Siemens SIPROTEC 7UT613 series Manual page 38

2 Functions
Differential Protec-
tion
38
Figure 2-1 Transformer bank, consisting of 3 single-phase auto-transformers with current
comparison via each single phase
• Such current comparison is more sensitive to 1-phase earth faults in one of the
transformers than the normal differential protection. This has a certain importance
considering that 1-phase earth faults are the most probable faults in such banks.
• On the other hand, the compensation winding cannot and must not be included into
this protection even if it is accessible and equipped with current transformers. This
application variant is based on the current law in that all currents flowing into a
winding must total to zero.
• If this protection variant is desired, set address 105 to PROT. OBJECT = Autotr.
node.
• Equal setting is valid for generators and motors. The setting PROT. OBJECT =
Generator/Motor also applies to series reactors and shunt reactors, if a com-
plete 3-phase set of current transformers is connected to both sides.
• For the operation of mini-busbars set PROT. OBJECT = 3ph Busbar. The
maximum number of feeders is determined by the number of three-phase measure-
ment inputs of the device. 7UT613 and 7UT633 allow a maximum number of 3,
7UT635 a maximum of 5 measuring locations. This setting applies also to short
lines which are terminated by two sets of current transformers. „Short " means that
the current transformer connections from the CTs to the device cause no impermis-
sible burden for the current transformers.
• If the device is used as busbar as 1-phase device or via summation transformer as
3-phase device, the setting PROT. OBJECT = 1ph Busbar applies. The maximum
number of feeders is determined by the number of single-phase measurement
inputs of the device (7UT613 and 7UT633 provide up to 9, 7UT635 up to 12 mea-
surement inputs).
The differential protection is the main protective function of the device. Address 112
DIFF. PROT. is thus set to Enabled.
7UT613/63x Manual
C53000-G1176-C160-2