Siemens siprotec SJ62, User Manual

Page: 183 / 715

2 Functions
181
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
Example: Cable and current transformer with the following data:
Permissible Continuous Current I
max
= 500 A at
Θ
u
= 104
°
F or 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 Tempera-
ture Level By setting the thermal warning level
49 Θ ALARM
at address
4204
, a warning
message can be issued prior to tripping, thus allowing time for load curtailment proce-
dures to be implemented. This warning level simultaneously represents the dropout
level for the tripping signal. Only when this threshold is undershot, the tripping
command is reset and the protected equipment may be returned to service.
The thermal warning level is given in % of the tripping temperature level.
A current warning level is also available (address
4205 I ALARM
). The setting corre-
sponds to secondary amperes, and should be set equal to, or slightly less than, per-
missible continuous current (k ·
I
Nom sec
). It may be used in lieu of the thermal warning
level by setting the thermal warning level to 100 % and thereby practically 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 margin
heading "Current Flow Monitoring" in Section 2.1.3.2). This assumes that the motor
idle current is greater than this threshold. The pickup threshold
BkrClosed I MIN
affects also the following protection functions: breaker failure 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.