Functions
2.37 Restart Inhibit for Motors (ANSI 66, 49Rotor)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
257
Prolonging the Cooling Time Constant
In order to properly account for the reduced heat removal when a self-ventilated motor 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 motor at standstill is defined by current below an adjustable current threshold BkrClosed
I MIN. This assumes that the idle current of the motor is greater than this threshold. The pickup threshold
BkrClosed I MIN also affects the thermal overload protection function (see Section 2.11).
While the motor is running, heating of the thermal profile is modeled with the time constant τ
R
calculated from
the motor ratings, and the cooldown is calculated with the time constant τ
R
· Kτ at RUNNING (address 6609).
In this way the requirements for a slow cooldown (slow temperature leveling) are met.
Minimum Inhibit Time
Regardless of thermal profiles, some motor manufacturers require a minimum inhibit 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
MIN INHIBIT
or T
Rem.
, is longer.
Behaviour on Power Supply Failure
Depending on the setting of parameter 274 ATEX100, the value of the thermal profile is either reset to zero on
failure of the power supply voltage, or cyclically buffered in a 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 calcula-
tion and matches it to the operating conditions.
Emergency Startup
If, for emergency reasons, motor starting that will exceed the maximum allowable rotor temperature must take
place, the motor start blocking signal can be terminated via a binary input („>Emer. Start ΘR“), thus allow-
ing a new starting attempt. The thermal rotor profile continues to function, however, and the maximum admis-
sible rotor temperature can be exceeded. No motor shutdown will be initiated by motor start blocking, but the
calculated excessive temperature of the rotor can be observed for risk assessment.
Blocking
If the motor start blocking function is blocked or switched off, the thermal profile of the excessive rotor temper-
ature and the equilibrium time T EQUAL as well as the minimum inhibit time T MIN. INHIBIT are reset, and
any existing motor start inhibit signal is terminated.
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