ABB Relion 670 series - Example How to Connect the Open Delta VT to the IED for Low Impedance Grounded or Solidly Grounded Power Systems

4.2.4.6 Example how to connect the open delta VT to the IED for low impedance
grounded or solidly grounded power systems
Figure 24 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 (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
24 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 506 369-UUS - Section 4
Analog inputs
Line distance protection REL670 2.2 ANSI 93
Application manual