Moeller ZB12 Series, Аппаратное обеспечение и инженерия

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39
05/05 AWB2300-1527D/GB
2 Configuration
Monitoring overload of
motors in the EEx e area EEx e type of protection is achieved on motors by special
constructive measures. The motors are assigned according to
the highest permissible surface temperature classes. The
temperature rise time
t
E
and the ratio between startup
current and rated current I
A
/ I
N
are calculated also and
specified on the rating plate of the motor.
The temperature rise time t
E
represents the time that expires
for the temperature of the motor winding to rise from its final
rated operational temperature up to the limit temperature,
at a startup current of
I
A
t.
However, since EEx e motors are not intrinsically safe,
explosion safety is only achieved by taking special measures
during installation and by selecting appropriate operating
conditions (PTB testing regulations), e.g. by a combination
of the circuit with a correctly rated and set overload current
protection.
Adjusting the overload
current protection
j
Warning!
The selected current overload protection system must not
only ensure proper motor current monitoring, but also that
the seized motor is switched off within the temperature
rise time
t
E
. This means, the protective device must be
rated in such a way to ensure that the tripping time
t
A
for
the ratio
I
A
/
I
N
of the EEx e motor is not higher than its
temperature rise time
t
E
according to its characteristics
curve, in order to safely switch off the motor within that
period (
a
following example).