TR3PTDF is designed mainly for protection of two-winding or three-winding
transformers. TR3PTDF can also be used for the protection of generator-
transformer blocks as well as short cables and overhead lines. If the distance
between the measuring points is relatively long in line protection, interposing CTs
might be needed to reduce the burden of the CTs. For the interposing CT, the
accuracy limit factor must fulfill the same requirements as for the main CTs. The
interposing CT imposes an additional burden to the main CTs.
TR3PTDF
3dI>T
Distance
e.g. 500 m
b)
TR3PTDF
3dI>T
G
3~
a)
Figure 417: Differential protection of a generator-transformer block and short cable
or line
TR3PTDF can be used in three-winding transformer applications or two-winding
transformer applications with two output feeders.
On the double-feeder side of the two-winding power transformer, the currents
from the other feeder are connected to the third three-phase current set of the
protection relay (
Current group 3 type
to be set as "Wnd 2 restraint").
If the double-feeder side is on the input side of the transformer,
Current group 3
type
must be set as "Wnd 1 restraint".
In three-winding transformer applications, currents from winding 3 are always
connected to the third three-phase current input set of the protection relay (
Current
group 3 type
to be set as "Winding 3").
In the normal two-winding transformer application with one set of three-phase
currents on both sides of the transformer, the
Current group 3 type
setting must be
set as "Not in use".
1MRS759142 F
Protection functions
REX640
Technical Manual
733
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