ABB RELION REX640 Technical Manual page 651

1MRS759142 C
REX640
Technical Manual
• Mismatch due to varying tap changer positions
• Different characteristics, loads and operating conditions of the CTs
• Zero-sequence currents that flow only on one side of the power transformer
• Normal magnetizing currents
• Magnetizing inrush currents
• Overexcitation of magnetizing currents
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
G
3~
a)
GUID-012433DB-DBB2-4902-B2AA-9DC7A626DCD1 V1 EN
Figure 358: 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".
Section 4
Protection functions
TR3PTDF
3dI>T
Distance
e.g. 500 m
b)
645