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τ
Θ
The operational measured value T
values) shows the time remaining until the next restart is allowed.
Extension of
In order to properly account for the reduced heat removal when a self-ventilated motor
Cooldown Time
is stopped, the cooldown time constant can be increased relative to the time constants
for a running machine with the factor Kτ at STOP (address 6608). A stopped motor
Constant
is defined by current below an adjustable current flow monitoring threshold
BkrClosed I MIN. The assumes that the idle current of the motor is greater than
this threshold. The pickup threshold BkrClosed I MIN also effects the thermal over-
load protection function (see Section 2.9).
While the motor is running, heating of the thermal profile is modeled with the time con-
stant τ
constant τ
cooldown (slow temperature leveling) are met.
Minimum Inhibit
Regardless of thermal profiles, some motor manufacturers require a minimum inhibit
Time
time after the maximum number of permissible startup attempts has been exceeded.
The duration of the inhibit signal depends on which of the times, T
time
Depending on the setting of parameter 274 ATEX100, the value of the thermal profile
Behaviour on
Power Supply
is either reset to zero on failure of the power supply voltage, or cyclically buffered in a
Failure
non-volatile memory until the power supply voltage returns. In the latter case when
power supply is restored, the thermal profile uses the stored value for calculation and
matches it to the operating conditions.
Emergency Startup
If, for emergency reasons, motor starting in excess of the maximum allowable rotor
temperature must take place, the motor start blocking signal can be terminated via a
binary input (">Emer. Start ΘR"), thus allowing a new starting attempt. The
thermal rotor profile continues to function, however, and the maximum admissible
rotor temperature can be exceeded. No motor shutdown is initiated by the motor
restart inhibit, but the calculated overtemperature of the rotor can be observed for risk
assessment.
Blocking
If the motor restart blocking function is blocked or switched off, the thermal profile of
the rotor overtemperature and the leveling time T EQUAL as well as the minimum
inhibit time T MIN. INHIBIT are reset, and any existing motor start inhibit signal is
retracted.
Logic
The thermal profile can also be reset via a binary input. This may be useful for testing
and commissioning, and after power supply voltage restoration.
7UM61 Manual
C53000-G1176-C127-3
– rotor time constant, calculated internally:
R
τ
= t
· (n
R
Start
where:
t
= Startup time in s
Start
I
= Startup current in pu
Start
– thermal replica at the instant the motor is switched off (depends on
pre
operational condition)
calculated from the motor ratings, and the cooldown is calculated with the time
R
· Kτ at RUNNING (address 6609). In this way the requirements for a slow
R
is longer.
2.25 Restart Inhibit for Motors (ANSI 66, 49Rotor)
2
– n
) · I
cold
warm
Start
(to be found in the overload measured
ReInhib time
or T
MIN INHIBIT
ReInhib
151
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