ABB RED650, Applications Manual

Page: 70 / 454

4.2.4.6 Example how to connect the open delta VT to the IED for low
impedance earthed or solidly earthed power systems
SEMOD55055-199 v6
Figure 21 gives an example about the connection of an open delta VT to the IED
for low impedance earthed or solidly earthed power systems. It shall be noted that
this type of VT connection presents secondary voltage proportional to 3U
0
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
3
Ph Ph
Ph E
U
Uo U
-
-
= =
EQUATION1926 V1 EN-US
(Equation 7)
The primary rated voltage of such VT is always equal to UPh-E 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
21 gives an overview of the actions which are needed to make this
measurement available to the built-in protection and control functions within the
IED.
Section 4
1MRK 505 393-UEN B
Analog inputs
64 Line differential protection RED650 2.2 IEC
Application manual