ABB Relion 650 Series Applications Manual page 53

1MRK 505 287-UUS B
3)
4)
4)
4.2.4.4 Example how to connect the open delta VT to the IED for low impedance
grounded or solidly grounded power systems
Figure 16
grounded or solidly grounded power systems. It shall be noted that this type of VT connection
presents secondary voltage proportional to 3V
In case of a solid ground fault close to the VT location the primary value of 3Vo will be equal to:
V
=
Ph Ph
3 Vo
EQUATION1927-ANSI V1 EN-US
The primary rated voltage of such VT is always equal to VPh-Gnd. Therefore, three series
connected VT secondary windings will give the secondary voltage equal only to one individual VT
secondary winding rating. Thus the secondary windings of such open delta VTs quite often has a
secondary rated voltage close to rated phase-to-phase VT secondary voltage, that is, 115V or
115/√3V as in this particular example. Figure
to make this measurement available to the built-in protection and control functions within the IED.
Busbar protection REB650
Application manual
are three connections made in Signal Matrix Tool (SMT), which connect 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 then one preprocessing block might be connected in
parallel to these three VT inputs.
shows that in this example the fourth (that is, residual) input channel of the preprocessing block is
not connected in SMT tool. Thus the preprocessing block will automatically calculate 3Vo inside by
vectorial sum from the three phase to ground voltages connected to the first three input channels of
the same preprocessing block. .
is a Preprocessing block that has the 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:
VBase=66 kV (that is, rated Ph-Ph voltage)
If frequency tracking and compensation is required (this feature is typically required only for IEDs
installed in the generating stations) then the setting parameters
accordingly.
gives an example about the connection of an open delta VT to the IED for low impedance
- =
V
-
Ph Gnd
3
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DFTReference shall be set
to the IED.
0
16 gives an overview of the actions which are needed
Section 4
Analog inputs
SEMOD55055-199 v6.1.1
(Equation 4)
47