Figure 276: Differential protection of a generator-transformer block and short
cable/line
TR2PTDF can also be used in three-winding transformer applications or two-
winding transformer applications with two output feeders.
On the double-feeder side of the power transformer, the current of the two CTs
per phase must be summed by connecting the two CTs of each phase in parallel.
Generally this requires the interposing CTs to handle the vector group and/or ratio
mismatch between the two windings/feeders.
The accuracy limit factor for the interposing CT must fulfill the same requirements
as the main CTs. Please note that the interposing CT imposes an additional burden
to the main CTs.
The most important rule in these applications is that at least 75 percent of the
short-circuit power has to be fed on the side of the power transformer with only
one connection to the protection relay.
Protection functions
1MRS757644 H
534
620 series
Technical Manual
