ABB eVM1 Installation And Service Instructions Manual page 82

It is also assumed that at nominal environment temperature (i.e. Environment Temperature Tenv)
and at nominal current (i.e. Nominal Motor Current IMn) the motor will reach (asymptotically) its
nominal temperature (i.e. Nominal Motor Temperature TMn), i.e.
where
∆
T
is the nominal (asymptotical) temperature increment of motor
n
T
is the environmental temperature
env
The value of ∆
T
is related to the thermal energy dissipation in the motor, and is proportional to the
n
squared value of current
In general, the value of (asymptotical) temperature increment when the generic current I is flowing
into the motor is then given by
According to the above considerations, the estimated instantaneous temperature T of the motor,
taking into account the environment temperature and the actual motor current, is calculated
according to:
To better approximate different motor operational conditions, the time constant can assume
three different values, depending on the actual motor current I, namely:
Time Constant OFF, when
Time Constant NORMAL, when
Time Constant OVERHEAT, when
The motor manufacturer can provide these values.
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