Siemens siprotec SJ62 User Manual page 164

Extension of Cool
Down Time Con-
stants
Behavior in Case of
Power Supply
Failure
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
2.8 Motor Protection (Motor Starting Protection 48, Motor Restart Inhibit 66)
Thus the total inhibit time T
longer than the sum of the two first mentioned times:
T = T + T
Reclose Equal Restart
T = T
Reclose Min Inhibit
The operational measured value T
the remaining time until the next restart is permissible. When the rotor excessive tem-
perature is below the restarting limit and thus the next restarting attempt is permitted,
the operational measured value for the waiting time has reached zero.
In order to properly account for the reduced heat exchange when a self-ventilated
motor is stopped, the cooling time constants can be increased relative to the time con-
stants for a running machine with the factor Kτ at STOP (address 4308). The criterion
for the motor stop is the undershooting of a set current threshold BkrClosed I MIN.
This understands that the motor idle current is greater than this threshold. The pickup
threshold BkrClosed I MIN affects also the thermal overload protection function
(see Section 2.10).
While the motor is running, the heating of the thermal profile is modeled with the time
constant τ
calculated from the motor ratings, and the cool down calculated with the
R
time constant τ x Kτ at RUNNING (address 4309). In this way, the protection caters
R
to the requirements in case of a slow cool down (slow temperature equilibrium).
For calculation of the restarting time T
with
k
τ at STOP
k
τ at RUNNING
Θ
pre
τ
R
Depending on the setting in address 235 ATEX100 of Power System Data 1 (see
Section 2.1.3.2) the value of the thermal replica is either reset to zero (ATEX100 = NO)
if the power supply voltage fails, or cyclically buffered in a non-volatile memory
(ATEX100 = YES) so that it is maintained in the event of auxiliary supply voltage failure.
In the latter case, the thermal replica uses the stored value for calculation and matches
it to the operating conditions. The first option is the default setting (see "Additional In-
formation on the Protection of Explosion-Protected Motors of Protection Type In-
creased Safety "e", C53000-B1174-C157"/5/). For further details, see /5/.
can become equal to the minimum inhibit time if it is
Reclose
for T < T
Min Inhibit Equal
≥ T
for T
Min Inhibit Equal
sive temperature > restarting limit
(visible in the thermal measured values) is
Reclose
the following applies:
Restart
– extension factor for the time constant = Kτ at STOP,
address 4308
– extension factor for the time constant = Kτ at
RUNNING, address 4309
– thermal replica at the instant the motor is switched off
(depends on operational condition)
– rotor time constant, calculated internally
+ T
Restart
+ T , if the calculated exces-
Restart
162