|
Phase-failure sensitivity Overload relays Z offer, due to their design, an
effective protection against phase failure. They have phase failure sensitivity to
IEC 947-4-1 and therefore can also provide protection for EEx e motors (following diagramms).
When the
bimetallic strips in the main current section of the relay deflect as a result of three-phase motor overloading,
all three act on a trip bar and a differential bar. A shared trip lever switches over the
auxiliary contact when the limits are reached. The trip and differential bars lie against
the bimetallic strips with uniform pressure. If, in the event of phase failure for instance, one bimetallic strip
does not deflect (or recover) as strongly as the other two, then the trip and differential bars
will cover different distances. This differential movement is converted in the device by a
step-up mechanism into a supplementary tripping movement, and thus accelerates the tripping action.
Design note
section Motor protection in special applications;
Further
information to motor protection
→ section
All about Motors.
|
Trip
bridge 
