Engineering; Overload Monitoring Of Ex E Motors; Setting Of The Overcurrent Protection Device - Eaton PKE12 Series Manual

10/15 MN03402004Z-DE/EN
Overload monitoring
of Ex e motors
Setting of the overcurrent
protection device
j
6

Engineering

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. In addition, temperature rise time t
ratio of the starting current to the rated operational current
I /I are also determined and specified on the motor.
A N
The temperature rise time t
ature of a winding rises from the final temperature in normal
operation to the limit temperature when a starting current is
present I .
A
However, e motors are not safe on their own. 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.
Danger!
The current-dependent protective device must be selected
so that not only the motor current is monitored but also
the blocked motor is switched off within the temperature
rise time t . This means that the protective device must be
E
rated in such a way as to ensure that tripping time t
the explosion-proof electric motor's ratio I
longer than the motor's temperature rise time t
to the motor's characteristic curve. This is to ensure that
the motor will be reliably switched off within the temper-
ature rise time.
The tolerance of the overcurrent release of g20 % is to be
observed (a following example).
is the time in which the temper-
E
/I
A N
E
and the
E
for
A
is not
according
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