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7UT51 v3
2
Description of Relay
2.1
Overview
The Siemens 7UT51 multifunction protective relay
provides three-phase protection for two (7UT512) or
three (7UT513) winding transformers, shunt reactors,
motors, generators, short lines, or buses. The 7UT513
model has two ground current inputs that can be used
to increase the sensitivity of the differential protection.
The relay matches currents mathematically, so
complicated CT wiring schemes are not necessary.
The 7UT51 features selectable variable percentage
differential and selectable harmonic restraints. An
active algorithm recognizes CT saturation and
unequal CT performance and restrains pickup. These
abilities provide typical trip times of one cycle or less
with high security.
In addition to the differential protection (87T/87HS,
87M/G, or 87B), the 7UT51 relay provides
current-model based thermal overload protection
(49-1 and 49-2) for two selected windings. High-set
(50HS) and definite/inverse time overcurrent
protection (50/51) are available for one selected
winding. The 7UT513 model can provide either ground
differential protection (87N) of one winding or tank
leakage protection (64T). See Figure 2.1 and
Table 2.1 for the possible combinations of protection
functions.
The model 7UT513 relay's third set of three-phase
inputs can apply the additional protection functions to
an
additional zone, which may be independent or overlap
the main zone containing the main protected device.
This additional-zone protection provides added
flexibility and security in a range of applications.
PRIM-2330C
2.2
Features
2.2.1
Protection Overview
•
Microprocessor-based full numerical
implementation with self-diagnostics of internal
operation and CT circuits.
•
Mathematically matched currents enable use of
simple wye-connections of CTs.
•
Three-phase, variable-slope percentage
differential protection (87T, 87M/87G, or 87B).
•
Unrestrained high-set differential protection
(87HS) when protecting a transformer.
•
Restraint of differential protection when a
through-fault causes CT saturation.
•
Zero sequence current elimination (7UT512 or
7UT513) or correction (7UT513 only).
•
2nd harmonic restraint (inrush) and
higher-harmonic restraint (3rd, 4th or 5th) when
protecting a transformer.
•
Thermal overload protection (49-1 and 49-2,
current-based thermal model) for any two
windings.
•
High-set (50HS) and definite/inverse (50/51) time
overcurrent protection for any one winding.
•
Ground differential protection (87N) of any one
winding, or tank leakage protection (64T) (7UT513
only).
•
Any protection function (except for differential
protection) can be used to protect a separate,
additional device or zone (7UT513 only).
Description of Relay
2
13
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