settings can be left to the
default values. However the following settings shall be set as shown here:
ConnectionType=Ph-Ph
UBase=13.8 kV
If frequency tracking and compensation is required (this feature is typically required only
for IEDs installed in the generating stations) then the setting parameters
DFTReference
shall be set accordingly.
4.2.4.5
Example on how to connect an open delta VT to the IED for high
impedance earthed or unearthed networks
SEMOD55055-163 v9
Figure
gives an example about the wiring of an open delta VT to the IED for
high impedance earthed or unearthed power systems. It shall be noted that this type
of VT connection presents a secondary voltage proportional to 3U0 to the IED.
In case of a solid earth fault close to the VT location the primary value of 3Uo will
be equal to:
3 0
3
3
Ph Ph
Ph N
U
U
U
-
-
=
×
= ×
EQUATION1921 V3 EN-US
(Equation 3)
The primary rated voltage of an open Delta VT is always equal to U
Ph-E
. Three
series connected VT secondary windings gives a secondary voltage equal to three
times the individual VT secondary winding rating. Thus the secondary windings of
open delta VTs quite often have a secondary rated voltage equal to one third of the
rated phase-to-phase VT secondary voltage (110/3V in this particular example).
Figure
gives overview of required actions by the user in order to make this
measurement available to the built-in protection and control functions within the
IED as well.
1MRK 511 407-UEN C
Section 4
Analog inputs
Phasor measurement unit RES670 2.2 IEC
71
Application manual
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