ABB RELION RET670, Applications Manual

Page: 101 / 1016

4.2.4.6 Example how to connect the open delta VT to the IED for low
impedance grounded or solidly grounded power systems
SEMOD55055-199 v6
Figure 25 gives an example about the connection of an open delta VT to the IED for
low impedance grounded or solidly grounded power systems. It shall be noted that this
type of VT connection presents secondary voltage proportional to 3V
0
to the IED.
In case of a solid ground fault close to the VT location the primary value of 3Vo will be
equal to:
3
3
Ph Ph
Ph Gnd
V
Vo V
-
-
= =
EQUATION1927-ANSI V1 EN-US
(Equation 7)
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
25 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.
1MRK 504 163-UUS A
Section 4
Analog inputs
Transformer protection RET670 2.2 ANSI 95
Application manual