31
01/11 MN03402002Z-DE/EN
2
Engineering
Overload monitoring of
Ex e motors
The Ex e protection of motors is achieved by means of
special design measures. The motors are assigned to temper-
ature classes on the basis of the highest permissible surface
temperatures. The temperature rise time t
E
and the ratio
between startup current and rated operational current I
A
/I
N
are calculated in addition 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
.
However, Ex e motors are not intrinsically safe. Explosion
safety can only be achieved by taking additional measures
during installation and by selecting appropriate operating
conditions (PTB testing regulations), e.g. by adding a
correctly rated and set overload protection to the circuit.
Setup of the overcurrent
protection system
j
Danger!
The selected overload protection system must not only
ensure proper monitoring of the motor current, but also
that the seized motor is switched off within the tempera-
ture rise time t
E
.
This means:
The protective device must be rated in such a way so as to
ensure that the tripping time t
A
for the ratio I
A
/I
N
of the
Ex 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).
Содержание PKZM4/XTPR DC1 Series
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