Siemens SIPROTEC 4 7UT6 Series, Руководство пользователя

Страница: 136 / 684

Time Overcurrent Protection for Phase and Residual Currents
The overcurrent protection is used as backup protection for the short-circuit protection of the main protected
object and provides backup protection for external faults which are not promptly disconnected and thus may
endanger the protected object. It can also be used as short-circuit protection for a further protected object if it
has been assigned to corresponding measuring locations (see Section
2.1.4.3 Assignment of Protection Func-
tions to Measuring Locations / Sides under “Further 3-phase Protection Functions”) and these are fed into the
correct current transformer sets.
Time overcurrent protection for phase currents takes its currents from the side or measuring location to which
it is assigned (address 420). Time overcurrent protection for residual current always uses the sum of the phase
currents of that side or measuring location to which it is assigned (address 422). The side or measuring loca-
tion for the phase currents may be different from that of the residual current.
If the main protected object is
PROT. OBJECT
=
1ph Busbar
(address 105), the time overcurrent protection
is ineffective.
The time overcurrent protection provides two definite time stages and one inverse time stage for each the
phase currents and the zero sequence current. The latter may operate according to an IEC or an ANSI, or a user
defined characteristic.
7UT6x has three overcurrent protection functions for phase and residual currents where each can be used
independent of each other at different locations. They can, e.g. be implemented independently on various
sides of the main protection object or three-phase measuring locations. Assigning the different protective
functions to the sides or one-phase measuring locations are according to Section
2.1.4.3 Assignment of
Protection Functions to Measuring Locations / Sides is performed.
The pickup and trip messages of all levels, from all O/C phase functions are included in the group indications
Overcurrent PU
and
OvercurrentTRIP
.
General
The time overcurrent protection provides two definite time stages and one inverse time stage for each of the
phase currents and the residual current. The latter may operate according to an IEC or an ANSI user require-
ments or a user defined characteristic.
Definite Time, Instantaneous Overcurrent Protection
The definite time stages (DT) for phase currents and the threefold zero sequence current (sum of the phase
currents) are also available when an inverse time characteristic was configured in the definition of the scope
of functions (address 120/130/132 and/or 122/134/136).
Pickup, Tripping
Two definite time stages are available for each the phase currents and the zero sequence current. For the
Ι
>>-
stages each phase current and the zero sequence current are compared with the common pickup values
I>>
and
3I0>>
and are signalled when exceeded. After the user-defined time delays
T I>>
or
T 3I0>>
have
elapsed, trip signals are issued that are also available for each stage. The reset value is approximately 95 %
below the pickup value for settings above
Ι
N
. For lower values the dropout ratio is reduced in order to avoid
intermittent pickup on currents near the pickup value (e.g. 90 % at 0.2 ·
Ι
N
).
Figure 2-67 and Figure 2-68 show the logic diagrams for the high-set stages
I>>
and
3I0>>
.
2.4
2.4.1
2.4.1.1
Functions
2.4 Time Overcurrent Protection for Phase and Residual Currents
136 SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016