Siemens SIPROTEC 7SJ62, Руководство пользователя

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Functions
2.10 Thermal Overload Protection 49
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008 193
Example: Cable and current transformer with the following data:
Permissible Continuous Current I
max
= 500 A at
Θ
u
= 40 °C
Maximum Current for 1 s I
1s
= 45 · I
max
= 22.5 kA
Current Transformer 600 A / 1 A
Example: Cable and current transformer with the following data:
Thus results:
The settings are:
49 K-FACTOR
=
0.83
;
TIME CONSTANT
=
33.7 min
Warning Elements
By setting the thermal warning element
49
Θ
ALARM
(adress
4204
), a warning message can be issued before
reaching the tripping temperature. Tripping can thus be avoided by initiating early load reduction measures.
This warning element simultaneously represents the dropout level for the trip signal. Only when this threshold
is undershot, will the tripping command be reset and the protected equipment can be switched on again.
The thermal element level is given in % of the tripping overtemperature.
A current warning level is also available (parameter
4205 I ALARM
). The setting is in secondary amperes and
should be equal to or slightly less than the permissible current k I
N sec
.. It can be used instead of the thermal
warning element by setting the thermal warning element to 100 % thus virtually disabling it
Extension of Time Constants
TIME CONSTANT
set in address
4203
is valid for a running motor. When a motor without external cooling is
running down or at standstill, the motor cools down more slowly. This behavior can be modeled by increasing
the time constant by factor
K
τ
-FACTOR
, set at address
4207
. Motor stop is detected if the current falls below
the threshold value
BkrClosed I MIN
of the current flow monitoring (see side title "Current Flow Monitoring"
in Subsection 2.1.3.2). This understands that the motor idle current is greater than this threshold. The pickup
threshold
BkrClosed I MIN
affects also the following protection functions: voltage protection and restart
inhibit for motors.
If no differentiation of the time constants is necessary (e.g. externally-cooled motors, cables, lines, etc.) the
K
τ
-
FACTOR
is set at
1
(default setting value).
Dropout Time after Emergency Starting
The dropout time to be entered at address
4208 T EMERGENCY
must ensure that after an emergency startup
and after dropout of the binary input
„>EmergencyStart“
the trip command is blocked until the thermal
replica is below the dropout threshold again.
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