Siemens siprotec SJ62 User Manual page 163

2 Functions
Restarting Limit
Restart Time
Equilibrium Time
Minimum Inhibit
Time
Total Time T
Reclose
161
If the rotor temperature has exceeded the restart threshold, the motor cannot be re-
started. The blocking signal is not lifted unless the rotor temperature has fallen below
the restarting limit, that is, when exactly one start becomes possible without exceeding
the excessive rotor temperature limit. Based on the specified motor parameters the
device calculates the normalized restarting limit Θ
Where:
Θ
=
Restart
k =
R
=
I
Start
=
I
B
T =
m
τ
=
R
n =
cold
The restarting limit Θ
Restart
measured values".
The motor manufacturer allows a maximum allowable cold (n
starting attempts. Afterwards the device must be allowed to cool off! A certain time
must elapse - restarting time t
This thermal behavior is provided for in the protection as follows: Each time the motor
is shutdown, the timer starts (address 4304 T Equal). It takes into account the differ-
ent thermal conditions of the motor parts at the moment of shutdown. During the equi-
librium time, the thermal profile of the rotor is not updated. It is maintained constant to
replicate the equilization process in the rotor. Then the thermal model with the corre-
sponding time constant (rotor time constant x extension factor) cools down. During the
equilibrium time the motor cannot be restarted. As soon as the temperature sinks
below the restarting threshold, the next restart attempt can be made.
Regardless of thermal profiles, some motor manufacturers require a minimum inhibit
time after the maximum number of permissible starting attempts has been exceeded.
The total duration of the inhibit signal depends on which of the times T
or T is longer.
Restart
The total waiting time T
posed of the equilibrium time and the time T
and the value that is needed to drop below the limit for restarting. If the calculated tem-
perature rise of the rotor is above the restarting limit when the motor is shut down, the
minimum inhibit time will be started together with the equilibrium time.
Temperature threshold below which restarting is possible
k-factor for the rotor, calculated internally
Startup current
Basic current
Maximum starting time
Thermal time constant of the rotor, calculated internally
Permitted starts with cold motor
is displayed as operational measured value in the "thermal
- to ensure that the rotor has cooled off.
Restart
, before the motor can be restarted, therefore is com-
Reclose
Restart
:
Restart
) and warm (n
cold
Min Inhibit
calculated from the thermal profile,
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
)
warm